ieee std 1534 eee standards ieee standards substations

WITHDRAWN IEEE Std 1534™-2002

IEE

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IEEE Recommended Practice forSpecifying Thyristor-ControlledSeries Capacitors

Published by The Institute of Electrical and Electronics Engineers, Inc.3 Park Avenue, New York, NY 10016-5997, USA

20 November 2002

IEEE Power Engineering Society

Sponsored by theSubstations Committee

IEE

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Print: SH95002PDF: SS95002

Authorized licensed use limited to: UNIVERSIDADE DE SAO PAULO. Downloaded on November 21,2013 at 01:04:22 UTC from IEEE Xplore. Restrictions apply.

WITHDRAWN Recognized as an IEEE Std 1534TM-2002American National Standard (ANSI)


Sponsor

Substations Committeeof theIEEE Power Engineering Society

Approved 13 June 2002

IEEE-SA Standards Board

Abstract: Recommended practices for specifying Thyristor-Controlled Series Capacitor (TCSC)installations used in series with transmission lines are provided. Ratings for TCSC thyristor valveassemblies, capacitors, and reactors as well as TCSC control characteristics, protective features,cooling systems, testing, commissioning, training, documentation, operation, and maintenance areaddressed.Keywords: power oscillation damping, series capacitors, subsynchronous resonance, TCSC,thyristor valves

The Institute of Electrical and Electronics Engineers, Inc.3 Park Avenue, New York, NY 10016-5997, USA

Copyright � 2002 by the Institute of Electrical and Electronics Engineers, Inc.All rights reserved. Published 20 November 2002. Printed in the United States of America

Print: ISBN 0-7381-3299-3 SH95002PDF: ISBN 0-7381-3300-0 SS95002

No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the priorwritten permission of the publisher.


WITHDRAWN IEEE Standards documents are developed within the IEEE Societies and the Standards Coordinating Committees of theIEEE Standards Associations (IEEE-SA) Standards Board. The IEEE develops its standards through a consensusdevelopment process, approved by the American National Standards Institute, which brings together volunteersrepresenting varied viewpoints and interests to achieve the final product. Volunteers are not necessarily members of theInstitute and serve without compensation. While the IEEE administers the process and establishes rules to promotefairness in the consensus development process, the IEEE does not independently evaluate, test, or verify the accuracy ofany of the information contained in its standards.

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Note: Attention is called to the possibility that implementation of this standard may require use of subjectmatter covered by patent rights. By publication of this standard, no position is taken with respect to theexistence or validity of any patent rights in connection therewith. The IEEE shall not be responsible foridentifying patents for which a license may be required by an IEEE standard or for conducting inquires intothe legal validity or scope of those patents that are brought to its attention.

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WITHDRAWN

Copyright � 2002 IEEE. All rights reserved. iii

Introduction

(This introduction is not a part of IEEE Std 1534-2002, IEEE Recommended Practice for Specifying

Thyristor-Controlled Series Capacitors.)

This introduction provides some background on the rationale used to develop this recommendedpractice. This information is meant to aid in the understanding and usage of this recommendedpractice.

This recommended practice describes rating considerations for Thyristor-Controlled Series Capacitor(TCSC) installations used in series with a transmission line. It is intended for

a) Individuals or organizations that use TCSC installations and acquire these stations fromsuppliers.

b) Individuals or organizations that influence how TCSC installations are acquired from suppliers.c) Suppliers interested in providing TCSC installations to purchasers.

This recommended practice is designed to help organizations and individuals to

d) Incorporate equipment ratings during the definition, evaluation, selection, and acceptance ofTCSC installations for operational use.

e) Determine how TCSC installations should be evaluated, tested, and accepted for delivery to endusers.

This recommended practice is intended to satisfy the following objectives:

f) Promote consistency between organizations when acquiring TCSC installations from suppliers.g) Identify issues that differentiate TCSC installations from conventional series capacitor

installations and provide useful practices for rating TCSCs during acquisition planning.h) Provide useful practices on evaluating supplier capabilities to meet purchaser requirements.

Participants

At the time this recommended practice was completed, the Thyristor-Controlled Series CapacitorWorking Group had the following membership:

Duane R. Torgerson, Chair

Stan Miske, Vice Chair

Wayne Litzenberger, Secretary

Bharat Bhargava Victor Gor Ben MehrabanHubert Bilodeau Richard Haas Nicholas MillerTodd Campbell Edward Horgan Jan SamuelssonAty Edris John Joyce Hector SarmientoCarlos Gama Lutz Kirschner Bo Wikstrom

Gerald Lee


WITHDRAWN The following members of the balloting group voted on this recommended practice. Balloters mayhave voted for approval, disapproval, or abstention.

Hanna Abdallah Farshad Hormozi Jeffrey NelsonArun Arora Gerhard Juette Carlos PeixotoMichael Baker George G. Karady Paul PillitteriHubert Bilodeau Stephen R. Lambert James RuggieriTodd Campbell Thomas LaRose Jan SamuelssonTommy Cooper Gerald Lee Michael SharpRichard Crowdis George Lester Harinderpal SinghGuru Dutt Dhingra Peter Lips Rao ThallamGary Engmann Wayne Litzenberger Duane R. TorgersonCarlos Gama Albert Livshitz Heinz TyllPhilip Hopkinson Gregory Luri John VithayathilEdward Horgan Gary Michel James Wilson

Nicholas Miller

When the IEEE-SA Standards Board approved this recommended practice on 13 June 2002, it had thefollowing membership:

James T. Carlo, Chair

James H. Gurney, Vice Chair

Judith Gorman, Secretary

Sid Bennett Arnold M. Greenspan Peter H. LipsH. Stephen Berger James H. Gurney Nader MehravariClyde R. Camp Raymond Hapeman Daleep C. MohlaRichard DeBlasio Donald M. Heirman William J. MoylanHarold E. Epstein Richard H. Hulett Malcolm V. ThadenJulian Forster* Lowell G. Johnson Geoffrey O. ThompsonHoward M. Frazier Joseph L. Koepfinger* Howard L. WolfmanToshio Fukuda Don Wright

*Member Emeritus

Also included are the following nonvoting IEEE-SA Standards Board liaison:

Alan H. Cookson, NIST RepresentativeSatish K. Aggarwal, NRC Representative

Savoula Amanatidis,IEEE Standards Managing Editor

iv Copyright � 2002 IEEE. All rights reserved.


WITHDRAWN Contents

1. Overview......................................................................................................................................... 1

1.1 Scope .................................................................................................................................... 1

1.2 Purpose ................................................................................................................................ 1

2. References ...................................................................................................................................... 1

3. Definitions, special symbols, acronyms, and abbreviations ........................................................... 2

3.1 Definitions............................................................................................................................ 2

3.2 Special symbols .................................................................................................................... 4

3.3 Acronyms and abbreviations ............................................................................................... 5

4. Service conditions........................................................................................................................... 6

5. Operating and rating considerations.............................................................................................. 6

5.1 Introduction ......................................................................................................................... 6

5.2 TCSC characteristics ............................................................................................................ 9

5.3 Basis for TCSC ratings ...................................................................................................... 10

5.4 Duty cycle .......................................................................................................................... 13

5.5 Operational objectives........................................................................................................ 16

6. Thyristor valves (bidirectional) .................................................................................................... 18

6.1 Current and voltage capability .......................................................................................... 18

6.2 Valve control...................................................................................................................... 23

6.3 Valve cooling system.......................................................................................................... 26

6.4 Mechanical design.............................................................................................................. 26

6.5 Valve testing....................................................................................................................... 27

7. Capacitors and reactors ............................................................................................................... 30

7.1 General............................................................................................................................... 30

7.2 Capacitor considerations.................................................................................................... 30

7.3 Reactor considerations....................................................................................................... 30

Copyright � 2002 IEEE. All rights reserved. v


WITHDRAWN 8. Control and protection .............................................................................................................. 31

8.1 Control............................................................................................................................ 31

8.2 Protection........................................................................................................................ 34

8.3 Monitoring and recording .............................................................................................. 35

8.4 Signal transmission and platform power ........................................................................ 38

8.5 General requirements...................................................................................................... 39

8.6 Coordination with line protection .................................................................................. 40

9. Layout ........................................................................................................................................ 40

9.1 General ........................................................................................................................... 40

9.2 Substation yard............................................................................................................... 41

9.3 Platform assemblies ........................................................................................................ 41

9.4 Control building ............................................................................................................. 41

10. Safety.......................................................................................................................................... 42

10.1 Personnel protection ....................................................................................................... 42

10.2 Discharge devices ............................................................................................................ 42

10.3 Grounding provisions ..................................................................................................... 42

10.4 Handling and disposal .................................................................................................... 42

11. Testing and commissioning ........................................................................................................ 42

11.1 Introduction .................................................................................................................... 42

11.2 Design and production tests and factory control system tests ....................................... 43

11.3 On-site tests..................................................................................................................... 44

12. Losses and loss evaluation ......................................................................................................... 46

12.1 Introduction .................................................................................................................... 46

12.2 Ambient conditions......................................................................................................... 46

12.3 Calculation of losses ....................................................................................................... 47

13. Reliability, availability, and maintainability .............................................................................. 48

13.1 Introduction .................................................................................................................... 48

13.2 Definitions....................................................................................................................... 48

13.3 RAM analysis ................................................................................................................. 49

vi Copyright � 2002 IEEE. All rights reserved.


WITHDRAWN 13.4 Spare parts ...................................................................................................................... 49

13.5 Availability and reliability .............................................................................................. 50

14. Project scope .............................................................................................................................. 50

14.1 Introduction .................................................................................................................... 50

14.2 New TCSC installations ................................................................................................. 50

14.3 Retrofit to an existing fixed series capacitor installation................................................ 52

15. Training ...................................................................................................................................... 53

15.1 General............................................................................................................................ 53

15.2 Off-site training............................................................................................................... 53

15.3 On-site training ............................................................................................................... 54

15.4 Training during commissioning ...................................................................................... 54

16. Documentation........................................................................................................................... 54

16.1 Introduction .................................................................................................................... 54

16.2 Purchaser documentation ............................................................................................... 54

16.3 Supplier documentation.................................................................................................. 55

Annex A (informative) Bibliography and annotated bibliography.................................................... 57

Annex B (informative) TCSC application studies and computer models.......................................... 65

Annex C (normative) Summary outline of TCSC specification......................................................... 74

Copyright � 2002 IEEE. All rights reserved. vii


WITHDRAWN


WITHDRAWN


1. Overview

1.1 Scope

This is a recommended practice for specifying Thyristor-Controlled Series Capacitor (TCSC)installations used in series with transmission lines and should be used together with IEEE Std824-1994 when specifying TCSC installations. The document addresses issues that consider ratings forTCSC thyristor valve assemblies, capacitors, and reactors as well as TCSC control characteristics,protective features, cooling systems, testing, commissioning, training, documentation, operation, andmaintenance. This document does not provide recommended practices for the development of TCSCcomputer models. However, this document does present issues that need to be considered when deve-loping TCSC computer models as discussed in Annex B (informative). Annex C (normative) provides asummary outline of recommended items that should be consideredwhen preparing aTCSC specification.

1.2 Purpose

This recommended practice is meant to provide assistance and guidance to planning, substation,apparatus, commissioning, and operation engineers in the course of specifying TCSC installations.Users of this document should tailor these recommendations to their specific project requirements.

2. References

This recommended practice shall be used in conjunction with the following publications. When thefollowing publications are superseded by an approved revision, the revision shall apply:

IEC 60068-1-1998, Environmental Testing, Part 1: General and Guidance.1

Copyright � 2002 IEEE. All rights reserved. 1

1IEC publications are available from the Sales Department of the International Electrochemical Commission, Case postale

131, 3, rue de Varembe, CH-1211, Geneve 20, Switizerland/Suisse (http://www.icc.ch/). IEC publications are also available in the

United States from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York,

NY 10036, USA.


WITHDRAWN IEC 60068-2-2-1974, Basic Environmental Testing Procedures, Part 2: Tests—Tests B: Dry Heat.

IEC 60068-2-3-1969, Basic Environmental Testing Procedures, Part 2: Tests—Tests C: Damp Heat,Steady State.

IEC 61000-4-2-2001, Electromagnetic Compatibility (EMC)—Part 4-2: Testing and MeasurementTechniques—Electrostatic Discharge Immunity Test.

IEEE Std 693TM-1997, IEEE Recommended Practice for Seismic Design of Substations.2,3

IEEE Std 824TM-1994, IEEE Standard for Series Capacitors in Power Systems.

IEEE Std 1031TM-2000, IEEE Guide for the Functional Specification of Transmission Static VarCompensators.

IEEE Std 1267TM-1999, IEEE Guide for Development of Specification for Turnkey SubstationProjects.

IEEE Std C37.90.1TM-2002, IEEE Standard for Surge Withstand Capability (SWC) Tests for Relaysand Relay Systems Associated with Electric Power Apparatus.

IEEE Std C57.16TM-1996, IEEE Standard Requirements, Terminology, and Test Code for Dry-TypeAir-Core Series-Connected Reactors.

3. Definitions, special symbols, acronyms, and abbreviations

3.1 Definitions

Some of the definitions used in this recommended practice can be found in IEEE 100TM, TheAuthoritative Dictionary of IEEE Standards Terms, Seventh Edition [B13]. In some instances, thedefinition in IEEE 100 may be either too broad or too restrictive. In such a case, an additionaldefinition or note has been included. Definitions used in this standard should be used together withthose found in IEEE Std 824-1994 when specifying TCSC installations.

3.1.1 bidirectional thyristor valve: An arrangement of thyristor valves capable of conducting currentin two directions.

NOTE—See Figure 1.

3.1.2 bypass current: The current flowing through the bypass switch, protective device, thyristorvalve, or other devices, in parallel with the series capacitor.

3.1.3 capacitive range: TCSC operation resulting in an effective increase of the power frequencyreactance range of the series capacitor.

3.1.4 conduction interval (s): That part of a cycle during which a thyristor valve is in the conductingstate.


2 Copyright � 2002 IEEE. All rights reserved.

2The IEEE standards or products referred to in Clause 2 are trademarks owned by the Institute of Electrical and Electronics

Engineers, Inc.3IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331,

Piscataway, NJ 08855-1331, USA (http://standards.ieee.org/).

IEEEStd 1534-2002 IEEE RECOMMENDED PRACTICE FOR SPECIFYING


WITHDRAWN 3.1.5 control angle (a): The time expressed in electrical angular measure from the capacitor voltage(VC) zero crossing to the starting of current conduction through the thyristor valve.


3.1.6 dynamic overload: The power frequency line current (ID) and voltage (VD) at which the TCSCshould be capable of continuous control for a short duration (typically 10 s) at rated frequency andambient temperature range.

3.1.7 platform control power: Energy source(s) available at platform potential for performingthyristor valve firing, protection, and control functions.

3.1.8 platform-to-ground cooling/air-handling insulator: An insulator that encloses cooling/airhandling paths between platform and ground level.

3.1.9 reactive power rating: The reactive power rating (PQ¼ 3IR2XR) for the TCSC bank as

determined from rated reactance (XR) and rated current (IR).

3.1.10 temporary overload: The power frequency line current (IT) and voltage (VT) at which theTCSC should be capable of continuous control for a short duration (typically 30 min) at the ratedfrequency and ambient temperature range.

3.1.11 thyristor-controlled series capacitor (TCSC) bank: An assembly of thyristor valves, thyristorreactor(s), capacitors, and associated auxiliaries, such as structures, support insulators, switches, andprotective devices, with control equipment required for a complete operating installation.

3.1.12 thyristor electronics (TE): Electronic circuits at thyristor valve potential(s) that performcontrol functions.

3.1.13 thyristor reactor: One or more reactors connected in series with the thyristor valve.


3.1.14 thyristor valve enclosure: A platform-mounted enclosure containing thyristor valve(s) withassociated valve cooling and electronic hardware.

3.1.15 thyristor varistor: An assembly of varistor units that limit overvoltages to a given value. Inthe context of TCSCs, the thyristor varistor is typically defined by its ability to limit the voltageacross a thyristor valve to a specified protective level while absorbing energy. The thyristor varistoris designed to withstand the temporary overvoltages and continuous operating voltage across thethyristor valve.

3.1.16 valve blocking: An operation to prevent further firing of a thyristor valve by inhibitingtriggering.

3.1.17 valve deblocking: An operation to permit firing of a thyristor valve by removing valve-blocking action.

3.1.18 valve base electronics (VBE): An electronic unit that provides an interface between thecontrol equipment, at earth potential, and the thyristor electronics (TE).

3.1.19 voltage-breakover operation (VBO): An operation that is designed to turn on a thyristorvalve based on a protective voltage level that appears across the thyristors. The protective level is


IEEETHYRISTOR-CONTROLLED SERIES CAPACITORS Std 1534-2002


WITHDRAWN normally set at a specified voltage level and coordinated with the capacitor bank varistor protectivelevel. Voltage breakover operation can be used for the primary protection of the capacitor and canoperate during external as well as internal faults.

3.2 Special symbols

3.2.1 IC: Current through the series capacitor.


3.2.2 ID: The power frequency line current at which the TCSC should be capable of continuouscontrol for a short duration (typically 10 s) at the rated power frequency and ambient temperaturerange.

3.2.3 IF: The line current that the TCSC might experience during a major power system disturbancefor which protective control actions are allowed (bypass breaker closed).

3.2.4 IL: Power frequency line current.


3.2.5 IMIN: The minimum line current (IL) at which the TCSC should be capable of continuouscontrol at rated frequency and rated ambient temperature range.

3.2.6 IR: The RMS line current (IL) at which the TCSC should be capable of continuous control ofthe rated reactance (XR) at rated voltage (VR), power frequency, and ambient temperature range.

3.2.7 IT: The power frequency line current at which the TCSC should be capable of continuouscontrol for a sustained period (typically 30 min) at the rated frequency and ambient temperaturerange.

3.2.8 ITH: Current through the bidirectional thyristor valve.


3.2.9 VC: Voltage across the TCSC.


3.2.10 VD: The power frequency voltage across each phase of the TCSC at which the TCSC shouldbe capable of continuous control for a short duration (typically 10 s) at the rated reactance (XD),current (ID), frequency, and ambient temperature range.

3.2.11 VMIN: The minimum TCSC RMS voltage (VC) at which the TCSC should be capable ofcontinuous control at rated power frequency and rated ambient temperature range.

3.2.12 VPL: The voltage protective level of the varistors or other protective device.

3.2.13 VR: The power frequency voltage across each phase of the TCSC that can be continuouslycontrolled at rated reactance (XR), current (IR), frequency, and ambient temperature range.

3.2.14 VT: The power frequency voltage across each phase of the TCSC at which the TCSC shouldbe capable of continuous control for a short duration (typically 30 min) at the rated reactance(XT), current (IT), frequency, and ambient temperature range.




WITHDRAWN 3.2.15 X(a): TCSC power frequency reactance as a function of thyristor control angle (a).

3.2.16 XB: The inductive reactance for each phase of the TCSC at a¼ 0� with rated continuouscurrent (IR) and frequency.

3.2.17 XC: The power frequency reactance for each phase of the TCSC bank with thyristor firingblocked with a capacitor (C) internal dielectric temperature of 25 �C.

3.2.18 XD: The power frequency reactance for each phase of the TCSC at which the TCSC shouldbe capable of continuous control for a short duration (typically 10 s) at the rated current (ID),voltage (VD), frequency, and ambient temperature range.

3.2.19 XM: The maximum power frequency reactance for each phase of the TCSC at a¼ aM, whichcan be continuously controlled at rated frequency and ambient temperature range.

3.2.20 XORDER: The ratio of X(a) divided by XC.

3.2.21 XR: The power frequency reactance for each phase of the TCSC which can be continuouslycontrolled at rated continuous current (IR), continuous voltage (VR), frequency, and ambienttemperature range.

3.2.22 XT: The power frequency reactance for each phase of the TCSC at which the TCSC shouldbe capable of continuous control for a short duration (typically 30 min) at the rated current (IT),voltage (VT), frequency, and ambient temperature range.

3.3 Acronyms and abbreviations

ATP alternative transient programBIL basic impulse levelCCVT coupling capacitor voltage transformerEMTP electromagnetic transient programETT electrically triggered thyristorsFSC fixed series compensationGPS global positioning systemHVDC high-voltage direct currentLTT light-triggered thyristorsMC master controlMTBF mean time between failureMTTR mean time to repairMvar megavarPOD power oscillation dampingRAM reliability, availability, and maintainabilityRIV radio influence voltageRMS root mean squareRTO regional transmission organizationRTU remote terminal unitSCADA supervisory control and data acquisitionSER sequence events recorderSSR subsynchronous resonance




WITHDRAWN SVC static var compensatorTCR thyristor-controlled reactorTCSC thyristor-controlled series capacitorTE thyristor electronicsTNA transient network analyzerVBE valve base electronicsVBO voltage-breakover operation

4. Service conditions

The purchaser should specify the service conditions for operation of the TCSC installation (referenceIEEE Std 824-1994) at the specified current, voltage, frequency, and fault sequence ratings, including:

a) Altitudeb) Ambient temperaturec) Ice loadd) Wind velocitiese) Seismic conditionsf) Snow depthg) Exposure to dusth) Exposure to salt, damaging fumes, or vaporsi) Swarming insectsj) Flocking birdsk) Conditions requiring over insulation or extra leakage distance on insulatorsl) Continuous harmonic currents in the power systemm) Unusual transportation or storage conditionsn) Untransposed lines

5. Operating and rating considerations

5.1 Introduction

Transmission line series reactance can be compensated by combinations of fixed series capacitors andTCSC banks (see Figure 1). TCSC banks use one or more controllable modules to achieve the range ofperformance requirements specified by the purchaser. This clause discusses requirements of TCSCoperating and rating considerations.

The TCSC circuit configurations discussed in this standard (see Figure 2) consider three basicoperating modes: a) thyristors ‘‘blocked’’ (no gating and zero thyristor current), b) thyristors‘‘bypassed’’ (gating resulting in 360� power frequency thyristor current), and c) ‘‘controlled’’ operation(periodic gating resulting in thyristor currents at a frequency higher than the power frequency). The‘‘controlled’’ operation modes discussed in this standard refer to operating conditions that vary thecapacitive reactance of the TCSC. ‘‘Controlled’’ operating modes that result in varying the inductivereactance are identified for reference only.

Steady-state waveforms for the basic TCSC circuit configuration operating in the capacitive range areshown in Figure 3. The capacitor voltage (VC) is plotted with two different control angles (a). Thisstandard defines the control angle (a) as the electrical angle from the capacitor voltage zero crossing tothe start of thyristor conduction. For steady-state conditions, the conduction interval (s) of thethyristor valve current (ITH) is symmetrical around the capacitor voltage zero crossing with VC laggingthe current (IC¼ ILþ ITH) that drives the capacitor voltage. Typical capacitor voltage and currentwaveforms with control angles at 180� and 145� are shown in Figure 3 a) and Figure 3 b), respectively.




WITHDRAWN


Figure 1—Typical TCSC installation nomenclature

NOTES

1—Segment (1f)2—Switching step or module (3f)3—Capacitor units4—Discharge current limiting reactor5—Varistor6—Bypass gap7—Bypass switch8—Additional switching steps when required

9—External bypass disconnect switch10—External isolating disconnect switch11—External grounding disconnect switch12—Thyristor reactor13—Bidirectional thyristor valve14—Controllable subsegment (1f)15—Additional controllable subsegments when required

Figure 2—TCSC controllable subsegment



WITHDRAWN The definition of control angle with reference to voltage zero is selected to be consistent with otherpower electronic equipment. It should be recognized, however, that most TCSC control systems usethe line current waveform as an important control reference.

As can be seen in Figure 3 b), when a subsegment is operating in the capacitive mode, a current in thethyristor branch can boost the power frequency voltage across the capacitor segment, resulting in aneffective capacitive reactance greater than the nominal (XORDER ’ 2.0). Note that the pulses of currentin the thyristor branch cause a distortion of the capacitor voltage (VC). In a TCSC application, theincreased capacitive reactance would increase the line current. Some comments on the units for themagnitudes of the voltages are in order. As previously mentioned, conduction of the thyristor branchdistorts the voltage across the subsegment. This distortion means that the voltage includes nonpowerfrequency components and that the relationship between RMS and peak voltage is not

ffiffiffi2

pas is the

case for a pure sinusoid. The relationships for these voltage quantities for various XORDER are shownin Table 1. The values assume one per unit line current and that the power frequency RMS voltageacross the subsegment with an XORDER of one is defined as one per unit.


��

�� α � �� α � ��

Figure 3—TCSC steady-state waveforms4 for control angle a and conduction interval s

Table 1—Peak and RMS voltage relationships

XORDERPower frequency(RMS voltage)

Power frequency(peak voltage)

Total RMS(voltage)

1.0 1.0 1.414 1.0

2.0 2.0 2.56 2.02

3.0 3.0 3.39 3.03

4The scales used in these figures are normalized for illustration purposes and are not in per unit of any set of rated parameters for

a subsegment.



WITHDRAWN 5.2 TCSC characteristics

Characteristics of TCSC are determined from the series capacitor (C) and reactor (L) circuitparameters shown in Figure 2. The steady-state TCSC power frequency reactance [X(a)] as a functionof thyristor control angle (a) can be calculated from Equation (1), based on an analysis of thyristorcurrent (Christl et al. [B3]; Jalali et al. [B16])5:

XðaÞ ¼ �j

oC1� k2

ðk2 � 1Þsþ sinðsÞ

�þ 4k2

ðk2 � 1Þ2cos2ðs=2Þ k tanðks=2Þ � tanðs=2Þ

�

" #ð1Þ

where

s is 2(�� a),a is the control angle from capacitor voltage zero,k is �/o,o is 2�f,f is the power frequency,� is 1=

ffiffiffiffiffiffiffiLC

p,

L is the inductance,C is the capacitance.

Equation (1) represents the reactance of the equivalent power frequency reactance of a TCSCcontrollable subsegment. The equation does not include the other components of impedance that theTCSC has because of the distorted voltage across the subsegment. Because the firing of the thyristorresults in a circuit that is not linear, the equation cannot be used to predict performance if the linecurrent is a combination of power frequency and other frequency currents. This equation cannot beused in the analysis of subsynchronous resonance.

The TCSC power frequency steady-state reactance characteristics of Equation (1) for ‘‘controlled’’operation in the capacitive range (a0< a< 180�) and inductive range (90� < a< a0) are shownin Figure 4. The magnitude of the inductance in the thyristor branch has some effect on thischaracteristic.


Figure 4—TCSC power frequency steady-state reactance characteristics

5The numbers in brackets correspond to those of the bibliography in Annex A.



WITHDRAWN The transition between the inductive and capacitive region has a resonant condition that cantheoretically lead to extremely large values of reactance if the subsegment is in steady-state operationand the control angle approaches a0. The exact angle (a0) at which resonance will occur is dependenton the magnitude of the inductance and capacitance of the subsegment. Although it is possible tooperate a TCSC during transient conditions at the firing angle (a0), in practice, steady-state operationwith a control angle near a0 shall be avoided because it is difficult to control the reactance and theequipment may be subjected to high voltages and currents. It is recommended that the purchaserspecify a maximum steady-state capacitive reactance XORDER for XM (see 5.3).

5.3 Basis for TCSC ratings

The basis for rating a TCSC is dependent on the supplier applying basic TCSC characteristics (see 5.1and 5.2) to establish operating parameters that meet specific objectives defined by the purchaser.Operational objectives can include SSR mitigation, power oscillation damping, current (power flow)control, reactance control, special protective features, or combinations of these (see 5.4 and 5.5).TCSC operating parameters associated with a single controllable subsegment are shown in Figure 5and Figure 6. While Figure 5 can be used for establishing TCSC equipment limits, Figure 6 is moreuseful when specifying power system operating parameters from an application point of view.

Figure 5 shows the basic TCSC equipment operating parameters of a single controllable subsegment.A triangular area of controlled operation is shown with time-dependent voltage and current limitsbased on practical constraints of the TCSC equipment. Since Figure 5 is a plot of voltage versus linecurrent, straight lines from the origin represent lines of constant reactance. The line labeled ‘‘XC atControl Angle a¼ 180�’’ represents the TCSC capacitive reactance with essentially no thyristorcurrent, and is shown to be equal to the power frequency reactance of the capacitor (C). When theconduction time (s) of the thyristor valve is increased, the resulting increase in VC raises the effectivepower frequency reactance of the TCSC, and the line of constant reactance is rotated counterclockwiseon the figure. The range of controlled capacitive reactance of the TCSC (XORDER) is a function ofthe TCSC voltage (VC) and line current (IL) with typical ranges up to three times the power


˚

Figure 5—TCSC voltage–current capability curves (single controllable subsegment)



WITHDRAWN

frequency reactance of the capacitor (XC) as represented by the line labeled ‘‘XM at Minimum ControlAngle (aM).’’

The lines of constant reactance for controlled operation do not extend all the way to the origin becausethe steady-state firing of a thyristor valve is not possible at very low thyristor valve voltages andcurrents. All thyristors have a minimum voltage below which firing is not possible. In addition, somethyristor valves have power supplies for the firing circuits that can place additional constraints on thefiring of the thyristor valve when the line current is low. The results are a TCSC that has a minimumline current (IMIN) and a minimum voltage (VMIN) below which valve firing may not be reliable. Thiscan have ramifications on the application and operation of the TCSC.

The TCSC equipment has voltage and current limitations that constrain the range of operation. Theability of a subsegment to operate with increased reactance is constrained by the ability of theequipment to withstand the associated voltage.

For continuous operation in the capacitive region, the constraint on voltage is established with respectto the rated continuous operating point specified by the purchaser [Equation (2)]:

VR ffi IRXR ð2Þ

where

IR is the maximum continuous power frequency RMS line current at which a reactance of XR isrequired,

XR is the maximum power frequency capacitive reactance that shall be achievable on a continuousbasis at a rated line current of IR,

VR is the power frequency RMS voltage across the subsegment for which the equipment is rated forcontinuous operation.

In some applications, rated continuous operation will be defined by the purchaser for the condition ofno thyristor valve conduction. This is likely to be especially true for installations where a TCSC isrealized from an existing fixed series capacitor bank. For this case, XR will be equal to XC. However, inthe general case, XR is not equal to XC. This general case is shown in Figure 5 by the dotted constantreactance line.


Figure 6—TCSC reactance–current capability curves (single controllable subsegment)



WITHDRAWN For continuous operation, the TCSC is constrained to operate within the continuous voltage (VR) andline current (IR) capability of the capacitors, varistors, thyristor reactors, and thyristor valves.In Figure 5, the horizontal line labeled VR represents one such constraint. Although controlledoperation can typically implement an XORDER anywhere between 1 and 3, if the resulting steady-statevoltage (VC) exceeds VR, the controller should automatically reduce the XORDER, within theequipment temporary and dynamic time constraints, until the capacitor voltage is �VR. Tosummarize, the TCSC should be capable of continuous operation within the area bounded by thevoltage rating (VR) of the equipment with XORDER ranges typically between 1 and 3.

Typical temporary overload capabilities of a TCSC (typically � 30 min) are determined by thearea (see Figure 5) limited by the temporary voltage rating (VT) with XORDER ranges between1 and 3. This overload rating is typically 1.35 to 1.5 times the rated voltage (VR) for the capacitors.IEEE Std 824-1994 indicates that such overloads can reasonably expected to be withstood by thecapacitors approximately 300 times over the life of the capacitors.

The TCSC dynamic overload capabilities (typically � 10 s) are determined by the area (see Figure 5)limited by the dynamic voltage rating (VD) with controllable voltages that approach the protectivelevel (VPL) of the varistors or other protective device. This upper limit on voltage (VD) is typically lessthan twice the rated voltage (VR) of the capacitors.

Operating the TCSC in the inductive region (see Figure 5) is shown as a straight line labeled ‘‘XB

During Bypass Operation’’ that represents the reactance of the thyristor reactor. The actual operatingrange extends far to the right, since the reactor could be required to withstand power system faultcurrents (IF).

For simplicity in this recommended practice, the constant-voltage lines in Figure 5 can be consideredto be lines of constant RMS voltage. As can be seen from Table 1, increasing XORDER results in aproportionate increase in the power frequency RMS voltage. However, the same is not true for thepeak voltage where the increasing voltage distortion results in less than a proportionate increase involtage. Since much of the equipment is more sensitive to peak rather than RMS voltages, this couldbe a factor in the final design of the equipment. Finally, the constant-voltage line illustrating theprotective level is in terms of peak voltage.

Figure 6 presents information similar to that portrayed in Figure 5 except that the vertical axis on thegraph is reactance rather than voltage. The region of continuous capacitive reactance operation isshown in the shaded area. The lower reactance boundary is the fundamental frequency reactance (XC)of the capacitor. The upper reactance boundary (XM) is typically an XORDER of less than 3. The curvedboundaries represent the TCSC temporary and dynamic time constraints on the XORDER that arerequired to limit the voltage across the TCSC to the rated voltage of the capacitors. The left boundaryis the minimum line current (IMIN) for which the thyristors can reliably fire.

From an application perspective, the TCSC can be operated anywhere in the region of continuousoperation to enhance or control steady-state current (power) flow on the system. The TCSC can beoperated in a constant reactance or constant current (power) transfer mode.

Figure 6 shows an expanded area of temporary operation wherein the TCSC can utilize the 30-mintemporary overcurrent (IT) and overvoltage (VT) capability of the capacitors (typically between 1.35and 1.5 times VR). This capability is available to allow the TCSC to maintain its reactance at higherthan continuous rated currents or to allow it to increase temporarily its reactance in response tochanging power system conditions.

During dynamic conditions (typically �10 s) the TCSC can operate anywhere within the mostexpansive boundaries of Figure 6. This is an area of operation that is important in TCSC applicationsinvolving power oscillation damping. Care shall be taken in applying the results of




WITHDRAWN power system stability analysis programs when defining the dynamic requirements for a TCSC. Somesystem stability analysis programs model a TCSC simply as a variable reactance and do not have time-dependent constraints on the maximum voltage as is the case with a practical TCSC (see Annex B).

Also shown in Figure 6 is the horizontal line illustrating TCSC operation in the inductive bypassregion (XB) with continuous (360�) thyristor valve conduction.

5.4 Duty cycle

5.4.1 Introduction

The purchaser should specify the required sequences of faults, dynamic overload, temporary overload,and continuous currents for the TCSC bank. These sequences form the duty cycles that all of thecomponents of the TCSC bank should be designed to withstand. The duty cycle should be consistentwith the manner in which the surrounding power system will be operated for both internal andexternal line faults. The purchaser should define duty cycles for faults of normal and extendedduration and for faults of different types (multiple and single phase). The terms normal and extendedrefer to the operation of the line relays and line circuit breakers. A normal fault duration is thatassociated with the correct operation of the primary line relaying and the line circuit breakers. Anextended fault duration is the longer time that can occur when the fault is not detected by the primaryrelays or there is a failure of a line circuit breaker.

The purchaser should specify the power system fault currents, the type of bypass that can occur duringinternal and external faults, and the desired post-fault control mode(s), reactance range, and voltageacross the TCSC bank:

a) Fault currents should be defined in terms of the parameters of the transmission line in series withthe TCSC bank and the equivalent short-circuit impedance at the terminals of that line for thesurrounding power system. In applications where the power system parameters can change overtime, the purchaser should clearly identify the specific set of parameters for which the equipmentis to be designed. The purchaser should specify that the supplier designs the equipment for theworst fault locations on the power system. Consideration should be given to the condition of aparallel line out-of-service that can result in a temporary increase in the TCSC line current.

b) The duration of internal and external faults should be defined for all fault types. The reclosingtime for internal and external faults shall be defined. The type of line reclosing (single phase orthree-phase) should also be defined whether simultaneous or nonsimultaneous reclosing isapplied.

c) There are four possible means of bypassing the capacitors of a TCSC during a power systemfault: thyristor valve, varistors, bypass gap, and bypass switch. The purchaser should specify thedesired type of bypass that should be used for various power system fault conditions.

d) The performance of the TCSC following fault clearing can be critical to the stability of thepower system. In addition, the thyristor junction temperature (see Clause 6) can be elevated dueto conduction during the fault. Therefore, it is important that the desired post-fault range ofreactance and voltage across the TCSC be carefully specified.

5.4.2 Duty cycle sequence

The following are examples of duty cycle sequences that should be specified for a TCSC bank. Thesesequences are different for external and internal line section faults. Presented are possible modes ofoperation for various overvoltage protection schemes for the TCSC bank. The purchaser should tailorthe sequences to the requirements for the specific application. The equipment should be able to execute




WITHDRAWN the specified duty cycle at any ambient temperature within the range specified by the purchaser.Further clarifications on duty cycle sequences are given in Annex C.

5.4.2.1 External line section faults

Examples of TCSC bank duty cycles for external faults of normal duration are described below.External faults are faults on the power system at locations other than on the transmission lineassociated with the TCSC bank being specified.

a) A varistor is the primary overvoltage protection:

1) The TCSC is initially in the inserted condition with rated continuous current (IR) and thethyristor valve operating in a conduction mode consistent with the objectives specified bythe purchaser that results in the highest thyristor operating junction temperature.

2) An external fault occurs that is cleared within normal clearing time. The varistor is requiredto withstand the duty associated with protecting the capacitors and thyristor valve duringthe fault. Bypass with the thyristor valve during all or part of the fault duration ispermitted. However, bypass with a bypass gap or switch is not permitted. Within one cyclefollowing fault clearing the thyristor valve shall be able to operate in a conduction modeconsistent with the power transfer objectives of the purchaser. The only exception is thatthe varistor and/or the thyristor valve may conduct as required to limit the voltage acrossthe TCSC to the protective level (VPL).

3) The TCSC is exposed to swing current and overload currents followed by post-fault currentsthat can be greater than IR as a result of changing power system conditions. The purchasershall specify the magnitude of the post-fault overload currents. It may be at rated current (IR)or at the 30-min overload current (IT) followed by rated current (IR). During this period, theequipment shall be able to achieve the 10 s and 30 min overload objectives of the purchaser.Consideration shall be given to the energy the varistor can absorb during the swing.

4) The TCSC returns to operation at rated current (IR) and with the thyristor valve operatingin a conduction mode consistent with the objectives specified by the purchaser.

b) The thyristor valve is the primary protection:

1) The bank is initially in the inserted condition with rated continuous current and the valveoperating in a conduction mode consistent with the objectives specified by the purchaserthat results in the highest thyristor junction operating temperature.

2) An external fault occurs that is cleared within normal clearing time. The thyristor valveshall conduct as required to limit the voltage across the capacitors to less than or equal tothe protective level (VPL). Closure of the bypass switch is not permitted. Within a few cycles(time to be specified by the purchaser) following fault clearing, the valve shall be able tooperate in a conduction mode consistent with the power transfer objectives of thepurchaser. The only exception is that the thyristor valve may conduct as required to limitthe capacitor bank voltage to the protective level (VPL).

3) The TCSC is exposed to swing current and overload currents followed by post-faultcurrents that can be greater than IR. The purchaser shall specify the magnitude of the post-fault overload currents. It can be at rated current (IR) or at the 30-min overload current (IT)followed by rated current (IR). The equipment shall be able to achieve the 10 s and 30minoverload objectives of the purchaser. Consideration shall be given to the selected protectivelevel (VPL) and the capabilities of the thyristor valve to ensure that the thyristor valve caninsert the capacitors during overload conditions and achieve the desired power transferobjectives. This shall be possible in spite of the additional components of voltage that canappear across the capacitors due to reinsertion by the thyristor valve. Reinsertion duringthe overload can result in a total voltage across the capacitors and the thyristor valve thatapproaches twice that associated with the overload current, leading to voltage triggeringand failure to reinsert unless counteractive thyristor valve control strategies areimplemented. In practice, the reinsertion transients are limited by a metal oxide varistor




WITHDRAWN in parallel with the valve. The voltage–current characteristic of the varistor shall becarefully coordinated with the protective level established by the valve to avoid excessiveenergy absorption by the varistor. Simulations shall be performed to establish the energyrequirements of the varistor for power system faults and swings.

4) The bank returns to operation at rated current (IR) and with the thyristor valve operatingin a conduction mode consistent with the objectives specified by the purchaser.

5.4.2.2 Internal line section faults

Examples of duty cycles for normal internal faults are described in a), b) and c). Internal faults arefaults on the power system at locations on the transmission line associated with the TCSC bankspecified by the purchaser.

a) Varistor is primary protection with gap bypass:

1) The TCSC is initially in the inserted condition with rated continuous current (IR) and thethyristor valve operating in a conduction mode consistent with the objectives specified bythe purchaser that results in the highest thyristor junction operating temperature.

2) An internal fault occurs. Bypass with the varistor, the thyristor valve, the bypass gap, orbypass switch is permitted. The varistor shall withstand the duty that occurs prior tocompletion of the bypass. The thyristor valve, the bypass gap, and/or switch shallwithstand the resulting capacitor discharge and power frequency fault current. The linecircuit breakers interrupt the fault. The thyristor valve shall withstand any prolongedcurrent associated with the transfer of current from the thyristor valve to the bypass switch.

3) The line remains open until it is reclosed within the time specified by the purchaser. TheTCSC shall reinsert within the time specified by the purchaser. The speed of recovery of thedielectric voltage withstand of the gap shall be consistent with the required reinsertion time.The thyristor valve shall thermally recover sufficiently to achieve the post-fault operationalrequirements of the purchaser.


b) Varistor is the primary protection with thyristor valve bypass:


2) An internal fault occurs. Bypass with the varistor, the thyristor valve, and (optionally) thebypass switch is permitted. The varistor shall withstand the duty that occurs priorto completion of the bypass. The thyristor valve and/or bypass switch shall withstandthe resulting capacitor discharge and power frequency fault current (IF). The linecircuit breakers interrupt the fault. The thyristor valve shall withstand any prolongedcurrent associated with the transfer of current from the thyristor valve to the bypass switch.

3) The line remains open until it is reclosed within the time specified by the purchaser. TheTCSC bank shall reinsert within the time specified by the purchaser. The thyristor valveshall thermally recover sufficiently to achieve the post-fault operational requirements of thepurchaser.


c) Thyristor valve is the primary protection and fault bypass device:


2) An internal fault occurs. Bypass with the thyristor valve and (optionally) the bypass switchis permitted. The thyristor valve and/or bypass switch shall withstand the resulting




WITHDRAWN capacitor discharge and power frequency fault current (IF). The line circuit breakersinterrupt the fault. The thyristor valve shall withstand any additional current associatedwith the transfer of current from the thyristor valve to the bypass switch.

3) The line remains open until it is reclosed within the time specified by the purchaser. TheTCSC shall reinsert within the time specified by the purchaser. The valve shall thermallyrecover sufficiently to achieve the post-fault operational requirements of the purchaser.

4) The TCSC returns to operation at rated current and with the valve operating in aconduction mode consistent with the objectives specified by the purchaser.

5.4.2.3 Faults of extended duration

In a manner similar to that illustrated for normal faults, the purchaser should define the duration andsequence for extended clearing of faults and the performance requirements of the TCSC bank for suchconditions. The emphasis may be on extending the performance requirements for the TCSC bank if itis critical to the power system or conversely, allowing the bank to bypass in a protective mode to limitthe stress on the equipment. In any case, the purchaser should define the maximum external faultduration following which the TCSC bank is expected to resume rapidly its operation as a controlledseries capacitor. For longer fault durations, the bypass switch is permitted to close. For an internalfault, the bypass switch should be permitted to close for any extended fault and reinsertion delay.High-speed line reclosing is not normally enabled following extended fault clearing.

5.5 Operational objectives

Application studies should be performed during the conceptual, specification, design and operatingstages of a series compensation project to resolve technical issues related to steady-state, temporary,and dynamic operating conditions of a TCSC installation (CIGRE Working Group 14.18 [B4]; IEEEFACTS Working Group [B15]). These studies require careful planning and coordination to ensurethat the operational objectives of the TCSC are met by the specified equipment. This requires thatappropriate computer models for the transmission system and TCSC controller are established andchecked to validate study results (see Annex B). Operational objectives that may be the motivation fora TCSC application include the following:

a) Subsynchronous resonance (SSR) considerations: Fixed series compensation inserted into atransmission line may produce a resonant circuit combination that can, under certain conditions,excite mechanical oscillations in turbine generators connected to the system. These mechanicaloscillations can, in turn, further excite the electrical system at subsynchronous frequencies thatmay increase to the level where generators can be damaged. This SSR phenomenon is a significantconcern in planning fixed series capacitor installations and requires extensive study efforts toidentify potential problems and solutions. An advantage of TCSC technology is that atsubsynchronous frequencies, the TCSC will provide a degree of SSR mitigation when operatedwith anXORDER greater than 1. The TCSC can helpmitigate the resonant SSR series combinationthat results from fixed series capacitors. Detailed studies of the power system are required todetermine an appropriate design for SSR mitigation. Extensive digital computer simulationstudies, transient network analyzer (TNA) testing, and field measurements have verified theinherent SSR mitigation features of TCSC installations when properly designed (Cope et al.[B5];Othman and Angquist [B19]; Pilotto et al. [B22]; Piwko et al. [B23]) and applied.

If the TCSC application requires that SSR concerns be addressed, it is recommended that studiesbe performed involving detailed models of the power system, the nearby turbine generators, andthe TCSC. This recommendation is heightened in situations where the power systemwill include acombination of fixed series capacitors and TCSC, and the combined series compensation exceeds35%. If the studies indicate that fixed series capacitors with the desired level of compensation willresult in an SSR problem, the SSR studies should have the active involvement of the TCSCsupplier.




WITHDRAWN The TCSC can only provide SSR mitigation if the valves are firing on a continuous basis. Thedegree of mitigation can be a function of the control angle. The result is that, for the TCSC tomeet the SSR mitigation objectives, its operating region shall be constrained to an XORDER equalto or greater than the minimum value determined by power system studies. For example, inFigure 5, if the mitigation of SSR requires that the XORDER be greater than that depicted as XR,then the usable range of operation is the segment between XR and XORDER equal to 3. Also, it isclear that for this type of application the rated reactance for the TCSC shall beXR rather thanXC.In an application where SSR mitigation is critical, the operation of the TCSC under low linecurrent condition shall be reviewed. For line currents below which reliable valve firing is notpossible, the TCSC shall be bypassed via the bypass switch.

b) Power oscillation damping (POD) control: POD is a specialized subset of closed-loop reactancecontrol that can be realized by modulating the TCSC reactance in response to transmissionsystem conditions to dampen power system oscillations (Gama et al. [B8]). Supplemental inputsignals, such as frequency or line current, related to the power swings need to be provided to theTCSC controller with the proper gain and phase-angle relationship required for damping. TheTCSC installation, if used correctly, can enhance stability and damp interarea power swings onthe ac system. The TCSCs that have been applied for power oscillation damping have had arated reactance that is greater than XC so that the reactance can be increased and decreased toachieve the desired damping at rated line current.

The current swings of the system interacting with the modulation of the TCSC reactance by thePOD create oscillating voltages across the TCSC. The voltage constraints of the TCSC (VD)override an unacceptable reactance order; therefore, it is imperative that the system studiesproperly account for this limitation (as discussed in Annex B).

c) Transient stability: The ability to control TCSC reactance rapidly provides a means to enhancesystem dynamic performance. Typically, a TCSC will have a basic control that will hold aspecified reactance order, within the device design limits. Higher-level control inputs to thereactance control can be used to achieve improvements in: 1) transient angle stability, 2) post-contingency current (not necessarily on the line with the TCSC), and 3) transient voltagestability. This may be implemented to control the fundamental frequency reactance of eachphase independently or control an average three-phase value within reactance unbalance limitsestablished by design criteria. Capacitive reactance ranges between XC and XM can be controlledwithin the protective limits of time-dependent voltage and current ratings of the TCSCequipment. These transient stabilizing control signals are most commonly implemented as open-loop discrete switching orders (e.g., condition-based discrete actions of the type commonly usedin remedial action schemes). Closed-loop (e.g., continuously acting control actions withfeedback) implementation is also possible.

Detailed power system load flow and stability studies (see Annex B) are normally required todevelop appropriate algorithms and settings for specific applications. It is important that theTCSC be specified to have the necessary dynamic current, reactance, and voltage capabilities asdetermined in transient stability studies of the power system. It is important to recognize thatthe TCSC model used in such studies may not have the voltage constraints (VD) that the actualequipment will have. As with the application of fixed series capacitor banks, the application ofTCSC shall address the higher performance requirements of the power system during temporaryand dynamic overloads on the power system. As with conventional series capacitors, TCSCequipment has higher temporary and dynamic overload ratings that can provide thisperformance. These overloads are shown in Figure 7, which illustrates the current through aTCSC during an external fault and disconnection of a parallel transmission line. However, inthe case of fixed series capacitors, this additional capability can only be used if the inherentswings of the power system impose overloads on the bank. That is not the case with the TCSC.Since the TCSC can adjust its reactance, the overload capability of the equipment can be used




WITHDRAWN

to the degree defined in Figure 7, even if the line current does not exceed the continuous currentrating (IR).

d) Current or power control: The TCSC can be used to regulate either line current or throughpower on a continuous or emergency basis. A closed-loop regulator can be used on each phase oran average three-phase value to regulate transmission line current (IL) (or power) within a limitedrange dependent on the power transmission system and TCSC operating parameters. Theseregulators are slow and shall be coordinated with the transient and POD controls.

e) Voltage control: Like static var compensators (SVCs), TCSCs can be used to control the voltageat a specific point in the power system. This voltage control can improve voltage stability andreduce voltage fluctuations, including flicker. A closed-loop regulator can be used to modify theTCSC reactance order in response to a measured voltage signal.

f) Phase balancing control: Phase balancing to compensate for asymmetrical currents as a result ofsingle-phase loads or untransposed lines can be achieved by regulating the control angle foreach phase independently, resulting in current balancing. This feature may be realized in thereactance or current control modes. Design of this feature requires detailed three-phaserepresentation of the TCSC and the surrounding power system.

6. Thyristor valves (bidirectional)

6.1 Current and voltage capability

The current and voltage capabilities of the thyristor valve are derived from the TCSC ratings asdiscussed in 5.3 and illustrated in Figure 5 and Figure 6. These ratings determine the power frequencycomponent of the voltage, VC, which is being inserted by the TCSC in series with the transmission line,at different amplitudes of the line current power frequency component, IL. In the design procedure it isassumed that the line current remains sinusoidal (undistorted) at the rated power frequency.

6.1.1 Current capability in normal TCSC operation

The design procedure often starts with selection of the capacitance, C, of the series capacitor bank andthe inductance, L, of the TCSC reactor. The angular frequency � of the resonance circuit in the TCSC


Figure 7—Current capability of TCSC



WITHDRAWN can be calculated as described in 5.2, Equation (1). In Equation (1), k was introduced as the ratiobetween � and the network frequency o:

� ¼ 1ffiffiffiffiffiffiffiLC

p

k ¼ �

o

Typically, k has a value in the range 2.5–3.5. It takes a lower value in applications that require a highmaximum XORDER, e.g., in power oscillation damping applications. Once k has been determined, therequired current capability of the thyristor valve can be obtained by translation of the TCSC ratingcurves, according to Figure 6, into thyristor currents. The current capability requirements shall beconsidered both for the capacitive (controlled reactance) mode of operation and for the bypass mode.The calculated thyristor junction temperature should be within acceptable limits for all specifiedloading and fault duty cycles agreed upon between the purchaser and the supplier.

6.1.1.1 Thyristor current in capacitive controlled reactance mode

Equation (3) and Equation (4) apply for the average and RMS value of the current, ITAV and ITRMS,respectively, passing through the thyristor valve in each direction:

ITAV ¼ k2

k2 � 1

IIL�

1

kcos

s2

� �tan

ks2

� �� sin

s2

� �� ð3Þ

ITRMS¼k2

k2�1IIL

�

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffis4�

1þsinss

þ 1þcoss1þcosðksÞ 1þsinðksÞ

ks

� ��4

coss2

� �cos

ks2

� � sinkþ1ð Þs

2

� �ðkþ1Þs þ

sink�1ð Þs

2

� �ðk�1Þs

2664

3775

8>><>>:

9>>=>>;

vuuuuutð4Þ

where

s is the angle corresponding to the conduction interval as shown in Figure 3b),IIL is the peak value of the fundamental power frequency component of the line current (IIL ¼ IL

ffiffiffi2

p).

Using Equation (3) and Equation (4), the conduction losses in each thyristor can be calculated asshown in Equation (5):

PT,cond ¼ uT0ITAV þ rTI2TRMS ð5Þ

where

uT0 is the thyristor threshold voltage,rT is the thyristor slope resistance.

The maximum junction temperature in the thyristor can now be calculated based on:

a) The thyristor losses related to the conduction current as given previously.b) Additional losses related to the turn-on and turn-off processes; the calculation can be performed

using a similar approach to the one described in IEEE Std 1031-2000 for SVC thyristor valves.c) The thermal resistance between the thyristor junction and the coolant.d) The maximum coolant temperature.




WITHDRAWN 6.1.1.2 Thyristor current in bypass mode

In bypass operation, the thyristor valve is continuously conducting. The thyristor valve current issinusoidal and consists of the line current plus an additional current circulating between the capacitorand the thyristor branch reactor. The RMS current through the thyristor valve (see Figure 2) is givenby Equation (6):

ITH ¼ k2

k2 � 1IL ð6Þ

The corresponding average and RMS values, ITAV and ITRMS, respectively, for the thyristor valve ineach direction are given by Equation (7) and Equation (8):

ITAV ¼ k2

k2 � 1

IIL�

ð7Þ

ITRMS ¼ k2

k2 � 1

IIL2¼ k2

k2 � 1

ILffiffiffi2

p ð8Þ

The turn-on and turn-off losses may be neglected in this case.

6.1.1.3 Current capability at internal faults

The thyristor valve should be designed to carry the fault current passing through the valve for linefault cases specified by the purchaser. When the fault appears and the thyristor valve is commanded toenter the bypass mode, an oscillatory capacitor discharge current adds to the fault current from theline passing through the valve. The amplitude and the duration of the thyristor valve current dependon the protection system philosophy.

Usually, the highest currents passing through the thyristor valve relate to short circuits in the line inwhich the TCSC is installed (internal faults). It is necessary that the thyristor valve has the capabilityof conducting the full short-circuit current during the first half cycle following the fault inception asthe thyristor can be in its conductive state when the fault occurs. During the remaining duration of thefault, different principles may be utilized:

a) The thyristor valve continues to carry the fault current:The thyristor valve may be used to bypass the capacitor at line faults preventing a heavy currentfrom passing through the capacitor. In a first design approach, the thyristor valve is designed tocarry the full fault current during the maximum time required to close the mechanical bypasscircuit breaker. Using this approach, it is required that the reliability of the devices that commandthe thyristor valve to enter and to remain in its bypass mode (i.e., to be continuously conductingas stated in 5.1) during the fault is being secured. Further, if separate inductors are used for thethyristor valve and for the bypass circuit breaker, means to prevent or to grant sufficient dampingof ‘‘trapped current’’ should be provided. As the valve remains in a conducting state during thewhole fault time, no voltage stress is being imposed on the thyristor valve. This means that thesurge current may be determined by the maximal temperature in the thyristor junction, whichshould not exceed the destructive level (somewhere in the region of 300 �C).

b) The fault current is commutated into a parallel bypass gap:When the fault current is high, it may be desirable to commutate the fault current into anotherparallel branch in order to unload the fault current from the thyristor valve much faster thanwhat can be achieved by a mechanical bypass circuit breaker. In fixed series capacitorinstallations, bypass gaps are frequently used for this purpose. It may also be used in TCSCapplications. The bypass gap can be initiated in a few milliseconds. However, in order to turn onthe bypass gap, the capacitor voltage must be sufficiently high. When the TCSC is operatingin capacitive boost mode or in bypass mode, the valve repeatedly is in its conductive state.If the fault is initiated when this is the case, the corresponding thyristor valve cannot be blocked,




WITHDRAWN but the thyristor shall continue to carry the fault current until a zero crossing occurs. In order totrigger the bypass gap, the thyristor should block voltage so that the capacitor voltage becomessufficiently high. This means that the thyristor valve surge current stress should be kept below alevel that permits a reverse blocking voltage to appear across the thyristor valve following thefault current. The problem of preventing or damping ‘‘trapped current’’ should also beconsidered in this case.

6.1.1.4 Current capability at external faults

Faults that appear on lines other than the one in which the TCSC is installed are external faults. Oftensuch faults cause line currents to exceed the maximum line current in the operational range of theTCSC. In such cases, it may be permitted to bypass the TCSC valve during the fault duration. It isnecessary that the TCSC can be reinserted as soon as the line current drops and enters the normaloperational range. The reinsertion can take place under overcurrent conditions (short-time currentrating as indicated in 5.4), if specified. Accordingly, the current capability of the thyristor valve shallbe sufficient to carry the bypass current during the fault time without causing a temperature rise in thethyristor that is prohibitive with respect to the fast reinsertion of the TCSC. It should be noted that thevalve shall carry the capacitor discharge current appearing at initiation of the bypass operation, inaddition to the fault current from the line.

6.1.2 Voltage capability

The voltage rating of the TCSC valve is derived from the capability curves as depicted in Figure 5 andFigure 6. In these curves different thyristor valve voltages have been defined for rated (continuous)operation (VR), for temporary overload (VT), and for dynamic overload (VD). Normally, thecontinuous operation requirement dictates the ‘‘protective voltage level,’’ VPL, of the varistors that areconnected in parallel with the capacitor bank. The protective voltage is the maximum instantaneousvoltage that occurs across the varistor in any fault case. Typically, the protective level is about 2 to 2.5times the peak voltage at continuous rating [Equation (9)]:

VPL ¼ K1ð Þ � VVC ¼ K1ð Þ � VC

ffiffiffi2

pð9Þ

where

K1 ¼ 2 to 2.5.

If the requirements on temporary or dynamical overload are severe, a higher protection factor can benecessary. The varistor limits the voltage across the thyristor valve to the protective voltage level VPL

in the off-state.

In designing the voltage capability of the valve, it is also necessary to consider the overvoltage, whichoccurs at turn-off. Figure 8 depicts the typical appearance of a thyristor voltage in a TCSC operatingin phase-controlled capacitive boost mode.

The maximum thyristor voltage depends mainly on the capacitor voltage, VC,turn-off, at turn-off plus anadded thyristor turn-off voltage, �VT,turn-off, which depends on the current derivative at turn-off. Thelatter is a function of the former as shown in Equation (10):

diV,turn-off

dt¼ �

VC,turn-off

Lð10Þ

where

L is the thyristor branch inductance,iV is the valve current.




WITHDRAWN

In the voltage–current capability curves in Figure 5, it has been assumed that the dynamical overloadarea is limited by a maximum constant voltage (the upper horizontal line in the diagram) for a range ofline currents. Such a limit is motivated by consideration of the voltage capability of the capacitor. TheXORDER varies along this limit, and it increases inversely proportional to the line current. Accordingly,the turn-off voltage and the current derivative increases when the line current decreases along theconstant voltage limit. The highest thyristor valve turn-off voltage thus appears on the left-hand-sideend of the upper limiting line in Figure 5. Depending on the required operational capability curves andon the main circuit layout, the turn-off voltage can be higher or lower than the maximum protectiveoff-state voltage defined by the varistor.

A maximum turn-off voltage, Vmax,turn-off, should be determined for the thyristor valve design. Thisvoltage should be higher than the turn-off voltage in the steady-state, when the TCSC is operating atany point within the capability diagram. Measures in the control system should prevent turn-on fromoccuring, resulting in turn-off voltages exceeding Vmax,turn-off.

Overvoltage protection at turn-off of the valve may be arranged by different approaches. Someexamples are

— Individual protective firing implemented for each thyristor.— Measuring system arranged across the whole valve commanding overriding trigger pulses at

overvoltage.— Measuring system supervising the thyristor branch di/dt and commanding overriding trigger

pulse when the current slope exceeds the design level.

6.1.2.1 Voltage rating of semiconductor stack, normal operation

When the maximum thyristor valve voltages with respect to the varistor protective level and themaximum thyristor turn-off voltage have been determined, the valve can be designed. When selectingthe number of devices and the voltage rating, the following factors should be considered:

— The maximum valve voltage Vvalve.— Margin with respect to turn-off voltage limitation.


Figure 8—Thyristor valve voltage in a TCSC



WITHDRAWN — Margin with respect to voltage sharing between the individual devices in the string due to

deviations in recovery charge.— Required redundancy in the number of series-connected semiconductor devices.

6.1.2.2 Voltage rating of semiconductor stack, fault cases

If the protection system utilizes a bypass gap, which requires a high sparkover voltage, the thyristorwithstand voltage following a surge current shall be considered. If the protection system utilizescontinuous bypass, no specific voltage capability requirement for fault cases is applicable.

6.2 Valve control

6.2.1 Triggering system

The valve base electronics (VBE) subsystem is an interface between the TCSC control system for asubsegment and the platform-mounted thyristor electronics (TE) subsystem, as shown in Figure 9 a).


Figure 9—Valve base electronics (VBE) and thyristor electronics (TE)



WITHDRAWN Firing logic is received from the subsegment control system, and a thyristor valve trigger pulseis generated via fiber optics to the TE. Additionally, status information on each subsegment thyristorlevel is received from the TE and sent to the TCSC control system thyristor monitoring subsystem.

The thyristor valve protection, resistive-capacitive snubbers, and power supply for the TE are locatedon the platform at the thyristor level where a firing pulse is generated for each thyristor, as shown inFigure 9 b).

6.2.1.1 System aspects

Both electrically triggered thyristors (ETT) and direct light-triggered thyristors (LTT) can be used forTCSC. The following requirements apply to the valve control system independently of the type ofthyristors. It shouldbe possible tofire the thyristors during all applicable operating conditions in order to:

— Control the valve during normal operating conditions in capacitive boost mode and bypass mode.— Control the valve in order to bypass the series capacitor during system faults.— Make sure that the valve will not be blocked in a situation that would cause dangerous voltage

across the valve.— Make sure that the valve will not be blocked in a situation where the thyristors have had no time

to recover after previous conduction.

6.2.1.2 Normal operating conditions

It should be possible to control the valve in the whole operating range of interest. Valve triggeringat low voltage is likely to occur at low line currents, or with low boost factors in capacitive boostmode.

6.2.1.3 Valve triggering during system faults

Thyristor triggering at the capacitor voltage protective level may be required during system faults inorder to avoid overloading of the varistor. In this case, a thyristor valve triggering results in a totalvalve current that is the sum of the capacitor discharge current and the fault current through theTCSC. Blocking of the valve during these conditions would lead to thyristor overvoltage. Therefore,the valve should remain conducting. It should be noted that the thyristors shall always be designed tohandle the fault current independently of fault-handling strategy because a system fault can occurwhen the thyristor valve is conducting.

In situations with system faults and high current derivatives in the thyristor valve current, it is essentialthat the thyristor triggering system is fast enough to prevent high voltage to build up across thethyristors when the current passes through zero.

6.2.2 Protections and control system functions

The following functions are discussed:

— Maximum triggering voltage during normal operation— Current derivative (di/dt) protection— Thyristor recovery protection— Thyristor protective firing— Actions at low line current

6.2.2.1 Maximum triggering voltage during normal operation

The purpose of this function is to make sure that the thyristor valve will not be triggered insituations that would cause thyristor valve turn-off voltages to exceed the design level during normal




WITHDRAWN operation. This function prevents unintended intervention of the thyristor valve overvoltageprotection.

6.2.2.2 Current derivative (di/dt) protection

This is an indirect thyristor valve overvoltage protection. The purpose of this function is to protect thethyristor valve from blocking in situations that can cause too high voltage across the thyristor valve.The protection measures the current through the thyristor valve, and orders continuous pulses to thethyristor valve if the current derivative exceeds a set level.

6.2.2.3 Thyristor recovery protection

The purpose of this protection is to prevent partial turn-off of the thyristor valve in case of shortrecovery time followed by reapplied forward blocking. The full-reapplied voltage can appear across onesingle thyristor position, which shall be fired by the recovery protection. The maximum derivative of thereapplied forward voltage depends on the maximum instantaneous line current that charges the maincapacitor. This means that the voltage derivative is normally limited to the range 150–300V/ms.

6.2.2.4 Thyristor protective firing

An overvoltage protection can be used that senses the voltage across individual thyristors and sends afiring pulse to the thyristor, if the voltage exceeds a certain level.

6.2.2.5 Actions at low line current

The TCSC cannot remain operating in capacitive boost mode when the line current becomes very low,typically in the range of one tenth of the rated line current. There are two reasons for this:

a) The measuring system has a limited resolution and noise suppression capability. Therefore, theresponse signals become too inaccurate for the control system.

b) The auxiliary power used for thyristor triggering is often being picked up from the main circuit.When the line current becomes too low, this power supply fails and the thyristors cannot betriggered.

When the line current is low, the corresponding fundamental power frequency component of theinserted capacitor voltage is also low. In this condition, the power flow in the line depends very little onwhether or not the series capacitor is inserted or bypassed. However, from a subsynchronousresonance (SSR) point of view, it could be important that the operating mode of the TCSC is welldefined, either in bypass mode or blocking mode.

If the low line current is sustained for a certain period of time, the control system can be designedeither to block the thyristors entirely or to close the mechanical bypass circuit breaker. Normaloperation should automatically be started when the low line current condition disappears.

From the equipment protection standpoint, low line current appears to be harmless. When auxiliarytriggering power is being picked up from the main circuit, it is important that the system is sufficientlyfast acting so that the thyristors can be triggered in order to prevent an overvoltage in case a suddenvoltage rise would occur across the capacitor. Triggering power to LTT can be provided at any timefrom ground potential.

6.2.3 Monitoring

The valve control system should have monitoring systems that allow indication of the number of thefaulty thyristor positions per phase. These indications should be available from the operatorworkstation.




WITHDRAWN 6.3 Valve cooling system

The purpose of the thyristor-valve cooling system is to remove the heat produced by the thyristorvalve. Generally, two types of thyristor cooling systems are possible: water-cooled systems or air-cooled systems. In either case, the cooling system should be completely furnished with all necessaryinterconnecting piping, ductwork, circulating pumps, blowers, heaters, make-up reservoirs, heatexchangers, filters, water treatment plant (if required), instrumentation, automatic controls, alarms,control power systems, and other necessary equipment. For normal TCSC applications, only liquidcooling is applicable.

6.3.1 Liquid cooling

The heat transfer from the closed liquid system to the ambient should take place in a water-to-air orwater-to-water heat exchanger. Some important requirements for the cooling system are as follows:

a) Redundant pumps: One pump is normally operating and a redundant pump is standing by.Should a pump failure occur, the second pump should automatically switch in without shuttingdown the equipment. There should be a pump changeover to allow automatic cycling of thesecond pump every month or so. Alarms should be displayed at the appropriate local andremote control cabinets to alert the operator that a pump problem exists.The cooling system should be designed to permit work on the defective pump unit withoutshutting down the TCSC.

b) Purification system: The purification system should be designed to maintain the resistivity of thewater above 1M�-cm. A resistivity transducer located in the outgoing water from the deionizershould detect the depletion of the material. The second purifying loop will continue to operatein the presence of a primary-loop alarm until its deionizer is depleted.

c) Antifreezing: If a low ambient outdoor temperature is specified, the water can be mixed withglycol in order to avoid freezing of the coolant.

d) Replacement: Filters and deionizer material should be designed to allow replacements in arelatively short time without shutdown of the cooling unit. (Normal replacement should not berequired more than once every 12 months.)

e) TCSC isolation: Deionized water is used for thyristor valve cooling due to the potentialdifference between ground and valve position. The TCSC should not be energized withoutcirculating the cooling water for prolonged periods of time. During such a condition, theconductivity of the water cannot be guaranteed.

6.4 Mechanical design

6.4.1 Valve housing

A TCSC has different environmental requirements for the thyristor valve compared to SVC andHVDC installations. The thyristor valve is located on an outdoor-insulated platform at high-voltagepotential. The thyristor valve shall, therefore, be housed inside an adequately designed valve housing.The valve housing should be properly electrically designed regarding insulation. It should belightweight, weather proof, and easy to maintain.

The specially designed thyristor valve housing should fulfill the following requirements:

a) Temperature: Since the valve housing is located outdoors, the housing will be exposed to the fulltemperature range specified for outdoor equipment. The thyristor units normally have anallowed operating range from a few degrees Celsius and upward. This means that the valve




WITHDRAWN cooling system shall include heaters for start-up of the thyristor valve at low temperatures incold climates.

b) Humidity: Depending on site conditions, different means to control the humidity in the valvehousing could be required. In climates with high humidity, dedicated equipment to reduce thehumidity in the air in the valve housing and communication insulator should be used. In areaswith less humidity, sufficient circulation of the air can be sufficient. This can be achieved byactive or passive air circulation. The risk of condensation shall also be considered, e.g., duringlarge sudden deviations in temperature.

6.4.2 Communication insulator

The communication insulator is required to transport the cooling medium to and from the thyristorvalve on potential. The insulator can also be used for the optical fibers for communication with thevalve and other equipment on the platform. The valve housing, the communication insulator, and thecooling control system should be designed to prevent any water from penetrating the communicationinsulator in case of a leakage in the thyristor valve.

6.4.3 Seismic design

The thyristor valve including housing and communication insulator should be designed to fulfillappropriate seismic standards, e.g., IEEE Std 693-1997.

6.5 Valve testing

The tests described apply to the thyristor valve (or valve sections), the valve structure, and thoseparts of the coolant distribution system and firing and monitoring circuits that are containedwithin the valve structure or connected between the valve structure and earth. Other equipment suchas valve control and protection and valve base electronics can be essential for demonstratingthe correct function of the thyristor valve during the tests, but are not in themselves the subject ofthe tests.

6.5.1 Design tests

Thyristors that fail during design tests may be replaced. However, the test should be repeated. If thecombined total of all thyristor failures during design tests exceeds the thyristor valve redundancy level,the design tests should be classified as a test failure.

6.5.1.1 Dielectric tests

6.5.1.1.1 Dielectric tests between thyristor valve terminals and enclosure

The main purpose of these tests is to verify that the insulation between the thyristor valve terminalsand the enclosure (housing) is adequate. The supplier may open or short electronic components of thethyristor valves during these tests. The tests should include:

— Power frequency test— Lightning impulse test

6.5.1.1.2 Dielectric tests between thyristor valve terminals

The main purpose of these tests is to verify the design of the thyristor valve with respect to itscapability to withstand overvoltages between its terminals. The test is performed with the thyristorvalve blocked, voltage applied to the high-voltage terminal, and the low-voltage terminal grounded.Protective device operation is considered to be an acceptable performance. Test levels need to be




WITHDRAWN selected based on the protection design. The supplier should demonstrate that the open-circuit voltageand the internal impedance of the test circuit are representative for the installation. The tests shouldinclude:

— DC test— Power frequency test— Switching impulse test

6.5.1.2 Operational tests

The purpose of these tests is to verify the thyristor valve design for combined voltage and currentstresses under normal and abnormal repetitive conditions as well as under transient fault conditions.These tests can be performed on a prorated section of the thyristor valve that contains at least twolevels. Tests should be performed to verify proper operation in the following operating modes:

a) Operational bypassb) Capacitor reactance up to the limit for each of the system conditionsc) Blocked state

Additionally, tests should be performed to demonstrate proper operation under all unique systemconditions, including, as applicable:

1) Minimum line current (IMIN)2) Maximum continuous current (IR)3) Maximum 30min over current (IT)4) Maximum 10 s over current (ID)

Additionally, tests should be performed to demonstrate proper operation under all unique system faultconditions, including, as applicable:

— Maximum external line section fault: Protective bypass should be demonstrated in a circuit thatproduces currents equal to or higher than those computed for the worst external systemconditions followed by the specified variable capacitive reactance under the highest nonfault linecurrent. The test should be repeated after the reinsertion time, if so rated.

— Maximum internal line section fault: Protective bypass should be demonstrated in a circuit thatproduces currents equal to or higher than those computed for the worst system conditions,usually representing faults on the TCSC terminals. If applicable, the test should include thetrapped current that can occur if the bypass switch closes with the worst timing. The test shouldbe repeated after the reinsertion time, if so rated.

— Fault with normal TCSC operation: With the highest current, during which the TCSC shallnot go into protective bypass, the valve shall be operated at the maximum capacitive reactancefor the duration of these faults. The test shall be repeated after the reinsertion time, if sorated. The test circuits shall produce currents and voltages as computed for worst systemconditions.

6.5.1.2.1 Periodic firing and extinction test

The main objective of this test is to demonstrate the thyristor valve switching capability at elevatedvoltage and current during periodic turn-on and turn-off operations. This test also verifies the properoperation of the dividing/damping network to provide uniform voltage distribution.

6.5.1.2.2 Temperature rise test

The main purpose of this test is to demonstrate that the temperature rise of the most critical heatproducing components is within design limits, to verify that no components or materials aresubjected to excessive temperatures under different steady-state operating conditions, and to verify




WITHDRAWN that the cooling is adequate. One heat run test based on worst case conditions is sufficient to verify thedesign.

The supplier should propose test conditions that represent the most critical thermal stresses, takinginto account all operational, overload and fault duty conditions, including:

— The magnitude of test values and the duration of the tests are adequate.— The cooling conditions are representative of the minimum cooling conditions (minimum coolant

flow and maximum initial temperatures).— The necessary temperature measurements can be made.

6.5.1.2.3 Fault current test with subsequent blocking

This test typically represents the duty imposed by an external fault with thyristor valve bypassing andinsertion.

6.5.1.2.4 Fault current test without subsequent blocking

This test typically represents the duty imposed by an internal fault with thyristor valve bypassing andno thyristor valve blocking (fault current removed by line circuit breaker opening and/or bypassswitch closing).

6.5.1.2.5 High di/dt and dv/dt performance

These tests can be performed on one thyristor level. Tests should be performed to demonstrate that thethyristor valve and the associated electronics can withstand the highest rate of rise of currentassociated with the application.

6.5.2 Production tests

The objective of the tests is to verify proper manufacture.

6.5.2.1 Visual inspection

The test should include a check that all materials and components are undamaged; check of data ofcomponents; and check of air clearances and creepage distances within the thyristor valve/valveenclosure.

6.5.2.2 Connection check

The test should include a check of all the main current carrying connections; check of the clampingforce of thyristors; and check of the point-to-point wiring.

6.5.2.3 Voltage dividing/damping circuit check

The test should include a check of the parameters of the dividing/damping circuits.

6.5.2.4 Voltage withstand check

The test should include a check that the thyristor levels can withstand the voltage corresponding to themaximum value specified for the thyristor valve.

6.5.2.5 Check of auxiliaries

The test should include a check that all auxiliaries function correctly.

6.5.2.6 Firing check

The test should include a check that the thyristors in each thyristor level turn on correctly in responseto firing signals.




WITHDRAWN 6.5.2.7 Cooling system pressure test

The test should include a check that there are no leaks and a check for adequate fluid flow.

6.5.3 Optional tests

Optional tests are additional tests that can be performed, subject to agreement between purchaser andsupplier. The objectives are the same as for the operational tests specified in 6.5.1.2.

7. Capacitors and reactors

7.1 General

It is recommended that the purchaser refer to the applicable IEC or IEEE standards for TCSCcapacitor and reactor component design, manufacturing, and testing requirements to the extentpossible. General requirements that the purchaser should consider include:

a) Capacitor and reactor components furnished by the supplier should be provided with identicalinterchangeable components, to the extent possible, to simplify maintenance and stocking ofspare parts.

b) Components should be equipped with lifting eyes or have similar provisions for liftingindividual units for ease of transportation, installation, and maintenance.

c) Support insulators used for mounting TCSC capacitor and reactor components should befurnished with sufficient creepage and clearance for reliable operation and maintenance of theequipment. Creepage and clearances should be based on the maximum voltage (includingharmonics) appearing across support insulators or bushings.

d) The current rating of the capacitors and reactors should be based on the sum of the squares ofthe current at the power and harmonic frequencies of the TCSC design.

7.2 Capacitor considerations

Capacitors for the TCSC shall be designed, manufactured, and tested in accordance with applicablerequirements of IEEE Std 824-1994. Consideration to operation in capacitive controlled reactancemodeshould be taken when specifying the rated current and voltage of the capacitor. It should be noted thatthe rated current of a TCSC capacitor normally is higher than the rated through current of the TCSC.The actual capacitor current waveforms related to operation in the capacitive controlled reactancemodeshould be included in the equipment specification to the capacitor manufacturer.

7.3 Reactor considerations

The TCSC thyristor reactors should be designed, manufactured, and tested in accordance withapplicable requirements of IEEE Std C57.16-1996. General requirements that the purchaser shouldconsider include:

a) Air-core reactors are surrounded by a magnetic field created by the winding ampere-turns. Thelocation of the reactor relative to metallic structures should be considered by the supplier withregard to inductive heating effects during normal operation, or coupled forces during short-circuit loading of the reactor. All structural and metal framework should be designed tominimize metallic loops and parallel circuits in which induced currents can be coupled. It shouldbe noted that metallic structures, including the platform ground, might alter the reactor’sinductance and quality factor.




WITHDRAWN b) Acoustic noise in the human audible range of the sound spectrum can be produced as a result of

vibrations in the thyristor reactor due to the presence of harmonic currents. The user, asapplicable, should specify the maximum allowable acoustic noise criteria and levels.

c) Thyristor reactor testing should consider the following (IEEE Std C57.16-1996):

1) Production tests:

— Winding dc resistance— Inductance— Total losses and quality factor— Lightning impulse or turn-to-turn test

2) Design tests:

— Temperature rise— Measurement of variation of inductance and resistance with frequency

3) Other tests:

— Thermal short-time overcurrent test or calculation— Mechanical short-circuit test or calculation— Switching impulse test— Applied potential test— Chopped-wave impulse test— Radio influence voltage (RIV) test— Audible sound test or calculation— Seismic verification test or calculation

8. Control and protection

8.1 Control

The TCSC control systems should be specified to meet specific control objectives for which thecontroller needs to respond. The TCSC control system objectives specified by the purchaser shouldinclude:

a) Required control modesb) Manual mode for site testing and maintenancec) Emergency shut down by operator (local and remote)d) Voltage, current, reactance, and reactive power measurementse) Synchronization for appropriate generation of firing pulses to the thyristor valvesf) Startup and shutdown sequencingg) Monitoringh) Control self-supervisioni) Capacitor bank protection

8.1.1 Control functions

Various hierarchy control levels and strategies are typically required to meet specified performancecontrol functions. Control strategies and settings can vary with ac network configuration and arespecific to the project objectives. The effectiveness of any particular TCSC control function should bevalidated by appropriate studies, simulation, and testing (see Annex B). Typical control functions forTCSC applications include reactance control, current (power) flow control, SSR mitigation, poweroscillation damping control, voltage control, and open-loop control (see 5.5).




WITHDRAWN 8.1.2 Control structure

More than one TCSC controllable subsegment (see Figure 1) can be specified by the purchaser orprovided by the supplier depending on the project objectives. To facilitate coordination betweencontrollable subsegments and to ensure appropriate net reactance (XORDER), the TCSC control systemis typically structured in several levels that can be defined as master control (MC) (high level),subsegment control (low level), valve base electronics (VBE), and thyristor electronics (TE).

8.1.2.1 Master control

Information from the ac power system, higher-level orders from the operator, and TCSC capacitorbank status information for each subsegment are combined into a MC subsystem (see Figure 10). Eachcontrol function at this level contributes to the net reactance order (XORDER) set by the MC. The mainfeatures are

a) Control mode selection: Several options may be available to the operator. The two mostcommon are reactance control and current (power) control with other control functionsavailable selectively.

b) Set point and transmission order: A reference can be set based on the control mode selected. Inthe case of power flow control, the regulator will sense the actual flow and adjust the reactanceto meet the set point.

c) Current and voltage signals: Line current and voltage from all subsegments are measured andsent through a fiber optic interface to the MC. It is recommended that all instrumentation,measurements, and cabling are included in the project scope for the supplier for reasons ofcompatibility with the controls to be supplied.

d) Subsegment coordination: Controllable subsegments shall be coordinated according to theiravailability to meet the appropriate net reactance (XORDER) and to establish priorities formeeting control objectives. When more than one subsegment is specified, the control systemshould permit operation with at least one subsegment in service.

e) Set priority: Based on the availability of each subsegment and status information received, theMC should set priorities for each controllable subsegment. The duty can be spread evenly over allsubsegments. In some cases, the use of short-time capability could also be permitted or limited.

f) Interlocking: Interlocking may be required by the purchaser to prevent certain inadvertentoperations, e.g., simultaneous operation between local and remote operation or breakeroperations.

g) Status information: Status of controllable subsegments received from low-level control should beinterfaced with the remote terminal unit (RTU), supervisory control and data acquisition(SCADA) system, and operator interface subsystem.


Figure 10—Master control



WITHDRAWN 8.1.2.2 Subsegment control

Each controllable subsegment has three basic modes of operations (see 5.1). The basic structure isshown in Figure 11. The TCSC control system should be designed to minimize transients associatedwith transitions between these operating modes. Firing angles for thyristor valves are typicallysynchronized to the transmission line current (IL) and sent to a VBE subsystem, normally via fiberoptic cables.

8.1.3 Operating levels

Control of the TCSC installation should be specified for operation at a local and remote (whenrequired) level. Selection of local or remote operation should be selectable by a hardware switch.

Local operation features are described in 8.1.5. When this mode is active, the controller should not beable to be operated remotely.

Remote operation can have features similar to those of the local mode, but a simplified version wouldbe desirable, since it is intended only for operator personnel having to control the TCSC installationfrom a remote control center.

Direct operation from the control panel should also be possible. At this level, the TCSC system cannotbe operated via the operator interface locally or remotely. This level of operation is normally requiredfor testing in manual mode and could be limited to direct reactance control.

8.1.4 Startup procedure

Startup and shutdown procedures are required to ensure safe insertion of TCSC equipment into thetransmission system. A typical startup procedure consists of the following steps:

a) Report from VBEb) Confirmation of no protection alarmsc) Open external grounding and close external isolating disconnect switches (see Figure 1)d) Report from line current supervision (minimal current, platform power active, etc.)e) Open external bypass disconnect switchf) Selection of control mode (default standby mode or blocking)g) Selection of reference


Figure 11—Subsegment control



WITHDRAWN h) Execute start command that will open the capacitor bank bypass switch for insertion, followed

by control enabled

8.1.5 Operator interface

The purchaser should specify the operator interface required to operate the TCSC controller locally aswell as the interface with SCADA and RTU subsystems. This would include such features as require-ments for a computer-screen mimick, mosaic panel, or additions to an existing substation’s controls.

It is recommended that the operator interface should have the following minimum characteristics:

a) Selection and execution:

1) Emergency shutdown2) Control mode3) Operating mode4) Set point or reference5) Open/close breakers and disconnect switches

To prevent misoperation, it is recommended that the selection and execution process shouldinvolve a two-step operation where confirmation of the selected function shall be received andconfirmed before its execution is allowed.The purchaser should define the type of communication interface for the selection of setpoints,e.g., serial data or 12-bit digital.

b) Display of information:

1) System parameters (control settings and thresholds)2) Set point or transmission order3) Confirmation of selected control mode4) System information (current unbalance ratio, energy, varistor temperature, cooling, etc.)5) Staus of the TCSC (position of switching devices, thyristor conduction, trend after

overload, time to resume normal operation, etc.)

c) Change of system parameters:Change of some settings, thresholds, and system conditions (e.g., varistor temperature) shouldbe made possible through this interface and permitted only by qualified personnel.

d) Reset:The purchaser can choose to have the possibility to reset the control system from the operatorinterface, in addition to a reset button on the control panel.

e) Diagnostics:In addition to supervising permanently the status of the TCSC bank, it should be continuouslyself-monitored. The messages and indications resulting from these diagnoses should identifynecessary maintenance work or repair. In addition to information related to the TCSC controlsystem, it should provide status information related to

1) Equipment redundancies2) Power supplies (ac and dc)3) Transmission line

8.2 Protection

Some TCSC protection and control functions are similar to those required for a fixed series capacitorbank installation (CIGRE Working Group 14.18 [B4]). Protection and control functions that should




WITHDRAWN be considered for a TCSC include the following:

a) Protection of TCSC equipment against overstress from system conditions:

1) Capacitor overload2) Varistor fault energy3) Varistor over temperature4) Bypass gap protections5) Thyristor valve overcurrent6) Thyristor valve overvoltage7) Thyristor junction temperature (calculated)8) Thyristor reactor overload

b) Protection functions associated with TCSC equipment failure:

1) Capacitor unbalance2) Platform fault3) Varistor failure4) Bypass switch failure5) Pole disagreement6) Thyristor redundancy7) Thyristor failure8) Thyristor reactor failure9) Controllable subsegment failure10) Cooling system11) Bypass gap failure12) Protection and control system failure13) Current and voltage sensor failures

c) TCSC control functions:

1) Bypassing2) Insertion (automatic or manual) and reinsertion3) Lockout4) Temporary block insertion5) Operation of disconnect switches6) Low line current

d) Power system protective actions (when specified):

1) Harmonic current protection—this function limits exposure of the power system to possibleinteractions with TCSC generated harmonics (CIGRE Working Group 14.18 [B4]).

2) Power oscillation damping—this function will provide power system damping (see 5.5).3) SSR mitigation—this function avoids power system SSR conditions based on detailed

studies (see 5.5).4) Subharmonic resonance—this function limits exposure of the power system to possible

interactions with the TCSC installation and subharmonic resonance (ferroresonance)(IEEE Catalog Number 98TP126-0 [B14]).

8.3 Monitoring and recording

a) Alarms and indications: The purchaser should specify that sufficient alarms and indications beinstalled locally (see Table 2) on the TCSC control panel, in addition to those provided on theoperator interface, especially if the latter is to be installed at a different location. As a minimum,




WITHDRAWN


Table 2—Summary of alarms and indications to operator interface or SER

IndicationControl action

Subsegment Master

EventAll

phases

Each

phase

All

phases

Each

phase

Bypass

switch

Bypass

thyristor

Subsegment availability I

Total TCSC capacitor bank

Phase unbalance L P

Capacitor

Unbalance threshold 1 L

Unbalance threshold 2 L P

Overload I

Overload exceeded L T T

Unavailable I

Varistors

High current I T

High energy I T

Conduction I

Overload exceeded I T

Cooling in process I

Failure L P

Reinsertion

Enabled I

Automatic I

Manual I

Platform failure L P

Optical fiber 1 (out of service) I

Communication failure I

Communication failure I

Power supply in/out

Platform I

Ground I

Thyristor

Bypass I

Blocking I

Loss of redundancy L P

Interface failure L P

Cooling failure I P

Control system on/off I

Control system failure L

(Continued )



WITHDRAWN

the presence of annunciation alarms should be indicated on the control panel. Typically, theannunciation provides the following information:

1) Control and protection system failure2) Power equipment failure3) Normal power system condition and operation, e.g., overload, bypass, varistor conduction

(The acknowledgment of each alarm should be clearly indicated.)

b) Archiving: Archiving refers to the sequence events recorder (SER) and the recording of analog anddigital signals during disturbance events. The information should be synchronized with a timereference signal available at the substation. For locations where no time reference signal isavailable, a global positioning system (GPS) signal can be used as an alternative. Otherwise, aninternal clock corresponding to the time reference in the TCSC control system shall be provided.The time resolution between two events should be within 1ms. The purchaser should specify theminimum number of signals to be recorded so that total memory size can be defined. Memoryshould be of the static type and nonvolatile. Archiving can also be supplied on the operatorinterface unit. It is important to understand, however, that synchronizing and time accuracycannot always be accomplished depending on the operating system used for the operatorinterface.

8.3.1 Alarms and indications to operator interface or SER

A summary of the recommended alarms and indications to the operator interface or SER is shown inTable 2.

8.3.2 Recording of analog and digital signals

Trigger signals to initiate recording of analog and digital signal should be specified by the purchaserand can include those shown in Table 3.


Table 2—Summary of alarms and indications to operator interface or SER (Continued )

IndicationControl action

Subsegment Master

EventAll

phases

Each

phase

All

phases

Each

phase

Bypass

switch

Bypass

thyristor

Bypass switch

Open/close external I

Open/close internal I

Open/close manual I

Position I

Disagreement L

Failure L

Lockout permanent L

Lockout temporary L

Line trip I

Event initiated I

I¼ Indication when event active.L¼ Indication stays latched until reset.P¼Permanent.T¼Temporary.



WITHDRAWN

8.4 Signal transmission and platform power

Most TCSC installations use fiber optic subsystems to send information from the platform to theground control system. Various methods can be used for data transmission and these include digitalserial data transmission with multiplexing, digital signal transmission, and signal voltage/frequencyconversion and transmission.

Various techniques can be used to provide power to the protection and control equipment on theplatform. These techniques are similar to fixed series capacitor applications and include:

a) Current transformersb) CCVTs (coupled capacitor voltage transformers)c) Batteriesd) Hybrid optical current transformerse) Optical transformers

The technique using optical transformers is independent of line current and voltage, since the power isderived from ground level. This technique is useful when protection and transmission of informationfrom the platform are required at very low line current (� IMIN) and during transmission line powerreversals. However, this should not be a major concern, since failure to equipment is more likely tooccur at higher current levels. Platform power shall respond quickly and return to normal operation inthe event of a system disturbance.

Thyristor valve electronics can derive their power from resistor–capacitor snubber circuits when thethyristor valves are blocked and from current transformers during conduction (see 6.2.2.5). The supplyof thyristor power requires minimum line current (IMIN). The purchaser should evaluate the operatingconsiderations (see 5.5) for TCSC installations during extended periods when there can be powerreversals and the line current approaches zero, and should consider also the fact that thyristor valvesrequire minimum voltage and current for proper firing. Thyristor valve power shall return quicklyafter a system disturbance or abnormal system condition followed by proper response from the control


Table 3—Trigger signals

Analog and digital signals Per subsegment

Capacitor

Total current �Unbalance current �Voltage �

Thyristor current �Varistor total current �TCSC total current �Platform total current �Bypass signal �Line trip signal �Reinsertion request signal �Time signal �



WITHDRAWN system. The TCSC installation requirements and response shall be evaluated carefully for theseconditions.

8.5 General requirements

8.5.1 Objectives

The TCSC protection systems shall be reliable and manufactured under strict quality control usingmaterials, components, and manufacturing methods of the highest quality. The control, protection,and monitoring systems should be designed and manufactured to achieve reliable operation underspecified ambient conditions and with minimum maintenance.

8.5.2 Redundancy

Some installed series capacitors are designed and operated with nonredundant protection and controlsystems. With a redundant protection system, a TCSC installation can remain in service while theother protection system is undergoing maintenance. When two redundant control and protectionsystems are provided, they should be completely independent (from the platform to the ground) inorder to achieve a high level of availability and reliability. As an alternative, to avoid the cost of acompletely redundant system and to increase reliability, the protection system can be designed withtwo separate control and protection systems with separate functions.

8.5.3 Maintenance

All electronic circuits and devices, including those located on the platform, should be easilyaccessible for maintenance. A control system in ‘‘test mode’’ should not affect any redundantsystem.

Providing test apparatus that simulates signals transmitted from the platform can increase availabilityof the TCSC installation. Maintenance work on the ground control panel can be performed entirely onone system if a redundant system is provided.

8.5.4 Safety

The system should be designed so that failure of any part of a subsystem would not cause damageelsewhere in the system nor endanger the safety of personnel (see Clause 10).

8.5.5 Environmental conditions

8.5.5.1 Climatic

Humidity in control panels located on the platform can cause severe damage to the electronic circuitryand generate false alarms, spurious firing, and unwanted bypass operations. It is recommended thatthe level of condensation and humidity inside these panels be controlled.




WITHDRAWN Ambient temperature in the control building should be specified by the purchaser. Power consumptioninside control panels can contribute to overheating of some components. It is recommended to locateexcessive heat producing components in the upper part of the panel, since natural convection isnormally preferred.

8.5.5.2 Immunity to electromagnetic interference

The potential of electromagnetic interference affecting low-power electronic circuitry located on seriescapacitor platforms is very high. The platform can be subjected to induced current flow from current-limiting devices and buswork. Electromagnetic noise induction and radiation during operations ofdisconnecting switches and circuit breakers can disturb low-power electronic circuitry located on theplatform. It can cause interference if current transformers and control equipment are not properlyisolated.

8.5.6 Special considerations on testing

It is essential to verify the design of TCSC control and protection equipment, control strategies,associated speed of response, and proper functionality of software before installation at site. It maynot be possible to verify all design and control settings during commissioning under all specifiedoperating conditions (external faults, internal faults, and SSR conditions).

8.5.6.1 Functional tests

Control strategies with appropriate settings are typically developed during system studies. The objectiveof functional testing is to verify the conceptual design (hardware and software) and to ensure that theresponse of the controller under severe power system constraints meets the specified requirement. Thetest shall be designed to subject the hardware and software to fault duties (see 5.4). It is recommendedthat tests be performed to verify all possible interactions between various function and control levels.

8.5.6.2 Environmental tests

These test may be performed according to the IEC 60068-1-1998, IEC 60068-2-2-1974, andIEC 60068-2-3-1969 to verify performance under the specified range of temperature conditions.

8.5.6.3 Dielectric and electromagnetic immunity tests

The control system should be tested for susceptibility to power line disturbances and electromagneticinterference, in accordance with IEEE Std C37.90.1-2002 or IEC 61000-4-2-2001.

8.6 Coordination with line protection

The application of TCSC installations in transmission lines introduces several challenges whenselecting a reliable power system protection scheme. There are several relaying protection schemes thathave been applied successfully on fixed series compensated transmission lines (IEEE Catalog No.98TP126-0 [B14]) that are also suitable for TCSC applications (CIGRE Working Group 14.18 [B4]).However, details of these schemes are beyond the scope of this recommended practice.

9. Layout

9.1 General

The layout of a TCSC installation should incorporate all operational, safety, and maintenance featuresto provide for reliable operation and ease of maintenance. The equipment and buswork should be




WITHDRAWN arranged to allow for maintenance or replacement of any item, while maintaining personnelsafety without risk of damage to nearby components or equipment. The station equipmentarrangement is normally divided into three distinct areas: substation yard, platform assemblies, andcontrol building.

9.2 Substation yard

The general arrangement of TCSC installation equipment is project dependent. The purchaser shouldspecify the location and interfaces where a TCSC installation is to be installed including the following:

a) Location on the transmission line (substation end or along the line)b) Electrical connections and interface to the power systemc) Location for cabling systems and control buildingd) Area for platform assemblies and cooling systeme) External bypass disconnect, grounding disconnect, and isolating disconnect switch requirementsf) Allowance for future expansion (if applicable)g) Electrical clearances and access for maintenanceh) Storage facilities for spare equipmenti) Station grounding requirements and interface (if applicable)j) Electrical station service interface (ac and dc)k) Seismic design criteria (e.g., IEEE Std 693-1997)

The thyristor valve cooling system can be located in a substation control building, if adequate space isavailable. It is recommended that a separate control building room and containment system be used tominimize exposure to coolant system leaks within the building and between the building and platformassemblies. A separate housing close to the base of the platform assemblies can also be used for thecooling system to reduce exposure to coolant leaks and minimize safety and environmentalcontamination concerns.

9.3 Platform assemblies

The equipment for each phase of a TCSC installation are mounted on elevated platforms insulatedfrom ground and normally enclosed within a fenced area having an entrance gate with key interlocks.The platforms are typically supported by station post type insulators with diagonal bracing (ifapplicable), which should be sized to meet seismic criteria. The platform-mounted equipment is similarto, and may include, fixed series capacitor segments (IEEE Std 824-1994). The thyristor valves,thyristor reactor(s), and cooling system interface can be installed together with, or separate from, theTCSC platform. When a fixed series capacitor is being installed with provisions for future thyristor-controlled capabilities, the purchaser should specify whether there is a preference for a commonplatform for the fixed series capacitor equipment and future thyristor-controlled equipment or aseparate platform for the thyristor valves and thyristor-controlled reactors.

9.4 Control building

A control building or separate housing (container) is required to provide adequate space to install allthe TCSC installation control and protection equipment. Additionally, station service power (ac anddc) as well as heating, ventilation, and air conditioning requirements need to be coordinated betweenthe purchaser and supplier. The supplier typically provides the TCSC installation control, protection,monitoring, and operator interface control panel equipment, while the purchaser provides line relayingand protection, local ac system monitoring, and remote control and monitoring interface equipment.




WITHDRAWN 10. Safety

10.1 Personnel protection

The TCSC installations should follow the personnel protection safety precautions of IEEE Std 824-1994. Additionally, the purchaser should specify any special safety requirements needed for the specificproject application including:

a) The thyristor valve enclosure terminals should be shorted before touching and remain shorteduntil no further handling is necessary. This is to guard against the possibility of an accident,should an open circuit develop within the thyristor valve internal capacitor discharge devices.

b) The thyristor-controlled reactor terminals should be shorted before touching and remain shorteduntil no further handling is necessary. This is to guard against the possibility of an accident,should an open circuit voltage be coupled into the reactor from an external electromagnetic field.

10.2 Discharge devices

The TCSC installations should be provided with discharge devices in accordance with IEEE Std824-1994.

10.3 Grounding provisions

The TCSC installations should be provided with grounding provisions in accordance with IEEEStd 824-1994.

10.4 Handling and disposal

Handling and disposal of TCSC installation capacitor insulating and cooling system fluids shouldfollow the methods such as those prescribed by the United States Environmental Protection Agency orother governing agencies.

11. Testing and commissioning

11.1 Introduction

Testing and commissioning TCSC installations involves a systematic test program that begins with off-site tests on each of the equipment items. Off-site tests involve specified design tests, production tests,and factory control system tests. The test program continues with on-site precommissioning tests ofequipment, station tests, and commissioning tests.

Precommissioning tests involve on-site localized testing and checkout of individual equipment itemsand subsystems. These tests are performed after equipment items are installed at the site to verifyproper installation, adjustment, and local manual operation of an individual piece of equipment orapparatus. Testing of transducers, capacitors, reactors, resistors, disconnect switches, circuit breakers,cooling system, fiber optics, grounding switches, switchgear, motor control centers, thyristor valves,and control and protection panels should be included.

Subsystems consist of equipment items that are grouped together to perform a common function. Thepurpose of subsystem tests is to check independently the necessary functional performance of allTCSC subsystems before starting station testing.




WITHDRAWN The TCSC station testing includes tests to verify that subsystems interact and function according tospecified requirements. These tests involve high-voltage energization of equipment and requirecoordination with system operators.

Commissioning tests includes testing the TCSC installation with transmission system power flows upto the rating of the installation. Various transmission system configurations and power flow levelsshould be configured to test the TCSC installation operational parameters to confirm that specifiedperformance can be achieved. Commissioning tests can involve a period of trial operation followed byacceptance tests and can include staged fault testing.

Testing and commissioning TCSC installations requires planning of test sequences, procedures, andload schedules. Testing and commissioning responsibilities of the purchaser and supplier should bedefined in the specification as well as any on-site testing restrictions due to system operationalconstraints, transmission line outage periods, or other limitations. Areas of responsibility andauthority for operations, safety, reporting, and test documentation should be clearly defined. It isrecommended that an on-site commissioning test plan be developed jointly between the supplier andpurchaser prior to commencing testing. The test plan should include a testing schedule and programindicating the order in which tests should be conducted and test methods to be used for off-site and on-site testing including precommissioning, station tests, and commissioning tests.

Relevant safety requirements and responsibilities for all commissioning tests should be documentedand available on site. The documentation should provide information that identifies precautionsneeded to prevent damage to equipment or any danger to human life. Purchaser safety manuals shouldbe available (see 10.1).

Documentation that should be available and used during the commissioning process includesinventory lists, equipment specifications and drawings, software diagrams, system study results, off-site test results, and manufacturer operation and maintenance manuals.

Documentation of commissioning test results should include a report describing each test seriestogether with all relevant test data (sequence of event recorder printouts, transient fault recorderrecordings, etc.). The report should also include detailed descriptions of unsuccessful tests, outages ormalfunctions, and diagnostic tests leading to any modifications implemented for corrections. Finaldata showing results of any modifications should be documented with appropriate reference to theunsuccessful tests as well as other impacted TCSC documentation changes.

11.2 Design and production tests and factory control system tests

The purchaser should specify the design, production, and control system tests to be performed bythe supplier to verify proper performance of equipment prior to shipment to the site. Design testsare made to verify that the design meets the assigned ratings and will operate satisfactorily underrequired service conditions. Design test requirements are often satisfied by reports of previouslyperformed tests on nearly identical equipment. Production tests are made on each piece ofequipment for quality control, in accordance with industry standards. Design and production testsspecified for the TCSC should incorporate IEEE Std 824-1994 where applicable. Design andproduction tests for the thyristor valve are included in 6.5 of this recommended practice. Controlsystem tests at the factory include functional and standard dynamic performance tests of the TCSCcontrol, and protection hardware and software configured as close as possible to the deliveredconfiguration. The design and production testing of the control equipment for the TCSC can includea demonstration of specific system performance objectives by use of digital computer simulationsand performance verification using a TNA simulator.




WITHDRAWN 11.3 On-site tests

11.3.1 Precommissioning

Precommissioning tests should be performed on site to validate that individual equipment items havebeen properly installed and are functionally operating prior to commissioning tests. Precommissioningtests do not require high-voltage energization, but could require station service power (ac and dc).Precommissioning objectives typically include tests to verify:

a) Equipment is installed in accordance with manufacturers instruction books and station designdrawings

b) Wiring, fiber optics, and grounding connectionsc) Capacitance, reactance, and resistance parametersd) Turns ratio and signal polaritiese) Timing checks on circuit breakers and switchesf) Contact resistance of disconnects and circuit breakersg) AC and dc station service power equipmenth) Cooling systemi) Control, protection, and monitoring equipmentj) Communication interfacek) Remote telecommunications interface and operator interface

11.3.2 Station tests

The TCSC station testing consists of local station tests utilizing many or all of the different subsystemstogether. Station tests are confined to the local station and do not require scheduling of powertransfers on the transmission line except for station service power needs. Switching and initiation oflocal sequences shall be from the local and master operator controls. Testing should begin without acsystem high voltage connected to the TCSC installation with local operational and emergency tripsequences being tested prior to applying ac system high voltage. These tests give system operators anopportunity to become familiar with switching procedures and operator interfaces before actualequipment energization.

When energization tests are performed, the external grounding disconnect switches are opened and theexternal isolating disconnect switches can be closed.

11.3.3 Commissioning tests

a) Transmission testing: Transmission tests include testing all performance requirements undernormal operating conditions and, as conditions permit, under contingency operating conditions.All specified TCSC installation control modes should be tested over the required operatingranges with different levels of power flow. Transmission tests may include:

1) Start, insertion, and bypass sequences2) Steady-state operation at minimum line current3) Block and bypass sequences4) Bypass operation5) Reactance range at rated voltage and current6) Temporary and dynamic overload voltage and current7) Power oscillation damping (when specified)8) SSR mitigation (when specified)




WITHDRAWN b) Trial operation: Trial operation provides an opportunity for sustained operation of the TCSC

installation together with the connected ac system for an extended period of time that shouldstart prior to any warranted operating periods. The purchaser should specify the trial operationperiod (e.g., 10–30 days or longer). This period is a time for accurate observation of thecomplete TCSC installation and all associated components. Trial operation affords thepurchaser a first indication of the TCSC installation’s availability under real operatingconditions.Trial operation should verify that the TCSC installation is capable of reliable operationwith the connected ac system for an extended period of time without misoperation.During trial operation, the TCSC installation should be operated under expected operatingconditions (e.g., operated by trained purchaser operators and dispatchers without supplierassistance).During trial operation, the TCSC installation should demonstrate its capability to perform asspecified during any disturbances in the ac system or communication system for which theTCSC installation is designed or specified. While it is not the intention to stage line faults orac disturbances during trial operation, such events—if they occur during the trial operationperiod—should be used to evaluate the proper performance of the TCSC installation. Alldisturbances during trial operation should be monitored, recorded, and analyzed todetermine the causes and their impact. All alarms should be investigated and properoperation verified.If possible, the TCSC installation and ac network should be operated in various steady-stateconfigurations for extended periods of time. This provides the TCSC installation extendedexposure to different ac system operating conditions prior to acceptance and commercialoperation.

c) Acceptance tests: Acceptance tests should include testing of various performance requirementsincluded in the TCSC installation specifications. Acceptance tests can be performed as aseparate series of tests or integrated into the on-site test program to eliminate test duplicationand reduce overall commissioning time. Acceptance tests verify the overall performance of theTCSC installation and demonstrate that the design is correct and that the as-built installationmeets the requirements of the specifications. Staged system testing provides a cost-effectivemeans to safely evaluate, under controlled conditions, the TCSC installation and power systemperformance during disturbances. As staged fault testing involves the introduction ofdisturbances to the transmission system, the system operator shall typically take responsibilityfor scheduling, structuring, and performing such tests. This holds true for any testing thatinvolves interaction with external equipment or systems, e.g., testing for SSR interaction withassociated generation equipment. In such situations, the supplier should be required to assist instructuring the test plans and have representatives on site to monitor testing procedures. Thetests that are performed should be designed jointly between the system operator and the supplierin order to establish that the associated power system and TCSC installation componentadditions or upgrades meet the minimum specification requirements; can withstand the dutyimposed by disturbances; provide a safe working environment; and do not degrade thetransmission system stability or reliability. Successful completion and documentation ofacceptance tests should result in customer acceptance of the TCSC installation and include thefollowing:

1) Steady-state ratings2) Temporary and dynamic overload tests3) Power oscillation damping performance (when specified)4) SSR mitigation performance (when specified)5) Staged fault tests (when specified)6) Harmonic and interference performance (when specified)7) Audible noise performance (when specified)8) Electrical losses performance report (see Clause 12)9) Cooling system performance




WITHDRAWN 12. Losses and loss evaluation

12.1 Introduction

Purchasers use various accounting methods to evaluate and establish the cost of power losses inelectrical systems (service life, discount rate, capacity costs, load usage, energy costs, transmissioncosts, etc.). These methods are unique to each purchaser as well as to the location of equipmentwithin the power system. It is not within the scope of this recommended practice to provide arecommendation as to what methods should be used to determine the value of electrical losses.However, when evaluating electrical losses for a TCSC installation, the purchaser should establish aset of loss evaluation factors expressed in dollars per kilowatt of losses ($/kW) for each operatingpoint of interest (see Figure 5 and Figure 6). The evaluation factors should take into account thepercentage of time that the TCSC would operate at each point. The economic evaluation of stationlosses should then be arrived at as the sum of the losses at each operating point times the evaluationfactor for that point.

The TCSC installations consist of a number of different pieces of equipment (see Figure 1) with amajority of the electrical losses attributed to the thyristor valves, thyristor valve reactors, and auxiliaryequipment (cooling system and control/protection system). Although it would be desirable todetermine electrical losses by direct measurement of actual losses in an operating TCSC installation, itis widely agreed that making these types of measurements is not practical. This is due to the relativelylow losses of a TCSC compared to the Mvar rating (losses typically less than 0.005%). As a result, it isrecommended that the total losses for a TCSC installation be determined by adding the losses fromeach piece of equipment as derived from individual component tests, calculations, and measurements,as applicable.

12.2 Ambient conditions

12.2.1 General

A set of standard reference ambient conditions for determining power losses in TCSC installations isrecommended in 12.2.2 to 12.2.4. In the event that equipment standards have established a referenceambient condition for loss determination, the applicable method referenced in the equipmentstandards should be used and the losses so obtained corrected to reflect the standard reference ambientconditions indicated.

12.2.2 Outdoor standard reference temperature

It is recommended that an outdoor ambient temperature of 20 �C be used as the standard referencetemperature for determining the total TCSC losses.

12.2.3 Cooling-medium standard reference temperature

Forced air and cooling fluids such as water are used to conduct heat from a piece of equipment andcan influence the temperature rise and associated losses of certain pieces of equipment. Cooling-medium temperatures and flow rates need to be established for a basis when determining the totalTCSC losses. Since cooling-medium parameters are highly design related, it is recommended thattemperatures and flow rates be established between the purchaser and supplier and utilized as a basisfor determining the total TCSC losses.




WITHDRAWN 12.2.4 Standard reference altitude

The reference altitude used for the evaluation of total TCSC power losses should be the actual altitudeof the installation.

12.3 Calculation of losses

12.3.1 General

Electrical power losses of a TCSC installation depend on its operating point. In addition to ac systemline current and TCSC reactance, the TCSC firing angle introduces an additional variable. For ratedconditions of IR and XR, the operating parameters are defined by specific requirements (see Figure 5and Figure 6). However, for line currents (IL) between IMIN and IR, the operating strategy adopted bythe purchaser could have a major impact on total TCSC losses. These strategies could involve thefollowing operational modes:

a) Thyristors blocked: For this operational mode, the thyristor valves receive no gate pulses andthere is zero thyristor valve current. Auxiliary equipment should be assumed connected asrequired for immediate pickup of TCSC operation.

b) Thyristors bypassed: For this operational mode, the thyristor valve gating results in 360� powerfrequency conduction of current through the bidirectional thyristor valve and thyristor reactorswith the auxiliary equipment operating.

c) Controlled operation: For this operational mode, the TCSC can be expected to operate atwidely varying line currents and reactance. When evaluating losses, the purchasershould provide a set of operating points (line current and reactance) that is representa-tive of the expected operating conditions. TCSC losses should be determined for these operatingconditions with the auxiliary equipment operating to support the respective operatingpoints.

In summary, TCSC losses at the individual operating points should be weighted with the purchaser’sevaluation factors and added together to obtain the equivalent losses for evaluation purposes.

12.3.2 Series capacitor losses

It is recommended that the TCSC series capacitor (C) losses be evaluated in accordance with IEEEStd 824-1994. In general, purchasers do not normally make an economic evaluation of the losses ofthe series capacitor bank during the procurement process. This is because the losses of a seriescapacitor bank that includes capacitor units with an all-film dielectric are very low when comparedto other power equipment. Most fixed series capacitor banks do not have any additionalsignificant components of losses other than capacitor units and fuses. Usually, the discharge currentlimiting reactor (see Figure 1) is in series with the bypass switch, which is normally open. Inthis operating mode, the discharge current limiting reactor contributes no additional losses to thebank. However, in some installations, this circuit is in series with the capacitors. For this case, or ifthe bank is normally bypassed, the losses of the discharge current limiting reactor should beconsidered.

12.3.3 Thyristor valves

It is recommended that the TCSC thyristor valve losses be determined as discussed in 6.1.1.1.




WITHDRAWN 12.3.4 Thyristor reactor losses

The power frequency and harmonic currents in the thyristor reactors should be calculated. Theimpedance of the reactor at the power frequency and the quality factors at the power and harmonicfrequencies should be measured at the factory. The thyristor reactor losses should then be determinedby Equation (11):

PL¼Xn¼49

n¼1

ðILnÞ2XLn

Qn

ð11Þ

where

n is the harmonic number,ILn is the calculated current through the thyristor reactor at nth harmonic, (in amperes),XLn is the thyristor reactor reactance at nth harmonic, XLn ¼ nXL1, (in ohms),Q

nis the thyristor reactor quality factor measured at the nth harmonic,

PL is the thyristor reactor loss.

12.3.5 Auxiliary power system

The TCSC equipment, which is part of the substation auxiliary power system, would include thethyristor valve cooling system and TCSC control and protection system. The electrical power requiredto operate these systems should be included in the TCSC loss evaluation. Since the cooling systempower requirements will vary as a function of the TCSC operating conditions, the purchaser shouldspecify the operating conditions for which the TCSC auxiliary power measurements are to beevaluated. These measurements may be made directly during commissioning tests.

13. Reliability, availability, and maintainability

13.1 Introduction

The purchaser should carefully consider reliability, availability, and maintainability (RAM)requirements of a TCSC installation when preparing a specification. Issues that the purchaser shouldconsider include:

a) Clearly defined RAM terms, definitions, and warranty provisions.b) TCSC installation RAM performance criteria that can be supported by purchaser operational

and economic justifications.c) TCSC installation and surrounding ac system operational profile guidelines over the expected

RAM performance-monitoring period.d) RAM measurement and performance monitoring program.

13.2 Definitions

The following can be used to form the basis for RAM terms and definitions:

a) Forced outages are outages caused by faults in the TCSC installation that result in loss of partor all of the essential functions of the TCSC.

b) Scheduled outages are outages necessary for preventive maintenance to assure continued andreliable operation of the TCSC. They could result in the temporary loss of part or all of theTCSC installation.




WITHDRAWN c) Outage duration is the elapsed time (in hours) from the instant the TCSC installation is out of

service to the instant it is ready to be returned to service. The following should be included inoutage duration:

1) The downtime required to determine the cause of an outage and to determine whichequipment or units of equipment need to be repaired or replaced.

2) The time required by system operators to disconnect and ground equipment in preparationfor repair work and to remove grounds and reconnect equipment after repairs arecomplete. Delays caused by unavailability of qualified purchaser personnel should not beaccumulated in the outage duration.

3) If partial operation of the TCSC is available, the duration of the equivalent outage shouldbe calculated as the product of the derated condition duration (in hours) and the percentageof rated Mvar (3� IR

2�XR) that cannot be achieved during this period.

d) Annual availability is the annual equivalent availability for forced outages, both total andpartial, in percent and is defined by Equation (12) (with duration of equivalent events inhours) as

A ¼ 1�XDuration of equivalent event

8760

� �� 100 ð12Þ

e) Maintainability is the staff hours required to maintain the TCSC installation over a specifiedperiod. Maintainability includes both time required to correct a forced outage and the timerequired to perform scheduled or preventative maintenance.

13.3 RAM analysis

During design of the TCSC installation, it is recommended that the supplier performs studies thatshow the proposed design can meet the RAM performance requirements.

13.4 Spare parts

The basic supply of the TCSC should include a full complement of essential spare parts, which are tobe furnished at the same time and as a part of the TCSC supply. It is the purchaser’s responsibility,based on suppliers’ recommendations, to provide adequate spare parts to meet the RAMrequirements.

The spare parts strategy should be based on a tabulation of all of the components in the TCSC, downto the level of the lowest ‘‘replaceable module.’’ Each component in the tabulation can be identified forits importance to the operation of the TCSC, according to the following classification:

— Category A: TCSC operation is not possible until this component has been repaired or replaced.— Category B: TCSC operation can continue (or resume) at reduced rating, but further failures

could lead to a TCSC outage.— Category C: TCSC operation can continue on an emergency basis, but a critical function has

been lost or bypassed. Some risk of further complications or equipment damage exists until thefunction is restored.

— Category D: TCSC operation can continue without serious impairment.

It is recommended that the tabulation include the failure rate or the expected replacement rate of thecomponent over a 5-year period. The tabulation should include the manufacturer’s name and modelnumber, suggested source, and estimated delivery cycle.




WITHDRAWN The number of spares for the Category A items should include a confidence factor of 90% probabilitythat a part is available in the event of a failure. If the purchaser cannot sustain long-term outages,the confidence factor becomes 100% and all Category A items have at least one spare unit availableon site.

The spare parts for the TCSC should be stored on site, and the TCSC installation should be designedto include suitable storage facilities. Where appropriate, storage arrangements for indoor and outdoorequipment should be seismically qualified.

13.5 Availability and reliability

When TCSC RAM requirements are needed, it is recommended that RAM performance factorsinclude the following:

a) The purchaser should specify the required annual availability for forced outages of the TCSC(in percentage).

b) The purchaser should specify the required maximum number of forced outages of the TCSC(per year).

c) The supplier should state the expected or guaranteed average number and duration of scheduledoutages per year.

d) The supplier should guarantee the quoted availability performance (in years) following the startof commercial operation. The purchaser should notify the supplier of outages. During theguarantee period, the purchaser should maintain records of the number and duration of forcedand scheduled outages, hours of operation, and other relevant data and should make thoserecords available to the supplier upon request. If the actual performance is below the guaranteevalues, the supplier should provide corrections and modifications to the RAM guarantees at noextra cost to the purchaser. The RAM guarantees should then be extended until the specifiednumber of continuous years of RAM performance has been achieved.

e) Maintenance intervals should occur regularly for inspection and, where necessary, repair. Thesupplier should suggest the maintenance interval suitable for its equipment and should describeany condition monitoring provided.

14. Project scope

14.1 Introduction

The purchaser should clearly define the scope of supply for the overall TCSC project. The scopedefinition should include all material and services that the supplier shall provide in order to completethe project, either in combination with work by the purchaser or others, or as a total turnkey project(see IEEE Std 1267-1999). The purchaser may request a separate proposal for the construction andinstallation portion of the project as an option for comparison purposes. Whatever scope or scopeoption is specified, a required project completion date should be specified by the purchaser. Theproject scope will vary slightly depending on whether the TCSC installation being specified is a newinstallation, or a retrofit to an existing fixed series capacitor installation.

14.2 New TCSC installations

a) Application studies: The purchaser should define the design documentation that shall becompleted by the supplier (see 16.3). Annex B discusses the studies that should be completed in




WITHDRAWN order to apply correctly a TCSC installation to the system. Any system data or results fromprevious study work by the purchaser that are currently applicable should be indicated and maybe included in the specification (as appropriate).

b) System design:

1) Design—Generally it is to the purchaser’s advantage to allow the supplier to design theoverall TCSC installation based on the specification requirements and the suppliers’ specificcapabilities, experience, and practices. As a minimum, the purchaser should specify thedesired TCSC system performance requirements.

2) Yard layout—When a TCSC installation is to be installed in an existing substation, thepurchaser should provide yard layout drawings showing available space for the TCSCequipment including overhead limitations and utilities. It is recommended that a site walk-through be required with the purchaser and supplier. When the TCSC installation is to belocated in a new substation, the purchaser should define maximum dimensional areas forthe TCSC equipment or otherwise define limitations on available space. The suppliershould be required to provide an equipment layout drawing showing the arrangement ofTCSC equipment into the physical area allotted.

3) Control building—The purchaser should indicate whether the enclosure for ground levelcontrols will be the responsibility of the supplier, the purchaser, or others. The suppliershould be required to provide an outline drawing of ground level control equipment anddefine the space, cooling, and station service power requirements (ac and dc) for the controlequipment.

c) Supply of equipment: The scope of equipment supply should be clearly defined by the purchaser.Generally, it is to the purchaser’s advantage to require the supplier to design and providethe entire system including all platform-mounted equipment, controls, communication withground level controls, thyristor cooling equipment, and, in most cases, bypass switchand external bypass disconnect switch (see Figure 1). The purchaser should indicatewhether external grounding and isolating disconnect switches are to be included in thesuppliers’ scope.

d) Installation:

1) Turnkey—Typically, a turnkey installation is applicable only where the specified location isa new substation. Here, the purchaser should define the area limitations and location ofexisting and future overhead lines, utilities, roads, etc. The purchaser should indicate whowill provide required permits and geotechnical studies. It should be clearly stated what thesupplier is required to provide, e.g., the site preparation, grounding system, foundations,fence, platform, required yard structures, bus work and switches, control building, andTCSC equipment installed, tested, and commissioned.

2) Limited turnkey—Where the purchaser elects to perform some or all site work, or it isto be provided by others or, in the case of an existing substation, site requirementsare already met, the purchaser should clearly define the degree of installation requiredby the supplier. This can range from supervision of installation of equipment by othersto full installation of equipment including foundations, control house, and disconnectswitches.

e) Testing and commissioning: The purchaser should define the testing and commissioningrequirements of the supplier (see Clause 11).

f) Training and documentation: The purchaser should define the required operator training,training and operating manuals, and instruction books (see Clauses 15 and 16).

g) Maintenance: The purchaser should require the supplier to provide a recommendedmaintenance schedule as well as reliability data for the purposes of proposal evaluation and




WITHDRAWN contract warranty provisions (when desired). The maintenance schedule should be presented indetail during the maintenance training with detailed instructions for each piece of equipmentrequiring maintenance. The purchaser may wish to include as part of the project scope amaintenance program provided by the supplier.

14.3 Retrofit to an existing fixed series capacitor installation

Differences between the project scope elements of a new (see 14.2) versus retrofitted to an existing fixedseries capacitor installation are listed as follows:

a) Application studies: No modifications.

b) System design:

1) Design—No modifications2) Yard layout—The purchaser should provide equipment outline drawings of the existing

fixed series capacitor bank as well as yard layout drawings showing available space for theTCSC installation including overhead limitations and utilities. It is generally recommendedthat a site walk-through be required with the purchaser and supplier. The supplier shouldbe required to provide an equipment layout drawing showing the arrangement of TCSCequipment relative to the existing equipment.

3) Control building—The purchaser should provide details of existing ground level controlbuildings. It should indicate whether additional enclosures for ground level controls, ifrequired, shall be the responsibility of the supplier, the purchaser, or others. The suppliershould be required to provide an outline of ground level control equipment and definethe space, cooling, and station service power (ac and dc) requirements for the controlequipment.

c) Supply of equipment: The scope of equipment supply should be clearly defined by the purchaser.Generally, it is to the purchaser’s advantage to require the supplier to design and provide theentire system including all platform mounted equipment, controls, communication with groundlevel controls, thyristor cooling equipment, and bypass switch.

d) Installation:

1) Full turnkey—Typically will not apply in this case.2) Limited turnkey—The purchaser should clearly define the degree of installation required.

Because the thyristor-controlled portion shall be carefully integrated into existing fixedseries capacitor equipment, it is recommended that the supplier be given responsibility forthe complete installation of the TCSC equipment. The purchaser should specify whether ornot the supplier will be responsible for installation of foundations, control building, anddisconnect switches.

e) Testing and commissioning: The purchaser should define the testing and commissioningrequirements of the supplier (see Clause 11).

f) Training and documentation: The purchaser should define the required operator training,training and operating manuals, and instruction books (see Clauses 15 and 16).

g) Maintenance: The purchaser should require the supplier to provide a recommendedmaintenance schedule as well as reliability data for the purposes of proposal evaluation andcontract warranty provisions (when specified). This maintenance schedule should be presentedin detail during the maintenance training with detailed instructions for each piece of equipmentrequiring maintenance. The purchaser may wish to include as part of the project scope amaintenance program provided by the supplier.




WITHDRAWN 15. Training

15.1 General

The purchaser should specify the training needs for a TCSC installation. It is recommended that thetraining program include operator/dispatch and maintenance training for the engineering, operating,and maintenance personnel. The training program should include basic theory, control, protection,operation, and maintenance of the TCSC. Particular emphasis should be placed on the thyristor valvesand their associated control and protection equipment. The training program should include classroominstruction as well as on-site demonstrations and hands-on training with the actual equipment to theextent possible. The purchaser may also specify that the supplier conduct training of operatorpersonnel in conjunction with factory testing of the control and protection system.

The supplier should provide a training outline, sample training manuals, and instructor qualificationsprior to the start of the training. Training manuals can consist of specific sections of the TCSCinstruction books and a copy should be provided to each attendee.

15.2 Off-site training

Off-site training is training occurring at the supplier facilities, purchaser control center, or thepurchaser central training facilities. This training includes theory of operation, generic control, andprotection software maintenance, and generic control, and protection hardware maintenance.Training can be combined with witness testing of the control system.

15.2.1 Classroom instruction

The purchaser should specify a classroom training location that is convenient for purchaser’spersonnel to attend. It is generally advantageous to conduct classroom training in close proximity tothe equipment installation in order to facilitate a transition to on-site training. Individual classroomsessions can be specified according to particular work functions, or all work functions can beaddressed in one session in order to provide comprehensive instruction to all personnel.

Operator/dispatch training should be structured to familiarize operating personnel with theoperational features of the TCSC installation, so that at the completion of the training they shallunderstand the operating control modes and characteristics of the TCSC installation. The trainingsession should include basic theory, functional control modes, protective features, and a review of thesystem application studies. The purchaser should consider including Independent System Operatorand Regional Transmission Organization (RTO) personnel in this training.

Maintenance training should be limited to new or more completed components of the TCSCsuch at the thyristor valve, control and protection system, and the water-cooling system. Purchasermaintenance personnel should be present during the control and protection factory system tests.

15.2.2 Factory training

The purchaser may specify hands-on training of operator personnel to take place concurrent withfactory testing of the control and protection system at the supplier’s facility. This training programwould serve the dual purpose of allowing the purchaser’s personnel to witness and verify the testing of




WITHDRAWN the system while providing hands-on training with the actual system being supplied. This trainingshould be structured to follow the factory test plan, while familiarizing purchaser operating personnelwith the operational features of the TCSC control and protection system. The training session shouldinclude functional control modes, protective features, system diagnostics, and control software settingselection and software troubleshooting. The purchaser should indicate the number of personnelexpected to attend the factory testing training program.

15.3 On-site training

It is recommended that training be provided for purchaser operation and maintenance personnel at thesubstation site during precommissioning of the TCSC. Purchaser technical and maintenance personnelshould take part in the installation and testing work in cooperation with the supplier’s personnel. Thesupplier should, however, be responsible for the work. At the completion of the training, thepurchaser’s maintenance personnel should be able to operate, perform preventative maintenance,perform diagnostics, replace defective components, and assist in remote troubleshooting procedures.Larger and well-staffed purchasers could require training to maintain completely and properly theTCSC installation equipment without supplier assistance. The on-site training session should include:

a) Basic theory and explanation of the TCSC installation equipment, including design principles,functional operation, overvoltage protection, thyristor valves, cooling system, fiber opticsubsystems, protective devices, varistors, and control and protection equipment.

b) Demonstration and explanation of recommended tests, diagnostics, and repair proceduresrequired to install, operate, and maintain the station equipment and controls.

c) Maintenance requirements—All TCSC equipment maintenance manuals, equipment drawings,and off-site test reports should be available to each trainee attending the on-site training course.

d) Instructions for ordering replacement parts and telephone numbers for technical assistance.

15.4 Training during commissioning

It is recommended that purchaser operating and maintenance personnel be given instruction andtraining on the actual equipment being furnished during commissioning of the TCSC installation. Theobjectives of this training should be to familiarize purchaser personnel with the operation of stationequipment prior to final acceptance and commercial operation.

16. Documentation

16.1 Introduction

Documentation furnished by the purchaser should be listed and provided in the specification.Documentation to be provided by the supplier should be specified.

16.2 Purchaser documentation

Technical documentation typically furnished by the purchaser in the specification includes:

a) Location mapb) Switching diagramc) Single line diagramd) General plot plan




WITHDRAWN e) Transmission line approach plan and profilef) Key grounding plang) Duct bank plan and profileh) Cable trench plani) Station service diagramj) Geological datak) Ground resistivity datal) Building drawingsm) AC system and transmission line datan) Control panel outline/footprint drawings (as applicable)o) Environmental issuesp) Existing protection single line diagram

16.3 Supplier documentation

Requirements for technical documentation to be provided by the supplier should be specified by thepurchaser. The supplier furnished documentation is typically used for construction, design verification,operation, training, commissioning, and maintenance of the TCSC installation over its expectedoperating life and can include:

a) Document tree: A dynamic index listing project documents including study reports, drawings,inventory list, test plans, test reports, instruction books, and training manuals. The documenttree is typically developed during the life of the contract and updated on a timely basis. Status ofrequired documents is indicated such as latest revision, initial submittal, under review, approvedfor construction, final acceptance, etc.

b) Master testing and commission plan: An overall project test schedule and program indicating theorder in which tests shall be conducted and test methods used.

c) Inventory list or list of deliverables: A complete list of contract materials, spare parts, testequipment, hardware, and software furnished by the supplier.

d) Drawings: The purchaser should specify any specific format requirements for drawingsubmittals and design calculations. The drawings and data can include:

1) Revisions to existing drawings2) Civil and mechanical drawings3) Electrical drawings4) Equipment drawings5) Control and protection drawings

e) System information manual: A general description of the TCSC installation, including overallconfiguration, intended use, major characteristics, and limitations.

f) Training manuals: Manuals used for operator and maintenance training (hardware andsoftware) may consist of specific excerpts from the TCSC instruction books.

g) Software documents: Software information for each computer program including:

1) Purpose2) Usage3) Flowchart, block diagrams, logic diagram, etc.4) Test procedure5) Maintenance instructions including procedures for revising software

h) Operations manuals: A document with detailed procedural instructions required to operate theTCSC installation equipment.

i) Instruction books: Instructions and information for installation, preventative maintenance,troubleshooting, repair, and parts replacement for the TCSC installation equipment.




WITHDRAWN j) Test reports: Off-site and on-site documentation (see Clause 11)k) Studies and design documentation: Studies, technical descriptions, specifications, calculations,

and supplementary data that document compliance with the TCSC installation specification.This documentation can include the following:

1) Insulation coordination study2) Transient overvoltage study3) Harmonic current and voltage levels study4) Temporary and dynamic overload ratings study5) Varistor rating study6) Power oscillation damping study7) SSR mitigation characteristics study8) Operating control modes9) Electrical and audible noise specifications and tests10) Reliability and availability study and performance record11) Demonstration of the TCSC installation control and protection performance including

fault duty cycle ratings factory test requirement12) Station service requirements (ac and dc) design report13) Grounding system requirements specification14) Lightning protection specification15) Losses and loss evaluation study

l) As-built drawings and data.




WITHDRAWN Annex A

(informative)

Bibliography and annotated bibliography

A.1 Bibliography

[B1] Agrawal, B.L. and Hedin, R.A., ‘‘Advanced series compensation (ASC): steady state, transientstability and subsynchronous resonance study,’’ Flexible AC Transmission System (FACTS) EPRIConference, Boston, MA, May 18–20, 1992.

[B2] Angquist, L., Ingestrom, G., and Jonsson, H.A., ‘‘Dynamical performance of TCSC schemes,’’paper 14-302, 1996 CIGRE session.

[B3] Christl, N., Hedin, R., Krause, P.E., Luetzelberger, P., Pereira, M., Sadek, K., and TorgersonD.R., ‘‘Advanced series compensation (ASC) with thyristor controlled impedance,’’ 1992 CIGRESession, SC-14/37/38-5.

[B4] CIGRE Working Group 14.18, ‘‘Thyristor controlled series compensation,’’ CIGRE TechnicalBrochure 123, Dec. 1997.

[B5] Cope, L., Hedin, R., Mah, D., and Weiss, S., ‘‘Thyristor controlled series compensation to avoidSSR,’’ FACTS Conference 3, Baltimore, MD, EPRI TR-107955, Oct. 1994.

[B6] Dolan, P.S., Smith, J.R., and Mittelstadt, W.A., ‘‘A study of TCSC optimal damping controlparameters for different operating conditions,’’ IEEE Transactions on Power Systems, vol. 10, no. 4,p. 1972, Nov. 1995.

[B7] Gama, C.A., Scavassa, J.L., Da Silva, W.M., Da Silva, J.M.M., and Ponte, J.R., ‘‘Prospectiveapplication of advanced series compensation to improve transmission system performance,’’ paper14-204, 1994 CIGRE Session.

[B8] Gama, C., Salomao, J.C.S., Gribel, J.B., and Ping W., ‘‘Brazilian North–South interconnection—Application of thyristor controlled series compensation (TCSC) to damp inter-area oscillation mode,’’The Future of Power Delivery in the 21st Century, San Diego, CA, EPRI TR-109806, Nov. 1997.

[B9] Gama, C., Gribel, J., Ping, W., and Cavalcanti, J., ‘‘Brazilian North–South Interconnection—Application of thyristor controlled series compensation (TCSC) to damp inter-area oscillation mode,’’paper 14–201, 1998 CIGRE Session.

[B10] Hedin, R.A., Weiss, S., Torgerson, D., and Eilts, L.E., ‘‘SSR characteristics of alternativetypes of series compensation schemes,’’ IEEE Transactions on Power Systems, vol. 10, no. 2, p. 845,May 1995.

[B11] Helbing, S.G. and Karady, G.G., ‘‘Investigations of an advanced form of series compensation,’’IEEE Transactions on Power Delivery, vol. 9, no. 2, Apr. 1994.

[B12] Holmberg, D., Danielsson, M., Halvarsson, P., and Angquist, L., ‘‘The STODE thyristorcontrolled series capacitor,’’ paper 14-105, 1998 CIGRE session.




WITHDRAWN [B13] IEEE 100, The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition.

[B14] IEEE Catalog Number 98TP126-0, Fixed Series Capacitor Bank Protection.

[B15] IEEE FACTS Working Group, ‘‘FACTS applications,’’ IEEE 96TP116-0, IEEE PowerEngineering Society, 1996.

[B16] Jalali, S.G., Hedin, R.A., Pereira, M., and Sadek, K., ‘‘A stability model for the advanced seriescompensation,’’ IEEE Transactions on Power Delivery, vol. 11, no. 2, Apr. 1996.

[B17] Larsen, E., Bowler, C., Damsky, B., and Nilsson, S., ‘‘Benefits of thyristor controlled seriescompensation,’’ paper 14/37/38-04, 1992 CIGRE Session.

[B18] Larsen, E.V., Clark, K., Miske, S.A., and Urbanek, J., ‘‘Characteristics and rating con-siderations of thyristor controlled series compensation,’’ IEEE Transactions on Power Delivery, vol. 9,no. 2, p. 992, Apr. 1994.

[B19] Othman, H.A. and Angquist, L., ‘‘Analytical modeling of thyristor-controlled series capacitorsfor SSR studies,’’ IEEE Transactions on Power Systems, vol. 11, no. 1, Feb. 1996.

[B20] Paserba, J., Miller, N.W., Larsen, E.V., and Piwko, R.J., ‘‘A thyristor controlled seriescompensation model for power system stability analysis,’’ IEEE Transactions on Power Delivery,vol. 10, no. 3, pp. 1471–1476, Jul. 1995.

[B21] Perkins, B.K. and Iravani, M.R., ‘‘Dynamic modeling of a TCSC with application to SSRanalysis,’’ IEEE Transactions on Power Systems, vol. 12, no. 4, p. 1619, Nov. 1997.

[B22] Pilotto, L.A.S., Carvalho, A.R., Long, W.F., Alvarado, F.L., and Edris, A., ‘‘The impact ofdifferent TCSC control methodologies on the subsynchronous resonance problem,’’ The Future ofPower Delivery 1996 Conference, Washington, DC, EPRI TR-107089, Dec. 1996.

[B23] Piwko, R.J., Bowler, C., Donnelly, M.K., Trudnowski, D.J., Eden, J.D., Hauer, J.F., Erickson,D.C., and Wilkinson, T., ‘‘Test results and initial operating experience for the BPA 500 kV thyristorcontrolled series capacitor unit at Slatt substation,’’ FACTS Conference 3, Baltimore, MD, EPRITR-107955, Oct. 1994.

[B24] Taranto, G.N. and Chow, J.H., ‘‘A robust frequency domain optimization technique for tuningseries compensation damping controllers,’’ IEEE Transactions on Power Systems, vol. 10, no. 3,Aug. 1995.

[B25] Tenorio, A.R.M., ‘‘A thyristor controlled series capacitor model for electromagnetic transientstudies,’’ M.Sc. thesis, University of Manchester Institute of Science and Technology—UMIST,Manchester, UK, 1995.

[B26] Tenorio, A.R.M. and Gama, C., ‘‘Improvements for power systems performance: modeling,analysis and benefits of TCSCs,’’ Proceedings of IEEE Winter Meeting, Singapore, 2000.

[B27] Trudnowski, D.J., Donnelly, M.K., and Hauer, J.F., ‘‘Estimating damping effectiveness ofBPA’s thyristor controlled series capacitor by applying time and frequency domain methods tomeasured response,’’ IEEE Transactions On Power Systems, vol. 11, no. 2, p. 761, May 1996.

[B28] Venkatasubramanian, V. and Taylor, C.W., ‘‘Improving Pacific intertie stability using Slattthyristor controlled series compensation,’’ IEEE Power Engineering Society Winter Meeting 2000,Singapore, vol. 2, pp. 1468–1470.




WITHDRAWN [B29] Zhou, X. and Liang, J., ‘‘Overview of control schemes for TCSC to enhance the stabilityof power systems,’’ IEEE Proceedings: Generation, Transmission, and Distribution, vol. 146, no. 2,pp. 125–130, Mar. 1999.

[B30] Zhu, W., Spee, R. Mohler, R.R., Alexander, G.C., Mittelstadt, W.A., and Maratukulam, D.,‘‘An EMTP study of SSR mitigation using the TCSC,’’ IEEE Transactions on Power Delivery, vol. 10,no. 3, p. 1479, Jul. 1995.

A.2 Annotated bibliography

Select readings from various publications covering TCSC subjects that include control, generaldescription, modeling, planning, specific projects, reliability, and design/performance are furnished forthe benefit of readers who may wish additional information.

A.2.1 Control

[B31] Clark, K., Fardanesh, B., and Adapa, R., ‘‘Thyristor controlled series compensation applicationstudy—control interaction considerations,’’ IEEE Transactions on Power Delivery, vol. 10, no. 2,pp. 1031–1037, Apr. 1995.

[B32] Fahrioglu, M. and Alvarado, F.L., ‘‘Using TCSC devices for optimal economic dispatch,’’ 1994North American Power Symposium, Kansas State University, Manhattan, KS, vol. 2, pp. 543–547,Sept. 26–27, 1994.

[B33] Gustafson, E., Aberg, A., and Astrom, K. J., ‘‘Subsynchronous resonance a controller for activedamping,’’ 1995 IEEE Conference on Control Applications, Albany, NY, pp. 389–394, Sept. 28–29,1995.

[B34] Liu, C. and Pahalawaththa, N.C., ‘‘A novel algorithm for fast control of TCSC transients,’’International Power Engineering Conference, Nanyang Technological University, Singapore, vol. 1,pp. 241–246, 1999.

[B35] Padiyar, K.R. and Uma Rao, K., ‘‘Discrete control of TCSC for stability improvementin power systems,’’ 1995 IEEE Conference on Control Applications, Albany, NY, pp. 246–251,Sept. 28–29, 1995.

[B36] Wang, L., Girgis, A.A., and Edris, A.A.,‘‘Nonlinear controller design for thyristor controlledseries compensation to enhance power system transient stability,’’ Stockholm Power Tech InternationalSymposium on Electric Power Engineering (IEEE, USA), Stockholm, Sweden, vol. 2, pp. 109–114, Jun.18–22, 1995.

A.2.2 TCSC general description

[B37] Chamia, M., Angquist, L., Noroozian, M., and Andersson, G., ‘‘Controlled seriescompensation—a powerful tool for improved transmission performance,’’ CIGRE 1993. Interna-tional Conference on Large High Voltage Electric Systems, Paris, France, pp. 251–263, Oct. 4–8,1993.

[B38] Christl, N., Hedin, R., Krause, P.E., McKenna, S.M., Sadek, K., Lutzelberger, P., Montoya,A.H., and Torgerson, D., ‘‘Advanced series compensation (ASC) with thyristor controlled




WITHDRAWN impedance,’’ CIGRE Proceedings of the 34th Session, Paris, France, vol. 2, pp. 14/37/38-05/1–11, Aug.30–Sept. 5, 1992.

[B39] Hingorani, N.G. ‘‘Flexible AC transmission,’’ IEEE Spectrum, USA, vol. 30, no. 4, pp. 40–45,Apr. 1993.

[B40] Hingorani, N.G., Hedin, R.A., Stump, K.B., Schwalb, A.L., and Mincer, N., ‘‘New scheme fordamping of subsynchronous resonance in series compensated AC transmission systems,’’ InternationalConference on Thyristor and Variable Static Equipment for ac and dc Transmission, IEE, London, UK,pp. 60–64, Nov. 30, 1981.

[B41] Johnson, R.K., Torgerson, D.R., Renz, K.T., Juette, G., and Weiss, S., ‘‘Thyristor control givesflexibility in series compensated transmission,’’ Power Technology International (United Kingdom),London, UK, pp. 99–103, 1993.

[B42] Johnson, R.K., Torgerson, D.R., Christl, N., Lutzelberger, P., Renz, K., Sadek, K., andWeiss, S., ‘‘Advanced series compensator provides flexibility for AC transmission systems,’’ CIGRE1993. International Conference on Large High Voltage Electric Systems, Gold Coast, Qld., Australia,pp. 242–250, Oct. 4–8, 1993.

[B43] Kosterev, D.N., Kolodziej, W.J., Mohler, R.R., and Mittelstadt, W.A., ‘‘Robust transientstability control using thyristor-controlled series compensation,’’ 1995 IEEE Conference on ControlApplications, Albany, NY, pp. 215–220, Sept. 28–29, 1995.

[B44] Larsen, E., Bowler, C., Damsky, B., and Nilsson, S., ‘‘Benefits of thyristor controlled seriescompensation,’’ CIGRE Proceedings of the 34th Session, Paris, France, vol. 2, pp. 14/37/38-04/1–8,Aug. 30–Sept. 5, 1992.

[B45] Larsen, E.V. ‘‘Thyristor-controlled series compensation—an overview,’’ InternationalColloquium on HVDC and Flexible AC Power Transmission, CIGRE, Wellington, New Zealand,pp. 8.3/1–10, Sept. 29–Oct. 1, 1993.

[B46] Noroozian, M., ‘‘Application of shunt and series compensators for damping of electromecha-nical oscillations,’’ IEE Colloquium (Digest), IEE, Stevenage, UK, no. 278, pp. 4/1–4/3, 1998.

[B47] Unterlass, F., Weiss, S., and Renz, K., ‘‘Control and protection of advanced seriescompensation,’’ Canadian Electrical Association Engineering and Operating Conference, Toronto,Canada, pp. 1–25, Sept. 13–16, 1992.

A.2.3 Modeling

[B48] Gama, C. and Tenorio, R., ‘‘Improvements for power systems performance: modeling, analysis,and benefits of TCSCs,’’ 2000 IEEE Power Engineering Society Winter Meeting, Singapore, vol. 2,pp. 1462–1467, Jan. 23–27, 2000.

[B49] Hammad, A.E. ‘‘Comparing the voltage control capabilities of present and future varcompensating techniques in transmission systems,’’ IEEE Transactions on Power Delivery, vol. 11,no. 1, pp. 475–484, Jan. 1996.

[B50] Jalali, S., Hedin, R., Reitman, T., Torre, W., and Mittelstadt, W., ‘‘Thyristor controlled seriescompensation (TCSC) impedance and linearized models for power swing and torsional analysis. FinalReport,’’ EPRI, Report no. EPRI-TR-110553, May 1998.




WITHDRAWN [B51] McDonald, D.J., Urbanek, J., and Damsky, B.L., ‘‘Modeling and testing of a thyristor forthyristor controlled series compensation (TCSC),’’ IEEE Transactions on Power Delivery, vol. 9, no. 2,pp. 352–359, Apr. 1994.

[B52] Nyati, S., Wegner, C.A., Delmerico, R.W., Piwko, R.J., Baker, D.H., and Edris, A.,‘‘Effectiveness of thyristor controlled series capacitor in enhancing power system dynamics: an analogsimulator study,’’ IEEE Transactions on Power Delivery, vol. 9, no. 2, pp. 1018–1027, Apr. 1994.

[B53] Othman, H.A. and Aengquist, L., ‘‘Analytical modeling of thyristor-controlled seriescapacitors for SSR studies,’’ IEEE Transactions on Power Systems, vol. 11, no. 1, pp. 119–127,Feb. 1996.

[B54] Paserba, J.J., Miller, N.W., Larsen, E.V., and Piwko, R.J., ‘‘A thyristor controlled seriescompensation model for power system stability analysis,’’ IEEE Transactions on Power Delivery,vol. 10, no. 3, pp. 1471–1478, Jul. 1995.

[B55] Perkins, B.K. and Iravani, M.R., ‘‘Dynamic modeling of high power static switching circuits inthe DQ-Frame,’’ IEEE Transactions on Power Systems, vol. 14, no. 2, pp. 678–684, 1999.

[B56] Tenorio, A.R.M., Ekanayake, J.B., and Jenkins, N., ‘‘Modelling of FACTS devices,’’ SixthInternational Conference on AC and DC Power Transmission, IEE, London, UK, Conf. Publ. no. 423,pp. 340–345, 1996.

[B57] Tenorio, A.R.M., Jenkins, N., and Bollen, M.H.J., ‘‘A TCSC model for electromagnetictransient studies,’’ International Symposium on Electric Power Engineering, Stockholm, Sweden, vol. 6,pp. 130–135, Jun. 18–22, 1995.

[B58] Trudnowski, D.J., Donnelly, M.K., and Hauer, J.F., ‘‘Estimating damping effectivenessof BPA’s thyristor controlled series capacitor by applying time and frequency domain methodsto measured response,’’ IEEE Transactions on Power Systems, vol. 11, no. 2, pp. 761–766,May 1996.

A.2.4 Planning

[B59] Canizares, C. A. and Faur, Z. T., ‘‘Analysis of SVC and TCSC controllers in voltage collapse,’’IEEE Transactions on Power Systems, vol. 14, no. 1, pp. 158–165, Feb. 1999.

[B60] Canizares, C.A., Berizzi, A., and Marannino, P., ‘‘Using FACTS controllers to maximizeavailable transfer capability,’’ Bulk Power System Dynamics and Control Symposium, NationalTechnical University, Athens, Greece, pp. 633–642, 1998.

[B61] Dolan, P.S., Smith, J.R., and Mittelstadt, W.A., ‘‘A study of TCSC optimal damping controlparameters for different operating conditions,’’ IEEE Transactions on Power Systems, vol. 10, no. 4,pp. 1972–1978, Nov. 1995.

[B62] Hedin, R., Jalali, S., Weiss, S., Cope, L., Johnson, B., Mah, D., Torgerson, D., and Vossler, B.,‘‘Improving system stability using an advanced series compensation scheme to damp power swings,’’Sixth International Conference on AC and DC Power Transmission, IEE, London, UK, Conf. Publ.no. 423, pp. 311–314, Apr. 1996.

[B63] Kosterev, D.N., Mittelstadt, W.A., Mohler, R.R., and Kolodziej, W.J., ‘‘Application study forsizing and rating controlled and conventional series compensation,’’ IEEE Transactions on PowerDelivery, vol. 11, no. 2, pp. 1105–1111, Apr. 1996.




WITHDRAWN [B64] Larsen, E.V., Clark, K., Miske, S.A. Jr., and Urbanek, J., ‘‘Characteristics and ratingconsiderations of thyristor controlled series compensation,’’ IEEE Transactions on Power Delivery,vol. 9, no. 2, pp. 992–1000, Apr. 1994.

[B65] Luor, T., Hsu, Y., Wang, S., Jeng, L., Guo, T., Lin, J., Chen, Y., and Huang, C., ‘‘Applicationof thyristor-controlled series compensators to enhance oscillatory stability and transmission capabilityof a longitudinal power system,’’ IEEE Transactions on Power Systems, vol. 14, no. 1, pp. 179–185,Feb. 1999.

[B66] Rajaraman, R., Dobson, I., Lasseter, R.H., and Shern, Y., ‘‘Computing the damping ofsubsynchronous oscillations due to a thyristor controlled series capacitor,’’ IEEE Transactions onPower Delivery, vol. 11, no. 2, pp. 1120–1127, Apr. 1996.

A.2.5 Specific projects

[B67] Chen, J., Wang, X., Duan, X., Wang, D., and Zhang, R., ‘‘Application of FACTS devices forthe interconnected line between Fujian network and Huadong network,’’ 2000 Power EngineeringSociety Summer Meeting, Singapore IEEE, USA, vol. 3, pp. 1612–1617, 2000.

[B68] D’Aquila, R., Hill, A.T., Miller, N.W., and Price, W.W., ‘‘Flexible AC transmission system(FACTS) system studies: SouthernCompany Services,’’ EPRI,Report no. EPRI-TR-106461,May 1996.

[B69] Gama, C., ‘‘Brazilian North–South interconnection control—application and operatingexperience with a TCSC,’’ 1999 IEEE Power Engineering Society Summer Meeting, Edmonton, Alta.,Canada, vol. 2, pp. 1103–1108, Jul. 18–22, 1999.

[B70] Gribel, J., Fraga, R., Eiras, M.J., Cavalcanti, J., Tenrio, R., Ping, W., Ricardo, A., Gama, C.,and Leoni, R.L., ‘‘Brazilian North–South interconnection—application of thyristor controlled seriescompensation (TCSC) to damp inter-area oscillation mode,’’ International Conference on Large HighVoltage Electric Systems, CIGRE, Paris, France, vol. 4, pp. 6, Aug. 30–Sept. 5, 1998.

[B71] Hauer, J.F., Mittelstad, W.A., Piwko, R.J. Sr., et al. ‘‘Test results and initial operatingexperience for the BPA 500 kV thyristor controlled series capacitor—modulation, SSR andperformance monitoring,’’ IEEE Technical Applications Conference and Workshops—Northcon/95,Portland, OR, pp. 274–279, Oct. 10–12, 1995.

[B72] Hauer, J.F., Mittelstadt, W.A., Piwko, R.J., Damsky, B.L., and Eden, J.D., ‘‘Modulation andSSR tests performed on the BPA 500 kV thyristor controlled series capacitor unit at Slatt substation,’’IEEE Transactions on Power Systems, vol. 11, no. 2, pp. 801–806, May 1996.

[B73] Kinney, S.J., Mittelstadt, W.A., and Suhrbier, R.W., ‘‘Test results and initial operatingexperience for the BPA 500 kV thyristor controlled series capacitor design, operation, and fault testresults,’’ IEEE Technical Applications Conference and Workshops—Northcon/95, Portland, OR,pp. 268–273, Oct. 10–12, 1995.

[B74] Krause, P., Torgerson, D., Renz, K., Weiss, S., and Lei, X., ‘‘Four years of operationalexperience of the Kayenta advanced Series compensator,’’ International Conference on ElectricalEngineering, International Academic Publishers, Beijing, China, vol. 1, pp. 160–164, 1996.

[B75] Krause, P., Torgerson, D., Renz, K., and Weiss, S., ‘‘Kayenta advanced series compensationoperational experience,’’ Canadian Electrical Association Engineering and Operating Conference,pp. 1–11, Oct. 3–6, 1993; Toronto, Canada, Mar. 20–24, 1994.




WITHDRAWN [B76] Miske, S.A., Lang, R.J., Rowe, S.D., Bilodeau, P., and Granger, M., ‘‘Recent series capacitorapplications in North America,’’ Electricity ‘95, Canadian Electrical Association, Montreal, PQ,Canada, paper 95-EA-114, Vancouver, Canada, Sept. 25–28, 1994, 1995.

[B77] Piwko, R.J., Wegner, C.A., Furumasu, B.C., Damsky, B.L., and Eden, J.D., ‘‘The Slattthyristor-controlled series capacitor project-design, installation, commissioning and system testing,’’35th Session. International Conference on Large High Voltage Electric Systems, CIGRE , Paris, France,vol. 1, pp. 14-104/1–7, Aug. 28–Sept. 4, 1994.

[B78] Piwko, R.J., Wegner, C.A., Kinney, S.J., and Eden, J.D., ‘‘Subsynchronous resonanceperformance tests of the Slatt thyristor-controlled series capacitor,’’ IEEE Transactions on PowerDelivery, vol. 11, no. 2, pp. 1112–1119, Apr. 1996.

[B79] Urbanek, J., Piwko, R.J., Larsen, E.V., Damsky, B.L., Furumasu, B.C., Mittlestadt, W., andEden, J.D., ‘‘Thyristor controlled series compensation prototype installation at the Slatt 500 kVsubstation,’’ IEEE Transactions on Power Delivery, vol. 8, no. 3, pp. 1460–1469, Jul. 1993.

[B80] Venkatasubramanian, V. and Taylor, C.W., ‘‘Improving Pacific intertie stability using Slattthyristor controlled series compensation,’’ 2000 IEEE Power Engineering Society Winter Meeting,Singapore, vol. 2, pp. 1468–1470, Jan. 23–27, 2000.

[B81] Venkatasubramanian, V., Schneider, K.W., and Taylor, C.W., ‘‘Improving Pacific intertiestability using existing static var compensators and thyristor controlled series compensation,’’ BulkPower System Dynamics and Control Symposium, National Technical University, Athens, Greece,pp. 647–650, 1998.

[B82] Zhou, X., Guo, J., Liang, J., Zhang, C., Yin, Y., Hu, X., Chen, Q., Wang, W., Li, B., Chen, Y.,Li, Z., Tao, J., Zhang, Z., and Jiang, J., ‘‘Analysis and control of Yimin–Fengtun 500 kV TCSCSystem,’’ Electric Power Systems Research, Switzerland, vol. 46, no. 3, pp. 157–168, Sept. 1998.

A.2.6 Reliability

[B83] Billinton, R., Fotuhi-Firuzabad, M., and Faried, S.O., ‘‘Power system reliability enhancementusing a thyristor controlled series capacitor,’’ IEEE Transactions on Power Systems, vol. 14, no. 1,pp. 369–374, Feb. 1999.

[B84] Faried, S.O., Billinton, R., and Fotuhi-Firuzabad, M., ‘‘Impact of thyristor controlled seriescapacitor on power system reliability,’’ 1999 PowerTech Conference (IEEE, USA), Budapest,Hungary, pp. 151, Aug. 29–Sept. 2, 1999.

[B85] Fotuhi-Firuzabad, M., Billinton, R., and Omar, S., ‘‘Subtransmission system reliabilityenhancement using a thyristor controlled series capacitor,’’ IEEE Transactions on Power Delivery,vol. 15, no. 1, pp. 443–449, 2000.

A.2.7 TCSC design/performance

[B86] Halvarsson, P. and Angquist, L., ‘‘Controlled series capacitors—practical and economicalsolutions,’’ Electrical Engineering Congress 1994. Part 1 (of 2), National Conference Publication—Institution of Engineers, Crows Nest, NSW, Sydney, Australia, vol. 1, no. 94/11, pp. 147–150,Nov. 24–30, 1994.

[B87] Helbing, S.G. and Karady, G.G. ‘‘Investigations of an advanced form of series compensation,’’IEEE Transactions on Power Delivery, vol. 9, no. 2, pp. 939–947, Apr. 1994.




WITHDRAWN [B88] Noroozian, M., Angquist, L., Ghandhari, M., and Andersson, G., ‘‘Improving power systemdynamics by series-connected FACTS devices,’’ IEEE Transactions on Power Delivery, vol. 12, no. 4,pp. 1635–1640, Oct. 1997.

[B89] Zhu, W., Spee, R., Mohler, R.R., Alexander, G.C., Mittelstadt, W.A., and Maratukulam, D.,‘‘EMTP study of SSR mitigation using the thyristor controlled series capacitor,’’ IEEE Transactionson Power Delivery, vol. 10, no. 3, pp. 1479–1485, 1995.




WITHDRAWN Annex B

(informative)

TCSC application studies and computer models

B.1 Application studies

During planning and design phases of a TCSC project, it is recommended that TCSC configurations bestudied with respect to steady-state, temporary, and dynamic performance (CIGRE Working Group14.18 [B4]; Gama et al. [B7, B9]; Helbing and Karady [B11]; Larsen et al. [B17]). The most commonapplication studies involve power flow, transient stability, small signal, and transient analysis. Electro-magnetic transient program (EMTP) type simulations of transients are typically used for design studies.This annex discusses TCSC equipment model requirements and tools necessary to perform the studies.

In performing system planning studies, an essential first step is to define performance objectives.Operational objectives, as presented in 5.5, should guide the system studies. Careful consideration ofthe specific requirements for the TCSC installation shall provide the basis for a focused equipmentspecification. Possible system performance goals are as follows:

Performance objectives :

Static=quasi-static

Voltage improvement

Precontingency

Postcontingency

Flowcontrol

Pre- and postcontingency

Thermal limits

Contract limits, inadvertent flow

9>>>>>>>>>>>>=>>>>>>>>>>>>;

Power flow analysis

Dynamic

Transient ðfirst swingÞ stabilityDamping

Local modes

Inter area modes

Transient voltage control

Transient overcurrent control

9>>>>>>>=>>>>>>>;

Stability analysis

SSR

Avoidance ðpassiveÞActive mitigation ðsuppressionÞ

�SSR analysis

Once the performance goals are established, analysis typically progresses to power flow and stabilitystudies, in that order. For some applications, small signal analysis and/or transient analysis is alsorequired.

B.1.1 Power flow analysis

Load flow studies can be used to establish steady-state ratings and identify appropriate locations forinstalling a TCSC controller to best meet the study goals and to reduce the alternatives beinginvestigated to focus on the most promising solutions. Additionally, these study results provide initial




WITHDRAWN conditions for transmission system loading and generation used for stability investigations. Simplifiedmodels, which take into account steady-state limits of the network and TCSC controllers, can be usedto evaluate economic tradeoffs to achieve the desired goals associated with the alternatives under study(Gama et al. [B7, B9]).

Initial system planning and feasibility studies for a TCSC can be performed using conventional modelsof series compensation (i.e., negative reactance). As relationships between compensation level(reactance) and system performance are established, attention should then be given to determiningdevice ratings. As the application becomes better defined, consideration of the MVAr and currentratings shown in Figure 6 (see Clause 5) need to be included. The continuous and 30 min ratings wouldbe derived from the power flow analysis. For most feasibility and planning studies, detailed modelingof these limits within the power flow program are not required.

In applications where the functional requirements have been established by this type of analysis, moredetailed simulations incorporating device controller functions could be appropriate.

B.1.2 Power system stability analysis

Stability studies (time and frequency domain) are typically performed during the planning stage toidentify dynamic limiting conditions of the transmission system, and to establish preliminary operatingand reliability criteria needed to achieve improvements in network power transfer capabilities. Theextent to which a TCSC controller can enhance dynamic performance of the network can be revealedfrom investigation of the following:

a) First swing stability (Gama et al. [B7]; Jalali et al. [B16]; Paserba et al. [B20]; Venkatasu-bramanian and Taylor [B28]): A TCSC bank can increase the transient stability margin of thepower system beyond the level typically achieved by a comparably rated fixed series capacitor.With a TCSC, the temporary voltage rating of the series capacitor elements can be utilized toprovide a higher compensation level for immediate post-fault periods. This action furtherreduces the tie-reactance and improves synchronizing torque.

b) Power swing damping: Some power systems often experience undamped low-frequency interareaoscillations (below 1 Hz), when the power transfer between two regions in the system exceeds athreshold. These oscillations are usually initiated by a disturbance in the system. The thresholddepends, among other things, on the strength of the interconnecting transmission systems.TCSC banks offer the possibility of dramatically improved damping of power oscillations andincreased levels of stable power transfer between two regions (Dolan et al. [B6]; Gama et al. [B7,B9]; Taranto and Chow [B24]; Trudnowski et al. [B27]). This is one of the most importantattributes for this device.The TCSC can also yield additional stability benefits by providing a period of maximuminductive compensation during the subsequent return swing. These control objectives can beachieved using a ‘‘band-bang’’ style transient stability control loop, which is active for a shortperiod following the fault.Issues related to the utilization of controlled series compensation in damping power oscillationsinvolve the size of the controlled segment and the choice of controlling signals. While bothissues are system dependent, a small module of the series compensation (e.g., 10%) cansometimes be sufficient for power oscillation damping. Local signals such as line current and busvoltage are effective inputs for detecting oscillations and enabling the TCSC to enhance thedamping of power oscillations.

c) Voltage stability: These studies involve investigating system voltage sensitivity to incrementalincreases in real and reactive power changes to assess voltage collapse phenomena and possiblemitigation by the TCSC. Voltage stability studies require system models that accurately reflectthe load–voltage sensitivity of equipment connected to the network.




WITHDRAWN The TCSC control may be required to meet multiple objectives, including transient stabilization,voltage control, and flow control. Actual implementation of such a control in simulation programs,especially at the conceptual and specification stage, is not normally required. Rather, the studiesshould be aimed at determining the requirements and characteristics of the control needed to meeteach of the system performance objectives, so that these can be included in the equipmentspecification. The equipment supplier shall normally provide the detailed implementation design of thecontroller.

In some applications, an overall compensation scheme shall combine fixed series compensation (FSC)with a TCSC. Coordinated controls can be used to determine which FSC banks should be inserted/bypassed via their bypass switches while the TCSC becomes responsible for providing the fine-tuningand regulation of the desired reactance or current set point.

B.1.3 Subsynchronous resonance (SSR) analysis

Interactions between electrical networks and mechanical shafts of generator–turbine sets have beeninvestigated thoroughly in the literature. Among the instigating factors for SSR interaction, arenetwork-switching events, disturbances, HVDC control interactions, and fixed series capacitivecompensation.

The TCSC controllers have the capability to influence the energy exchange between the seriescapacitor and the turbine–generator shaft. They thus offer the possibility for increasing the permissiblelevel of installed series compensation with very low risk for potential SSR problems. TCSCs are able tomitigate SSR (Hedin et al. [B10]; Holmberg et al. [B12]; Othman and Angquist [B19]; Perkins andIravani [B21]; Tenorio [B25]; Tenorio and Gama [B26]). This allows the application of seriescompensation in locations where it could not be applied in the past.

Two approaches to SSR mitigation using TCSC banks are possible. The first approach is to design anactive controller that monitors SSR oscillations (remote measurements or local estimates) and controlsthe series capacitor voltage to introduce an electrical damping torque. The second and more practicalapproach is to design the triggering control of the TCSC in a manner that makes the TCSC appearresistive–inductive at subsynchronous frequencies and thus eliminates subsynchronous oscillations inthe electrical network, i.e., no torsional interaction between the series capacitor and the shaft of aturbine–generator. The second approach offers more security in the face of varying system conditionsthan the first approach. All approaches have the potential to counteract harmful SSR interactions duenot only to the TCSC itself, but also from nearby fixed series capacitors. Proper implementation of theTCSC firing angle control system is critical for SSR mitigation.

Typically, system planning studies of SSR by the purchaser are limited to consideration of themaximum level of conventional series compensation than can be tolerated. Incremental compensationbeyond that level may then be required to have thyristor control. Detailed evaluation of the SSRbehavior of TCSC is normally beyond the scope of available data/information at the planning stage.SSR evaluation with inadequate modeling of the TCSC can result in erroneous conclusions.Cooperative studies with the supplier, as part of the contract, will normally result in higher fidelityanswers.

B.1.4 Responsibilities

Table B.1 presents a summary of the main studies (study type), which are normally performed duringthe different stages (study category) of a project involving any TCSC application.




WITHDRAWN

B.2 TCSC computer models (Angquist et al. [B2]; Larsen et al. [B18])

The level of detail of TCSC models should be tailored to the objective of the study. For example, if theobjective is the high-frequency electromagnetic transient analysis of a network containing a TCSC, theadopted model has to be detailed, including not only the control system, but also the firing pulsegeneration scheme. On the other hand, if the aim is a power flow or stability analysis, then a verysimple model, like a variable or even fixed reactance at a power frequency, is often sufficient.

From a physical (and ratings) perspective, the TCSC can be split into two basic parts: the high-levelcontrol system and the power equipment, as shown in Figure B.1. The power equipment includes thehigh-voltage equipment such as the capacitors, reactors, and thyristor valves. It also includes the basicfiring controls, which translate reactance orders from the high-level controls into firing pulses for thethyristors. The firing angle of the thyristor valves affects the equivalent reactance of the reactor


Table B.1—Studies

Study type Study categoryResponsible

Purchaser Supplier Joint work

Load flow Planning � �Design � � �

Operational �Stability Planning � �

Design � � �Operational �

SSR Planning � � �Design � � �

Operational �Power system faults Planning �

Design � �Operational �

High-level Control Elements

Power Equipment Elements

FiringControl

MainControl

XORDER

CompensatedTransmission Line

LocalSignal

Ref

SupplementaryControl

RemoteSignals

Figure B.1—TCSC power equipment and high-level control system



WITHDRAWN branch. The high-level control system is responsible for providing the power equipment with areactance order selected to achieve specific operational objectives. The high-level control will providereactance orders intended to maintain specific variables of the system (e.g., impedance level, activepower, or current magnitude through the line) appropriate for steady-state operation, and also forchanging them adequately during transient periods following disturbances on the power system.Division of the TCSC into these two parts is very useful at the design and specification stage of aproject. Performance objectives that affect the power equipment tend to impact the device ratingsdirectly. Implementation of the high-level controls is largely independent of device current, voltage,and reactance ratings, and can be customized to meet the specific requirements of the applications.

For load flow and stability simulation purposes, details of firing controls are unimportant, and simplefundamental frequency impedance models are appropriate.

B.2.1 Modeling for power flow studies (Agrawal and Hedin [B1])

In a power flow program, only the power frequency reactance characteristic of the TCSC device isconsidered. The TCSC can be modeled as a variable series reactance or as a variable series reactance inseries with a fixed capacitive reactance (see Figure B.2). Three different control modes can be adopted inthis case: power (P), current (I), or reactance (X) control. For analysis, the TCSC equivalent reactancein the simulations shall be modified to achieve a desired objective, e.g., active power flow through theline. Implementation of this reactance control can be achieved in two general ways: 1) manual (humanprogram operator) and, 2) automatic (program model). Manual implementation can be very effective,as long as the operator carefully observes the implied control objectives and constraints. This couldrequire some manual iteration on successive power flow cases. Most commercially available programsdo not have variable reactance models for load flow simulations.

Limits need to be considered in order to obtain correct power flow solutions. Initially, the system studyshall be focused on determining suitable device ratings to achieve the desired performance. At thisstage, reactance limits can be fixed. The results of system simulations should then be used to determineactual device ratings, which are then reflected in reactance limits that are a function of the maximumallowed continuous capacitor voltage (as per Figure 5), which is derived from the line current (assuggested by Figure B.2). The power flow studies should establish the continuous and 30 minreactance, current, and voltage ratings. These ratings are then included in the device specification. Theuse of one or more fixed reactances may be sufficient for many cases.

B.2.2 Modeling for stability studies

For these types of studies (dynamic, transient, and eigenvalue analysis), the TCSC device shall bemodeled to include its dynamic power frequency characteristics. Therefore, it is important to provide adetailed model for the TCSC and its controller (Zhou and Liang [B29]).


Figure B.2—TCSC models for power flow studies



WITHDRAWN

The TCSC power equipment (i.e., the actual reactance element and firing controls) can be representedrelatively simply in the stability program. Normally, the firing control model can be greatly simplifiedfor electromechanical and eigenvalue analysis, due to the small time constants. In this case, the firingcontrol system can be represented by a first-order filter with a time constant of the order of 50ms (seeModel A in Figure B.3). Most commercially available programs provide this model, but do not imposevoltage and current dependent reactance limits for stability simulations. Stability studies shouldestablish the dynamic (e.g., 10 s) ratings of the device for inclusion in the specification. Considerablecare shall be exercised by the user in interpreting results.

If more accurate studies are desired, the firing control modeling should be considered as it couldinfluence stability especially when dealing with oscillation modes with frequencies higher than 1.0Hz.In this case, the TCSC is modeled as current injection, which is a function of the line current, the firingangle, and the capacitor voltage (see Model B in Figure B.3). Such models are not normally availablein commercial stability software.

The TCSC control, which provides a reactance order input to the device model (Figure B.3), can berelatively simple or can be quite complex, depending on the requirements of the application.

Controls for power system stability in response to large disturbances are generally treated as twoseparate issues. Transient or first-swing stability deals with the system recovery during the first swing.Damping of subsequent oscillations is the second aspect and is commonly known as dynamic stability.

To improve first-swing stability, it is necessary to increase the system synchronizing power. Oneapproach is to have the maximum amount of series compensation in operation during normaloperation to minimize the initial angle across the system. This is not always possible, however, due tosteady-state power flow schedules and voltage control requirements. Hence, it is sometimes essential tohave a portion of the series compensation, which can be inserted following a contingency. Switchingcould be made on the basis of measured power, line current, or bus voltage, or it could be based ondiscrete inputs such as breaker status. The dynamic modeling required for conceptual design of suchopen-loop controls can be relatively simple, with implementation being effected by imposing open-loop switching during time simulations. More detailed logic can be included, as necessary, whenfunctional design simulations are run.

To improve damping, the line reactance shall be modulated in opposition with the power swings. Thiscan be performed by a properly designed control function. The input shall be a signal related to powerswings, and the controller has to be adjusted to give a correct gain and phase angle relationshipbetween output and input.

Having these aspects in mind, an example generic controller for stability enhancement is shown inFigure B.4. The ‘‘transient stability function’’ may act initially for large disturbance, leading (forexample) to the maximum compensation level for fixed time duration (Ta). On removal of a discrete(open loop) stability signal, control would be transferred to the ‘‘damping loop,’’ which would be incharge of damping subsequent power oscillations.


Xmax (I, V )

Xmin (I, V )

XORDER XORDER

X X

I (α, IL, VC)

Model A Model B

Figure B.3—TCSC network elements (firing control) modeling



WITHDRAWN

The primary control might be either current (power) control, reactance control, or even voltagecontrol. The supplementary signal of the damping loop (Xd) is added to the output of the primarycontrol. Such an alternative scheme has the advantage of a faster response since stabilization action isbeing applied directly on the ordered reactance.

All of the functions shown in Figure B.4 are software, and not physical limitations or requirements ofTCSC. This means that other designs, structures, and functionalities are possible.

B.2.3 Modeling for SSR studies

Implementation details of specific control schemes will have a significant impact on SSR performanceof TCSC. Therefore, the planning study should determine the maximum percentage of FSC that ispossible without SSR problems. If higher compensation is needed in the system, then the additionalreactance could be provided by a TCSC. Transients and frequency domain modeling of TCSC for SSRshould be performed by the supplier, using power system and detailed turbine–generator models.

B.2.4 Transients (EMTP/ATP) modeling

For electromagnetic transient analyses, which are used to investigate high-frequency phenomena, amuch more detailed model is necessary (Zhu et al. [B30]). It is essential to represent not only thecontrol system, but also the firing pulse generation scheme. The primary difference from the stabilitystudies is that the output of the control system is the firing angle. The network elements of the TCSC


Xref

Xpi XORDER

XORDER

Xmax (t)

Xmax (t)

XdKd

Xs

Ta

Xmin (t)

Ki + sKp

s

1 + sTf

1

1 + sTm

1 + sTw

sTw

1

Figure B.4—Possible generic high-level control for stability analysis



WITHDRAWN equipment can be fully represented as inductors and capacitors including the thyristor valves andprotective metal oxide varistors. An electromagnetic transient study could focus on equipmentdynamic performance, potential control system interactions, or switching surges and temporaryovervoltages. Therefore, fundamental protective actions shall also be modeled. A generic blockdiagram of the basic control structure of a TCSC device modeled in the alternative transient program(ATP) or EMTP is shown in Figure B.5. Somewhat different measurements (e.g., capacitor voltage isoften measured) and control structures (e.g., there are various means of translating reactance order topulses) shall be found for different manufacturers and implementations.

The device is divided into three different subsystems: TCSC power circuit (or network elements);measurement and control systems; synchronizing and firing systems. The power circuit consists of acapacitor bank (C) in parallel with a thyristor-controlled reactor (TCR represented by L in Figure B.5)and the overvoltage protection device formed by the varistor. The thyristor valve also features asnubber circuit.

Use of a generic transients model needs to be limited to initial investigation of these phenomena, sincedetails of implementation are specific to the various manufacturers. These details have the potential toimpact significantly on simulation results and will tend to be customized for each application.


��

��

��

��

��

��

Figure B.5—Block diagram of TCSC model for EMTP/ATP



WITHDRAWN B.3 Legend

Table B.2 describes the variables used in Figure B.1, Figure B.2, Figure B.3, Figure B.4, andFigure B.5.


Table B.2—Legend

Figure Variable Description

B.1, B.4 Ref Reference value (set point)

B.1, B.3, B.4, B.5 XORDER Reactance order

B.2 XFSC Reactance (fixed series compensation)

B.2, B.3 Xmin(I,V), Xmax(I,V) Minimum and maximum steady-state reactance limit as afunction of line current (I) and capacitor voltage (V)

B.3 I(a, IL, VC) Current as a function of firing angle (a), line current (IL) andcapacitor voltage (VC)

B.3, B.4 s Mathematical notation for a complex variable

B.3, B.4 Tf Equivalent reactance control time constant

B.3, B.5 X Reactance

B.4 Kd, Ki, Kp Damping (Kd), integral (Ki), and proportional (Kp) gains forflow controller

B.4 L1, L2, L3, L4,T1, T2, T3, T4

Damping controller conditioning signal limits (L1, L2, L3, L4)and variables (T1, T2, T3, T4)

B.4 Ta Time (duration of the operation at maximum capacitivereactance)

B.4 Tm Power or current transducer time constant

B.4 Tw Damping input signal rate time constant

B.4, B.5 Xd Damping reactance order

B.4 Xmin(t), Xmax(t) Minimum and maximum reactance limit as a function of linecurrent and time

B.4 Xpi Flow or current control reactance order

B.4 Xref Reference reactance order

B.4 Xs Transient stabilizing reactance signal (overrides continuouscontrols)

B.5 a Firing angle

B.5 C Series capacitor

B.5 IL Line current

B.5 IM Measured line current

B.5 Iref Reference current

B.5 L Thyristor reactor

B.5 PI Proportional integrator

B.5 VL Measured line voltage

B.5 XManual Manual reactance order



WITHDRAWN Annex C

(normative)

Summary outline of TCSC specification

This narrative annex provides a summary outline of recommended items that should be consideredwhen preparing a TCSC specification. Terms and conditions forming the commercial part of a TCSCspecification are outside the scope of this recommended practice.

C.1 General

The purchaser should specify general conditions and objectives for which the TCSC installation is tobe designed and operated including the following:

a) Project scope: The purchaser should define the scope of supply to be provided by the purchaserand supplier for the overall TCSC project (see Clause 14).

b) List of applicable standards: The purchaser should provide a summary list of standards forwhich the TCSC installation is to be designed, manufactured, and tested. Each of the listedstandards should be referenced, where applicable, in the appropriate clauses of the TCSCspecification.

c) Site service conditions: The purchaser should specify the TCSC installation site serviceconditions (see Clause 4).

C.2 AC transmission system

The purchaser should specify the electrical characteristics of the transmission line being compensatedand associated ac transmission system including the following:

a) Rated line-to-line voltage:

1) Continuous2) Maximum operating voltage and duration

b) Rated frequency:

1) Continuous power frequency and steady-state variations2) Transient power frequency variations and duration

c) Electrical insulation levels (phase-to-ground):

1) Basic impulse level (BIL)2) Wet switching surge withstand level3) Power frequency withstand voltage (1 min)

d) System data:The purchaser should provide transmission line data and system information adequatefor the supplier to perform specified studies and design of the TCSC equipment (see 5.4and 5.5).




WITHDRAWN C.3 TCSC

C.3.1 Operational objectives

The purchaser should specify any special operating conditions and system events (see 5.5) for whichthe TCSC components and equipment are to be designed and operated including radio influencevoltage level, corona level, and audible noise level.

C.3.2 TCSC ratings

The purchaser should specify the TCSC continuous, bypass, temporary overload, and dynamicoverload, and duty cycle operating requirements (see 5.3 and 5.4). It is recommended that theseparameters be presented in graphical form similar to Figure 5 and Figure 6. The following operatingparameters should be defined for capacitive reactance and bypass modes of operation, as these can bevery different.

C.3.2.1 Capacitive reactance operating parameters

a) Continuous operation:

1) Maximum rated line current (IR)2) Maximum rated voltage across TCSC (VR)3) Rated reactance (XR) or reactance range4) Rated three-phase Mvar (3IR

2XR)5) Reactance (XC) with thyristor valves blocked6) Minimum current for which the thyristor valve remains operational (IMIN)7) Specify if the reactance control is required to be smooth (stepless) over the specified range

b) Temporary overload operation (typically � 30min):

1) Maximum current (IT)2) Duration of overload and frequency of occurrence3) Maximum voltage across TCSC (VT)4) Maximum overload line current reactance (XT) or reactance range5) Specify if the reactance control is required to be smooth (stepless) over the specified range

c) Dynamic overload operation (typically � 10 s):

1) Maximum current (ID)2) Duration of overload and frequency of occurrence3) Maximum voltage across TCSC (VD) without thyristor bypass or significant varistor

conduction4) Specify if the impedance control is required to be smooth (stepless) over the specified

range

C.3.2.2 Bypass operation parameters

a) Continuous operation:

1) Maximum current (IBR)2) Minimum current for which the thyristor valve remains operational (IMIN)

b) Temporary overload operation (typically � 30min):

1) Maximum current (IBT)2) Duration of overload




WITHDRAWN c) Dynamic overload operation (typically � 10 s):

1) Maximum current (IBD)2) Duration of overload

d) Fault current:

1) Maximum fault current (IF)2) Duration of fault current3) Fault current duty cycle (see C.3.2.3)

C.3.2.3 Duty cycles

It is recommended that the desired duty cycle requirements for the TCSC equipment is clearly definedby the purchaser. Some of the considerations are discussed in Clause 5.4. Figure C.1, Figure C.2,and Figure C.3 depict three typical duty cycles. For each, a graphical depiction of the time line of theduty cycle is provided along with the factors to be considered for each part of the cycle. For brevity,only faults cleared by the normal operation of the line protection and the line circuit breakers arepresented.

a) Permanent fault on an external line section with high-speed reclosing

NOTESt1—TCSC is operating at IR and XR prior to the external fault.t2—A normally cleared external fault occurs. The purchaser should specify the following:

a) Duration of faultb) The type of bypass permitted (e.g., varistor, bypass gap, thyristor valve, bypass switch)

c) Power system impedances so that the duty to the bypassing equipment can be determinedd) If the TCSC is to be inserted prior to, or following, line reclosuree) The response time of the TCSC following re-establishment of line current

f) Correct operation for both the close-in and remote faults shall be considered


Figure C.1—Permanent fault on an external line section with high-speed reclosing



WITHDRAWN t3—If reclosing is practiced, the purchaser should specify:

a) The time between the clearing of the first fault and reclosing of the external line

b) The operating current and desired range of X(a)

t4—The external line is reclosed into a permanent fault. The purchaser should specify the same type of information as wasdefined for the first fault.

t5—A power system swing occurs after external fault clearing. The purchaser should define the following:

a) The shape of the swing current in graphical or tabular form with a 1 ms resolutionb) The desired function and range of X(a)c) The maximum VD required

t6—An overload follows the swing condition. The purchaser should specify the following:

a) The duration of the overload

b) The overload current and the desired range of X(a)

t7— TCSC resumes operating at IR and XR.

b) Permenant internal line section fault with high-speed reclosing

NOTESt1—TCSC is operating at IR and XR prior to the internal fault.t2—A normally cleared internal fault occurs. The purchaser should specify the following:

a) Duration of fault

b) The type of bypass permitted (e.g., varistor, bypass gap, thyristor valve, bypass switch)c) Power system impedances so that the duty to the bypassing equipment can be determinedd) If the TCSC is to be inserted prior to, or following, line reclosure

e) The response time of the TCSC following re-establishment of line current

t3—If reclosing is practiced, the purchaser should specify the time between the clearing of the first fault and reclosing of the line.t4—The line is reclosed into a permanent fault. The purchaser should specify the same type of information as was defined for the

first fault.t5—The line will remain out of service for an extended period of time that should be specified by the purchaser.t6—The line is reclosed and the TCSC resumes operating at IR and XR.


Figure C.2—Permanent internal line section fault with high-speed reclosing



WITHDRAWN c) Temporary internal line section fault with high-speed reclosing

NOTESt1—TCSC is operating at IR and XR prior to the internal fault.t2—A normal cleared fault occurs. The purchaser should specify the following:

a) Duration of faultb) The type of bypass permitted (e.g., varistor, bypass gap, thyristor valve, bypass switch)c) Power system impedances so that the duty to the bypassing equipment can be determined

t3—If reclosing is practiced, the purchaser should specify the following:

a) The time between the clearing of the first fault and reclosing of the external line

b) If the TCSC is to be inserted prior to, or following, line reclosurec) The response time of the TCSC following re-establishment of line current

t4—A power system swing occurs after fault clearing. The swing current in the TCSC could be different than for the external faultsituation. The purchaser should define the following:

a) The shape of the swing current in graphical or tabular form with a 1 ms resolutionb) The desired function and range of X(a)c) The maximum VD required

t5—TCSC resumes operating at IR and XR.

C.4 Thyristor valves

The thyristor valves should be designed by the supplier to meet the operating and rating requirementsof the TCSC installation. Design features that the purchaser should consider when specifying theTCSC thyristor valves include the following:

a) Maintenance

1) Tools, handling, and facilities for maintenance2) Time between maintenance periods


Figure C.3—Temporary internal line section fault with high-speed reclosing



WITHDRAWN 3) Time to replace an individual thyristor level

b) Monitoring and diagnostic provisions indicating the number and position of a failed thyristorc) Redundancy factorsd) Guaranteed maximum annual failure ratee) Design calculations for insulation coordination and varistor ratingsf) Design calculations for maximum junction temperatureg) Current and voltage capabilities (see 6.1)h) Control features (see 6.2)i) Cooling system electrical requirements (see 6.3)j) Mechanical design features (see 6.4)k) Design tests (see 6.5.1)l) Production tests (see 6.5.2)

C.5 Capacitors and reactors

See Clause 7.

C.6 TCSC control and protection

The purchaser should specify the TCSC control and protection requirements (see Clause 8).

C.7 Layout

The purchaser should specify the general layout requirements for the TCSC installation including thesubstation yard, platform assemblies, and control building (see Clause 9).

C.8 Safety

The purchaser should specify the personnel and equipment safety requirements for the TCSCinstallation (see Clause 10).

C.9 Testing and commissioning

The purchaser should specify the testing and commissioning requirements for the TCSC installation(see Clause 11).

C.10 Losses and loss evaluation

The purchaser shall specify the loss evaluation factors that shall be used to establish the cost of powerlosses for the TCSC installation (see Clause 12). Additionally, contract incentive provisions forsupplier performance guarantees related to losses should be clearly stated by the purchaser (asapplicable).

C.11 Reliability, availability, and maintainability

The purchaser should specify the reliability, availability, and maintenance requirements for the TCSCinstallation including supplier-furnished spare parts (see Clause 13). Additionally, contract incentive




WITHDRAWN provisions for supplier performance guarantees related to reliability and availability should be clearlystated by the purchaser (as applicable).

C.12 Training

The purchaser should specify the training requirements for the TCSC installation (see Clause 15).

C.13 Documentation

The purchaser should specify the documentation requirements for the TCSC installation including thefollowing:

a) Drawings and data provided by the purchaser should be listed in the specification (see 16.2).b) Drawings, data, and submittal requirements to be provided by the supplier should be stated in

the specification by the purchaser including purchaser approval requirements (see 16.3).


IEEEStd 1534-2002


ieee std 1534 eee standards ieee standards substations

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