power system studies

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Power System Studies/Power System

Analysis/Engineering

Source: http://www.powerapps.org/


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Contents

Contents..................................................................................................................... 2

Power System Studies /Analysis /Engineering ...........................................................4

Data Needed for Power System Studies.....................................................................5

Load Flow/Power Flow Studies and Analysis...............................................................6

Applications of Power Flow Study and Analysis.......................................................7

The following general criteria of acceptability of design is used in power flow

studies.................................................................................................................. 7

Contingency Ranking and Evaluation - System Security and Adequacy Evaluation 8

General Features of PowerApps Power Flow Software.............................................8

Introduction .......................................................................................................... 38

Description of the system......................................................................................39

Insulation Coordination Study............................................................................... 39

Power Frequency Overvoltage Studies..................................................................40

Switching Frequency, Fast Front, Very Fast Front Overvoltages...........................41

Modeling of Sub-sea cable for EMTP studies..........................................................41

Sample Simulation Results and Plots.....................................................................42

Conclusions/Recommendations.............................................................................42


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Power System Studies /Analysis /Engineering

Power System Studies refers to the study of power evacuation from generation to loads, undercontrol, protection and supervision; and under normal or contingency conditions; under various

expected operation scenarios; capturing the behaviour of the electrical network, its elements,

its control, protection and their response under different time frames, spanning few a micro

seconds to several hours or even years of time.

These studies may also be classified as Static, Dynamic or Transient, depending on the

mathematical models used in analysis and the time frame of examination of the behavior of the

power system under consideration.

The nature of the studies and their objectives may vary for different types of electrical network[or power systems] and the problems being analyzed, with possible different criteria. Thus a

study for a transmission system , a distribution system or an Industrial network may not all have

identical perspective, even though the type of analysis modules used in analyzing them are same.

These studies may fulfill the objectives ofsystem planning, system design, system protection

and control, developing system operation strategies, commercial and technical evaluation

and feasibility studies, solutions for problems faced during system operation.

These studies are pre-requisites forany new system, for any new renovation, modernization

and expansion plans, and also for existing systems for arriving at solution for problems

faced in the operation.

As a rule, it is mandatory to perform the power system studies, where interconnection of two

different systems is proposed. For example, interconnection of a industrial load to a distributioncompany, requires that standard set of studies to be performed, typically covering, the load flow,

short circuit, relay coordination, harmonic analysis, motor starting studies and stability studies as

applicable.

List of Power System Studies/Analysis

The power system study group has performed widest possible range of power system studies as

follows. The studies cover planning, engineering, economic aspects of power system, design,

operation, control and protection and uses appropriate static, dynamic or transient study modelsfor power systems.

Power Flow Studies.

Short Circuit Studies (Conventional/IEC909/ANSI/IEEE/G74).

Contingency Studies [Ranking and Evaluation].
http://www.powerapps.org/PAES_ShortCircuit.aspxhttp://www.powerapps.org/PAES_ShortCircuit.aspxhttp://www.powerapps.org/PAES_LoadFlow.aspx#Contingencyhttp://www.powerapps.org/PAES_LoadFlow.aspx#Contingencyhttp://www.powerapps.org/PAES_LoadFlow.aspx#Contingencyhttp://www.powerapps.org/PAES_ShortCircuit.aspx


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Optimal Power Flow.

Reactive Power Optimization.

Capacitor Locations and Sizing.

Static/Dynamic Voltage Stability Analysis.

Transient Stability Analysis (Large Signal Performance).

Dynamic Stability Analysis (Small Signal Performance).

Power System Stabilizer Applications.

Protection System Studies (Overcurrent phase and earth fault, High set, Differential,

Distance, Frequency, Voltage).

Equipment Protection Applications (Transformers, Transmission lines, Motors,

Generators, Bus Protection).

Harmonic Measurements, Analysis and Filter Design.

Switching Transient Studies.

Insulation Coordination.

Motor Starting Studies.

Evaluation of energy transactions in de-regulated market. Energy pricing, Wheeling andbanking charges, Transmission and Distribution Pricing, Grid Support charges.

Ground Mat Design.

Energy Audit Services.

Reliability Evaluation.

Long term energy and demand forecast along with associated system/finance/commercial

planning.

EMTP, Line Constants, Parameter Evaluation, Insulation Coordination.

Power quality related studies

Power evacuation studies

Switch Yard and Substation Design

Data Needed for Power System Studies
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Introduction

This document provides the general data requirements for power system studies. For specificsystem studies additional information may be needed and the same will be sought by the

consultants. Some of the requirements specified may not be needed for all the studies.

General Requirements

1. Description of the system for which the electrical system studies are needed2. Description of the system study objectives

3. Complete single line diagram of the system, showing generators, loads, transformers,cables, overhead lines, shunt capacitors, shunt reactors, series capacitors, series reactors,

motors, SVCs, HVDC elements, Breakers, relays, CTs, PTs, Isolators and any other

relevant critical circuit elements.

4. Clear identification of the existing and proposed system modifications if any, on the

single line diagrams.

5. Technical Datasheets of the generators, AVR, Speed Governor, Prime Mover. The data

sheets for generator controllers should be suitable for transient and dynamic stability

simulations. V/F capability curves, negative sequence current withstand capabilitycurves, description of various protections.

6. Technical data sheets for transformers along with the thermal withstand capability curves,V/F capability curves.

7. Technical data sheets for HT motors with no load and blocked rotor test results and motorcharacteristics (performance curves supplied by the manufacturer). Motor starting method

and starting time.

8. Technical data sheets, catalogues, application guides for protective relays

9. Plant operating philosophy for various operating conditions (peak demand, minimum

demand, with or without grid support, during maintenance/ equipment outage conditions)along with bus-wise generation and load details.

10. Details of the cables, over head lines, there impedance parameters, length, number ofruns

11. Technical data sheets for shunt capacitors, shunt reactors, SVCs, harmonic filters, series

capacitors, series reactors

Load Flow/Power Flow Studies and Analysis


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Power flow analysis/studies is the preliminary step used in anyPower Evacuation Studies.

Power flow calculations provide active and reactive power flows and bus voltage magnitude and

their phase angle at all the buses for a specified power system configuration and operating

condition subject to the generation and/or regulating capabilities of generators, synchronouscondensers, static var compensators, HVDC controls, FACTS controllers, tap changing under

load transformers and specified net interchange between individual operating systems (utilities).

This information is essential for the continuous evaluation of the current performance of a powersystem and for analyzing the effectiveness of alternative plans for system expansion to meet

increased load demand. These analyses require the calculation of numerous power flow cases for

both normal, and emergency (contingency) operating conditions. The output from power flow

studies often provide the initial conditions needed for other analysis, such as short circuit studies,transient stability, economic dispatch, dynamic stability studies.

Applications of Power Flow Study and Analysis

Power flow study has the following applications

1. Transmission expansion planning , operation planning2. Distribution expansion planning , operation planning

3. Industrial/Commercial distribution system planning, operational planning

4. Network interconnection, Grid interconnection studies

5. Evaluation of energy transactions between various stake holders

6. Energy audit to accurately determine network losses and estimate billing losses if any

7. Sizing of transformers, cables, overhead lines, transformer tap ranges, shunt capacitors, shunt

reactors, reactive power management, FACTS devices, HVDC operation

8. System security assessment via static contingency studies

9. Decision making tool in operation planning and operation of the system in load dispatch center

10. Motor starting studies using load flow type analysis, where the starting impedance of the

Induction motor is modeled as constant impedance model with starting impedance.

11. Evaluation of static voltage stability using load flow technique

The following general criteria of acceptability of design is used in power flow studies

a. Voltage Drop at all buses should be within +/- 5% of the nominal rating for all operating

conditions considered
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b. No over load conditions of any electrical circuits for all operating conditions considered

c. Reactive power generation/import/export to be within specified limits for all operating conditions

considered

d. Ensuring quality power supply to all loads, under specified contingency conditions, as per design

philosophy adopted.

The following study cases/ power flow outputs are generally considered in power flow studies

a. Extreme operating conditions of maximum and minimum loading conditions will be considered

to check the adequacy of the network, even though some of these conditions may not exist during

normal operation

b. Contingency conditions such as outage of lines, transformers, generators will be considered and

network adequacy for power evacuation will be assessed

c. Operating solutions such as transformer taps, Generator Excitation, shunt reactive power

compensations will be provided as needed.

d. Recommendations for strengthening and equipment upgradations will be provided to meet

specific operating requirements.

e. Summary of load flow studies and concise reports in tabular formats and single line diagram

formats will be provided, along with the summary of recommendations

Contingency Ranking and Evaluation - System Security and

Adequacy Evaluation

Contingency evaluation studies typically refers to evaluation of network adequacy and security

under credible network element outage conditions. Typically outage of important transmissionlines , transformers, generating units are usually considered in the evaluation. The evaluation is

carried out by using static as well as dynamic analytical tools such as load flow analysis and

transient stability analysis. Real time control and monitoring solutions in enercy control centers

or energy management systems or load dispatch centers usually use an algorithm calledcontingency ranking algorithm to shortlist credible contingencies for real time evaluation and

control of power systems. Often contingency ranking algorithm will use some approximate and

fast load flow type algorithms from a list of contingencies and rank them in the decreasing orderof severity. This ordered or ranked list will be considered for a detailed contingency evaluation

to assess system security.

General Features of PowerApps Power Flow Software


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Power Flow is the analysis module of PowerApps dedicated to power flow analysis in three-

phase electric power networks. It is equipped with powerful analytical options and alternative

solution techniques.

Gauss-Seidel.

Newton-Raphson.

Fast-Decoupled.

AC/DC Load Flow, FACTS devices.

Load flow solution of multiple-islanded systems. The solution is available for each of the islands

having a reference (slack) node. The reference node is automatically identified by the algorithm

as the largest generator node in each island.

Limit violation reports, summary reports.

Unbalalanced 3 phase load flow, including 1 and 2 phase load flow for lines drawn separately

from a 3 phase supply point.

Choice of objectives for the OPF/RPO (Transmission loss minimization, Voltage Stability

improvement, Removal of operating violations, Economic dispatch).

Optimal Load Flow.

OPF/RPO control options are active power injections, reactive power injections, shuntcompensations, series compensations, phase shifters, transformer taps.

OPF/RPO sensitivity calculations with respect to the performance objective provides information

for suitable location of shunt reactive power compensation and also identifies most effective

controllers for optimization.

No limits on the number of study cases and related reports in a single execution of the program

Short Circuit Studies, Fault Calculations

Short circuit calculations provide currents and voltages on a power system during faultconditions. This information is required to design an adequate protective relaying system and to

determine interrupting requirements for circuit breakers at each switching location. Fault

conditions can be balanced or un-balanced shunt faults or series (open conductor) faults. Often

information about contributions to a fault from rotating machines such synchronous machines,large motors would be required as a function of time to determine making and breaking

requirements. Fault calculations may consider or ignore pre-fault power flow conditions. Short

Circuit is the PowerApps analysis module dedicated to simulating fault conditions in three-phaseelectric power systems. User friendly data entry, a multitude of reports and flexibility in applying

all industry-accepted standards are features that make it an Indispensable tool for these very

common and important system studies. PowerApps Short Circuit Module adheres to NorthAmerican ANSI C37.5, ANSI C37.010, ANSI C37.13 and International IEC-60909 guidelines. It

also supports conventional short-circuit studies without reference to any particular standards.


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Short circuit studies provide post fault bus voltages at different busbars in the network for a fault

at any one of the location in the network. These results are typically given as fault MVAs, fault

currents in kA at different bus bars and fault contributions from adjacent bus sections to the fault,on a single line diagram for various operating conditions. Short circuit studies for minimum fault

level condition at the main switch board may be of interest in relay coordination to check,

whether relays can distinguish between the maximum load currents and minimum fault currents.In the event, the minimum fault currents in the relays are very close to the maximum load

currents, it may be necessary to suggest voltage restraint for relays to ensure that the relays will

operate only for fault conditions and not for healthy full load conditions.

The deliverables from the short circuit studies will include the following

-Tabular report of conventional short circuit levels at all buses

-Tabular reports of Making/Breaking Current levels at all the buses

-Report on single line diagrams showing fault levels, fault kA for both conventional and IEC60909 type calculations

-Recommendations with respect to operating strategy, to limit short circuit levels where needed

General Features of Short Circuit Study/Calculation

Software

Fault levels for asymmetrical and symmetrical faults including bolted faults.

ANSI/IEEE standards.

IEC standards including 363 and 909.

G74 British standard, a computer algorithm based standard for IEC 909 standard. IEC909 standard specified multiplication factors based on hand calculation procedures and

simplifying assumptions.

Short circuit analysis of multiple-islanded systems with solution for each of the islands.

Default flat 1.0 pu positive sequence bus voltage based calculations.

Option to consider pre-fault bus voltages from load flow along with the sequence

impedances for loads.


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Automatic one line diagram creation.

Multiple case studies in single execution of the program for different networkconfigurations and/or different source impedances or ratings.

Automatic generation of reports for all the specified study cases on the single line

diagram.

Induction motor models.

Fault calculations for network with multiple islands with sources in each island.

Detailed system wide post fault bus voltages and flows for specified bus faults along withimpedance seen at each relay locations.

Output contains, detailed phase quantities, sequence quantities of voltages, currents,driving point impedances, transfer impedances, contribution from sources, and

contribution from adjacent buses.

Results of fault calculations with mutual coupling matches perfectly with published

examples.


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Reactive Power Optimization[RPO], Optimal

Power Flow [OPF], Economic Dispatch[ED],

Available Transfer Capability [ATC]

Calculations

The power flow solution calculates power flows and determines bus voltages at an operating

point for a given network configuration and generation and load specifications. However, it is

left to the engineering judgement of the system planner to determine optimum way of systemoperation considering

- Operating objectives


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- Operating constraints [Commercial and Security Constraints] and

- Equipment capability constraints.

Such an exercise using load flow tool is very tedious and time consuming for a practical power

system with large number of operating controls and constraints.

A properly designed optimal power flow [OPF] solution provides the best and most optimum

practical solution to achieve improvement in a single or multiple hierarchical objectives while

respecting various constraints on the system operation. An OPF can determine the most effective

subset of controls and their solution for a given operating condition to improve the specifiedobjectives. OPF can consider different objectives for improvement such as transmission loss

minimization, voltage stability improvement and minimization of system operating cost.

OPF/RPO analysis module of PowerApps is based on the Primal-dual LP programming approach

and has the following features:

Newton-Raphson load flow for solution at an operating point.

OPF/RPO solution of multiple-islanded systems. The solution is available for each of theislands having a reference (slack) node. The reference node is automatically identified by

the algorithm as the largest generator node in each island.

Choice of objectives for the OPF/RPO (Transmission loss minimization, Voltage

Stability improvement, Removal of operating violations, Economic dispatch, ATC

calculations).

Optimal load flow as per selected objectives and specified constraints

OPF/RPO control options are active power injections, reactive power injections, shuntcompensations, series compensations, phase shifters, transformer taps.

OPF/RPO sensitivity calculations with respect to the performance objective providesinformation for suitable location of shunt reactive power compensation and also identifies

most effective controllers for optimization.

No limits on the number of study cases and related reports in a single execution of the

program.

Optimal_Power_Flow.pdf

Convergence Characteristics of the PowerApps Optimal Power Flow[OPF]

Static Voltage StabilityThis is a stability phenomenon, where the power system looses its ability to control load bus

voltage due to various reasons. This phenomenon can lead to failure of the total or partial powersystem due to interventions of various control and protection actions.
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The reasons for voltage instability could be

-Failure to provide necessary power support to the loads as a consequence of power transfer

limit. The power transfer limit is determined not only by the bus voltage phase angle, butalso by bus voltage magnitude

-Failure to meet power requirements due to equipments reaching their control and operating

limits. Examples are transformer tap limits, generator reactive power supply capabilities.-Inconsistency in the load power requirements as function of bus voltage and power supply

characteristics.

PowerApps provides various analytical tools for assessment of static voltage stability using loadflow solution or output from static state estimation. Further the reactive power optimization

algorithm provides a method of improving static voltage stability. The analytical tools are

1. V-P (nose) curves or PV curves

2. Sensitivity Indices. Sensitivity of bus voltage magnitude for active (P) and reactive (Q)injection at a bus.

3. Sensitivity of net reactive power generation for a given bus reactive power injection.

4. Minimum Singular Value Decomposition of the complete load flow Jacobian as well us

reduced Jacobian formulations. [ P.A.Lof, T.Smed, G.Andersson, D.J.Hill Two IEEETransaction publications, 1992, 1993]. Further, identification of critical buses based on

left and right singular vectors are also implemented in PowerApps.5. Voltage Stability Index L proposed by P.Kessel and H.Glavitsch. [ IEEE Transactions on

Power Delivery, 1986].

6. Static Voltage Stability Evaluation using relative bus voltage phasors at an operatingpoint given by load flow solution or static state estimation.. [A New and Fast Technique

for Voltage Stability Analysis of a Grid Network Using System Voltage Space",

Published in International Journal of Electrical Power & Energy Systems, Elsevier

Science Ltd. UK .]7. Improvements in static voltage stability using a reactive power optimization tool.

[Optimal Static Voltage Stability Improvement Using a Numerically Stable SLP

Algorithm, for Real Time Applications", Published in International Journal of ElectricalPower & Energy Systems, Elsevier Science Ltd. UK ]

Transient Stability Analysis

The recovery of a power system subjected to a severe large disturbance is of interest to system

planners and operators. Typically the system must be designed and operated in such a way that aspecified number of credible contingencies do not result in failure of quality and continuity of

power supply to the loads. This calls for accurate calculation of the system dynamic behavior,which includes the electro-mechanical dynamic characteristics of the rotating machines,

generator controls, static var compensators, loads, protective systems and other controls.

Transient stability analysis can be used for dynamic analysis over time periods from few secondsto few minutes depending on the time constants of the dynamic phenomenon modeled. Transient

Stability Analysis is the PowerApps simulation module dedicated to simulating


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electromechanical transients in three phase electric power systems. It features an extensive

library of equipment and controller models, the capability to include user-defined controls, a

very flexible user-interface and powerful graphics. Transient Stability Analysis module utilizesthe simultaneous implicit trapezoidal integration solution technique for network, machine and

controller equations. The program supports the capability to test the step response of controllers

and User Defined Modeling for system equipment and controllers.

General Features of Transient Stability Analysis

Transient models of excitation systems, turbine governors, static-var compensators,

power system stabilizers and HVDC controllers.

Load shedding / islanded operation.

Transient stability analysis of multiple-islanded systems with solution for each of the

islands.

Choice of generator models. From simple classical generators with constant voltage

behind transient reactance to modelling detailed synchronous machines with variable

voltages behind sub-transient reactances.

Standard IEEE excitation system models and turbine and governor models.

Commercial excitation models and governor models.

Models for power system stabilizers and different stabilizing signals.

Modelling load characteristics similar to that in the load flow analysis.

Modelling load characteristics as function of frequency.

Dynamic models of Induction motor and its load.

Motor starting studies. Motor modelling by their equivalent circuits or by the measured

response during starting along with mathematical model for load torque as function of

speed.

Under frequency/Under Voltage relay operation simulation.

Load shedding.

Islanded operation.

Element opening/closing.

Loss of generators.

Multiple transient stability disturbance scenarios for each base case load flow study. Note

that, multiple load flow case studies can be performed followed by multiple transientstability simulations for each load flow study case.


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Plots of selected bus frequencies and bus voltages. Note bus frequencies are different

from generator frequencies.

Reports and Recommendations from Transient Stability

Studies

1. Plots of Dynamic response of Generator rotor angles, frequencies, power outputs,

voltages, excitation system outputs, governor-prime mover outputs2. Plots of Line Flows, transformer flows, bus voltages, bus frequencies

3. Plots of Motor dynamic variables where required

4. Plots of the system variables that are of interest from protection point of view [example

frequencies, distances seen from distance relays, fault currents seen from overcurrent

relays etc]

5. Recommendation related to protection and control, operating strategy, Control settings of

equipments [for example power system stabilizer, relay settings, load shedding schmesetc], based on various study cases considered


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Dynamic Stability Analysis

The dynamic behaviour of power systems subjected normal power impacts is influenced by thefollowing factors:


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The system load level.

The network characteristics.

The Generator and its controller characteristics.

The load characteristics.

The system is dynamically stable if the oscillatory response following a perturbation quicklysettles down to a new stable operating point without sustained oscillations. These studies are

typically carried out using linearized model of the system.

General Features of Dynamic Stability Analysis

Component modelling similar to Transient Stability Studies. Linearized model of network algebraic equations and first order differential equations

used at an operating point.

Eigen values analysis used for the evaluation of the system stability.

Option for time domain simulation with the linearized model and with specifiedperturbation.

Transfer function approach with single machine, infinite bus models.

Can be executed for multiple islanded systems and for multiple load flow study cases.

Options for root locus plots, Bode plots for simple single machine infinite bus models.


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Power System Stabilizer Applications

The dynamic stability of a system can be improved by providing suitably tuned power system

stabilizers on selected generators to provide damping to critical oscillatory modes. Suitably tunedPower System Stabilizers (PSS), will introduce a component of electrical torque in phase with

generator rotor speed deviations resulting in damping of low frequency power oscillations in

which the generators are participating. The input to stabilizer signal may be one of the locallyavailable signal such as changes in rotor speed, rotor frequency, accelerating power or any other

suitable signal. This stabilizing signal is compensated for phase and gain to result in adequate

component of electrical torque that results in damping of rotor oscillations and thereby enhancepower transmission and generation capabilities. State-space techniques described under Dynamic


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Stability Studies or classical control theory such as Bode plots, root locus techniques can be used

to determine suitable parameters for power system stabilizers.The design can then be verified

with a transient stability analysis for practical system disturbances.

A Typical Control Schematic Diagram of Power System Stabilizer

Power System Protection Studies and Relay

Coordination

See: CASE STUDY : Protection Co-ordination Study

In any power system netowrk, protection should be designed such that protective relays isolatethe faulted portion of the network at the earliest, to prevent equipment damage, injury tooperators and to ensure minimum system disruption enabling continuity of service to healthy

portion of the network.

When relays meant to protect specific equipments, transmission/distribution lines/feeders or

primary zone protective relays, do not operate and clear the fault in their primary protectionzone, backup relays located in the backup zone, must operate to isolate the fault, after providing

sufficient time discrimination for the operation of the primary zone relays.

The protective relays must also be able to discriminate between faulted conditions, normal

operating conditions and abnormal operating conditions and function only for the specificprotection for which they are designed, without operating for any normal and short term

acceptable abnormal events for which they are not intended to act and provide protection.

The term or phrase relay coordination therefore covers the concept of discrimination,

Selectivity and backup protection as explained in the foregoing discussion. Further thecoordination is not confined only to relays and equipment operating characteristics, but also
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includes other protective device characteristics such as Fuse, MCB's, Circuit Breakers as

applicable.

Relay coordination calculation module must consider the operating characteristics of the relays,normal operating and thermal or mechanical withstand characteristics of the equipments and

must determine the optimum relay settings to achieve the objectives stated to protect theequipments and to ensure continuity of power supply to healthy part of network.

Apart from the fault or short circuit conditions, protection system must also be designed toprovide protection against thermal-withstand limits, motor stalling, negative sequence current

with-stand limits, protection against abnormal frequencies, and protection against unbalance

operating conditions as applicable to various equipments and operating situations.

Frequency relay settings can be determined by using a dynamic simulation tool, such as transientstability analysis.Frequency Control Engineering;Transient Stability Analysis

Overcurrent Phase/Earth Fault Relays

Overcurrent phase fault relays.

Overcurrent earth fault relays.

High set relay settings to ensure protection against primary zone faults.

Coordination with maximum load current.

Coordination with fuse characteristics.

Coordination with maximum motor starting current and time.

Coordination with transformer inrush current.

Coordination with primary-back up pairs.

Coordination with thermal withstand capabilities ([I-square]t = K characteristics).

Coordination with safe stall limits for Motors.

Automatic generation of TCCs showing all relevant coordination.

Automatic identification of primary and back up relay pairs.

Provision for user defined back up relays for specific primary relays.

Solution for multiple island networks.

Multiple study cases for different network and source configurations in a single executionof the program.

Built in libraries of commercial relays, IEEE and IEC characteristics.
http://www.powerapps.org/PAES_FrequencyControlEngineering.aspxhttp://www.powerapps.org/PAES_FrequencyControlEngineering.aspxhttp://www.powerapps.org/PAES_TStability.aspxhttp://www.powerapps.org/PAES_TStability.aspxhttp://www.powerapps.org/PAES_FrequencyControlEngineering.aspxhttp://www.powerapps.org/PAES_TStability.aspx


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Distance Relay Settings

Zone setting calculations for zone 1 and 2.

Zone 3 setting calculations based on inbuilt short circuit calculations.

Settings for different commercially available relays.

Different relay characteristics MHO , Polygonal , Lens , Circle , R/X Blinder, Offset

characteristic.

R/X diagrams.

Solution for multiple islanded network in a single execution of the program.

Solution for multiple study cases with different network configurations in a single

execution of program.


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http://www.powerapps.org/PAES_TransformerProtection.aspx

http://www.powerapps.org/PAES_EquiProApps.aspx

http://www.powerapps.org/PAES_GeneratorProtection.aspx

http://www.powerapps.org/PAES_ShortCircuit.aspx

Transformer Protection

Although transformers are generally provided with both electrical and mechanical protection

schemes, our services are related to the protection against the electrical disturbances.The general electrical protection provided to a transformer are related to the following

-overload protection

-protection against short circuits (internal / external)

-protection against ground faults-transient over voltages (switching, lightning )

Protection against overload is achieved using overcurrent relays and details of thermal with standcapability curves of the transformer.Protection against external short circuit condition is achieved by fuses, overcurrent relays with

are without instantaneous settings. Protection against internal short circuit is achieved by proper

application of differential protection. Suitable differential protections are needed separately forphase and ground faults.

Protection against over voltages due to switching, lightning, switching of capacitor banks or

other system disturbances is achieved by proper insulation coordination.
http://www.powerapps.org/PAES_TransformerProtection.aspxhttp://www.powerapps.org/PAES_EquiProApps.aspxhttp://www.powerapps.org/PAES_GeneratorProtection.aspxhttp://www.powerapps.org/PAES_ShortCircuit.aspxhttp://www.powerapps.org/PAES_TransformerProtection.aspxhttp://www.powerapps.org/PAES_EquiProApps.aspxhttp://www.powerapps.org/PAES_GeneratorProtection.aspxhttp://www.powerapps.org/PAES_ShortCircuit.aspx


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Power System Equipment Protection

Applications and Studies

The complete protection system review of a system will be performed considering the following

criteria.

Accepted Engineering practices in protection. Applicable IEEE/IEC standards.

Information available in the application guides and relay catalogues of the relaymanufacturer. This criterion will be generally more used in determining relay settings in

comparison to the other methods specified for equipment protections.

IEEE Protection Standards

The following is the partial list of possible IEEE protection related standards that may be used by

the consultants in offering power system protection studies.

C37.106TM-2003, (Revision of ANSI/IEEE C37.106-1987), IEEE Guide for Abnormal

Frequency Protection for Power Generating Plants.

IEEE Std C37.101-1993, (Revision of IEEE Std C37.101-1985), IEEE Guide forGenerator Ground Protection.

ANSI/IEEE C37.97-1979, IEEE Guide for Protective Relay Applications to Power

System Buses.

IEEE Std C37.91-2000, (Revision of IEEE Std C37.91-1985), IEEE Guide for Protective

Relay Applications to Power Transformers.

ANSI/IEEE C37.109-1988, IEEE Guide for the Protection of Shunt Reactors.

IEEE Std C37.113-1999, IEEE Guide for Protective Relay Applications to Transmission

Lines.

IEEE Std C37.95-2002, (Revision of IEEE Std C37.95-1989), IEEE Guide forProtective Relaying of Utility-Consumer Interconnections.

IEEE Std C37.108-2002, (Revision of IEEE Std C37.108-1989), IEEE Guide for theProtection of Network Transformers.

IEEE Std C37.99-1980, IEEE Guide for Protection of Shunt Capacitor Banks.


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IEEE Std C37.96-2000 , (Revision of IEEE Std C37.96-1988), IEEE Guide for AC Motor

Protection.

IEEE Std 1410-1997, IEEE Guide for Improving the Lightning Performance of Electric

Power Overhead Distribution Lines.

IEEE Std 519-1992 (Revision of IEEE Std 519-1981), IEEE Recommended Practices andRequirements for Harmonic Control in Electrical Power Systems.

IEEE Std 399-1997, IEEE Recommended Practice for Industrial and Commercial Power

Systems Analysis.

IEEE Std 242-2001, American National Standard (ANSI), (Revision of IEEE Std 242-1986), IEEE Recommended Practice for Protection and Coordination of Industrial and

Commercial Power Systems.

IEEE Std 141-1993 (Revision of IEEE Std 141-1986) IEEE Recommended Practice for

Electric Power Distribution for Industrial Plants.

Generator ProtectionGenerator protection requires the consideration of many abnormal conditions that are not present

with other system elements. The abnormal conditions that may occur with generators include

1. Overheating

2. Stator (due to overload or loss of cooling)3. Rotor (due to overexcitation, loss of cooling , negative sequence stator currents)

4. Winding faults

5. Stator (phase and ground faults)6. Rotor (ground faults and shorted turns)

7. Overspeed and underspeed

8. Overvoltage9. Loss of excitation

10. Motoring

11. Unbalanced current operation12. Out of step

13. Subsynchronous oscillations

14. Inadvertent energization

15. Nonsynchronized connectionWe generally evaluate the protection settings based on relay application manuals provided by the

relay manufacturers and use variety of analytical tools and calculations where needed for further

investigations to assess the adequacy of protection and relay performance.


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Harmonic Measurements, Analysis and Filter

Design

Harmonics in power systems can result in undesirable influence such as Capacitor

heating/failure, Telephone interference, Rotating equipment heating, Relay misoperation,Transformer heating, Switchgear failure, Fuse blowing. The main sources of harmonics in power

system are static power converters, arc furnaces, discharge lighting and any other load that

requires non-sinusoidal current. In order to limit the harmonic current propagation in to the

network, harmonic filters are placed close to the source of the harmonic currents. Harmonicfilters provide low impedance paths to harmonic currents and thus prevent them from flowing

into the power network. Harmonic analysis program computes indices such as total voltage

harmonic distortion factor at system buses to evaluate the effect of the harmonic sources and toevaluate the effectiveness of the harmonic filters. Also, driving point impedance plots of the

buses of interest are generated to identify whether series or parallel resonance phenomenonoccurs at any harmonic frequency of interest.

Our Approach to Harmonic Analysis

We use 4 step approach as described in this section.

-In the first step for existing and functional networks harmonic current measurements is performed at

selected points to identify the harmonic currents injected into the network by the harmonic

sources. These measurements reflect harmonic currents for one operating configuration and theloads prevailing at the time of measurements only. These may not represent conservative

estimates of harmonic currents available.

-In the second step, the measurement information of the first step will be used along with design dataof harmonics where available from non-linear loads, generating harmonic currents. A computer

network model will be prepared as per IEEE standards and the effect of various harmonic sources

at various harmonic orders will be examined. Various harmonic distortion factors will be

computed as outlined in relevant IEEE standards. The advantage of computer model and

simulation is that it can take care of large number of operating configurations and conservative

estimates of harmonic currents, which cannot be covered by field measurements. Field

measurements of the first step, can however be used to validate the computer model developed.

- In the third step, harmonic driving point impedances of all buses of interest will be generated at

various harmonic orders and plots of the driving point impedances will be generated with respectto a range of harmonic orders [orders 1 through 50]. These plots indicate series and parallel

resonance conditions in network.

-In the fourth step, analysis of results of the first 3 steps will be carried out and solutions needed to

solve any harmonic related problems will be obtained. These solutions are verified by using the

computer model developed. The problems that might arise could be excessive harmonic distortion

factors beyond relevant IEEE specified standards, existence of resonance conditions close to an

exciting harmonic frequency. Where these problems are encountered, solutions will be provided


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by introduction of harmonic filters and its design will be verified again by using the computer

model developed. Recommendations include specifications on sizing of individual components of

the harmonic filters.

Our Guide Lines for Harmonic Measurements

1. Case 1: In this case the power supply to individual loads are supplied by dedicated

panels, with no other loads other than the specific non-linear load. The load size issignificantly large enough to warrant a specic dedicated harmonic filter. The

measurements will be taken for this load feeder

2. Case 2: A single supply switch board supplies several non-linear loads. All loads aresufficiently small and nearly similar to each other. In this case dedicated harmonic filters

for individual loads may not be necessary. A common filter may be provided at the

incomer, provided the outgoing feeder loads are reasonably constant. The measurement

will be done on the incomer of the switch board only.

3. Case 3: A single switch board supplies several non-linear loads. The nature of the loadsare significantly different from each other. The net switch board load is not constant oruniform making it difficult to arrive at a common filter at the incomer. In this case we

take harmonic measurements at each outgoing feeder and design individual load filters.

Apart from the above cases for harmonic measurements for purpose of filter design, it may be

necessary to carryout measurements at point of common power coupling at HV levels to ensurethat statutory requirements are satisfied.

From the guidelines provided, it is fairly straightforward to examine the electrical network and to

determine the number of measurement points. Measurements may have to be performed at

different short circuit levels at the point of grid coupling as the electrical network characteristicschanges with fault levels.

General Features of Harmonic Measurements, Filter Design

and Analysis

Distortion Factor Calculations as per IEEE 519 Standard.

Impedance Frequency Scans to identify parallel and series resonance points and bus

locations.

Modelling of harmonic sources and filters.

Modelling of all electric circuits as function of frequency.

Analysis using design data or Field measurements.

Analysis for various network configurations, fault levels.


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Simultaneous solution of multiple islanded network.

Single execution and report generation for multiple study cases.

Calculation of harmonic current flows in specified circuit elements.

Display of computed harmonic distortion factors, harmonic bus voltages, harmoniccurrents on single line diagram for all study cases.

Evaluation of adequacy of filter design.

Design of filters considering the harmonic currents to be filtered and reactive power

compensation needed at fundamental frequency.

Field measurements of power flows, harmonics and reports on the same.

Sample Single Line Diagram and Driving Point ImpedancePlot for Harmonic Analysis


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Switching Transient Study

These studies are generally performed to assess the transients associated with:

Energization of overhead transmission lines and study of associated transients, surgearrester ratings, transient mitigation methods.

Energization of capacitor banks / reactors in industrial or public utility facilities.

Transients associated with various switching actions such as fault application andclearance.

Motor Starting Studies

The starting current of most ac motors is several times normal full load current when starting

them directly on line at full rated voltage. The starting torque varies directly as the square of the

applied voltage. Excessive starting current results in drop in terminal voltage and may result inthe following:

Failure of motor starting due to low starting torques.

Unnecessary operation of under voltage relays.

Stalling of other running motors connected to the network.

Voltage dips at the power sources and consequent flicker in the lighting system.

Motor starting studies can help in the selection of best method of starting, the proper motordesign, and the proper system design for minimizing the impact of the motor starting.

Analysis of motor starting methods can be performed by both static and dynamic simulation

techniques as follows. These techniques have their own conveniences, advantages anddrawbacks. We believe mainly in transient (dynamic) motor starting studies that reproduce

observed (measured) motor starting conditions.

-Load flow type solution with the perceived starting impedance of the motor modeled as partof network modeling

-Short circuit method type of calculations considering pre-fault short circuit conditions and

using voltage drop calculations considering motor starting currents. Alternatively

-Where accurate dynamic model of the motor electric circuit and load torquecharacteristics are available, dynamic model of the motor can be used in traditional

transient stability algorithm to assess the impact of the motor starting.

-In the absence of accurate model information, transient stability studies can be used wherethe observed (measured) starting current can be used as nodal injection at the motor bus

as a dynamic event and the system response to this dynamic event can be evaluated.

The various methods described above can take into account all types of motor starting such as-Direct on line


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-With compensation

-Auto transformers

-Soft Starters-Start Delta Start

-Performance curves supplied from manufacturer

-Variable frequency drives

See: View Typical Plots of Motor Starting Studies(with assumed worst case load torque characteristic)

Evaluation of energy transaction in De-

regulated market - Energy Pricing, Wheelingand banking charges, Transmsission and

distribution Pricing, Grid Support services.

Energy Transactions in De-Regulated Market

The present deregulated market environment in India has separated the business functions relatedto transmission, generation and distribution. Consequently issues that were not present in the inthe past in managing and accounting above functions have surfaced with a plethora of problems

and approximate solutions. Some of the important issues are:

Transmission Pricing. How much a consumer must pay a transmission company for

utilizing its services?

Grid Support Charges. How much a consumer must pay to a transmission company or a

distribution company for merely providing grid support, so that plant can absorb

fluctuations in power supply and can get emergency support from the grid?

Wheeling and Banking Charges. What if a generation company wants to sell its excesscapacity to a consumer located somewhere in the grid network any where in India? Whatwill be the charges to be paid to the various transmission companies and distribution

companies whose facilities might have been used in such transaction?

What is the influence of transmission congestion on the pricing?

What about the pricing for the reactive power support?
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How do we monitor actual energy transactions between various stake holders? This is

essential to determine the actual finance charges to be paid from the user of the facilities

to the provider of services (facilities) according to an accepted and agreed norm. Thesemonitoring and associated computing methods are essential as the pricing may take into

consideration various factors as opposed to earlier simple energy transaction as the basis.

How do we know whether the tariff arrived at is based on correct calculations of an

accepted norm?

How do we know, whether a pricing norm is justifiable? Or needs revision due to certain

new factors that were not considered in the earlier norm?

Transmission facilities used by a consumer may have been used by other consumers as

well. How are the charges of transmission pricing to be shared among all users of thetransmission facilities?

Should the charges payable to new transmission facility and old transmission facilities be

same?

In a given power transaction between supplier (generation company) and a customer,

which are the transmission facilities that have been used? what is the extent of usage andhence, what are the charges to be paid?

Most of the factors indicated in this section need plain load flow analytical tool (load flow

studies) to provide solution at the present time based on accepted system data. Some of the

factors need continuous monitoring, recording and evaluation of energy transactions. Additionalinformation that may be needed are financial aspects of investment (capital cost), depreciation

charges, O&M charges and other establishment charges of a utility company.

The best and most justifiable pricing policy guidelines according to us are:

User of a transmission facility must pay for the portion of the facility used.

User of a transmission facility must pay for the extent of usage of the facility.

Earlier, transmission pricing was uniform without regard to above factors on usage.

It will be difficult to any consultant to address all the issues and to arrive at satisfactory solution

acceptable to all parties involved. Our experience is that no matter, how much we trust our

solutions and wisdom, there will always be a differing view from the other quarters. Wetherefore will act in the best interest of our clients on any issues raised by statutory regulatory

bodies by performing needed technical analysis based on available information. These technicalanalyses primarily use load flow solutions and other technical solutions may also be neededdepending on the issues that may arise. On any issues for which a client may need solution, we

will study the applicable central and state grid code, tariff orders, electricity acts and will provide

essential technical support to our clients.


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Energy Audit Services

Many utilities in India do not have adequate and reliable metering facilities for all their

consumers. Often this has resulted in erroneous estimations in the following:

Energy consumptions by un-metered facilities.

Transmission losses.

Distribution losses.

Growth in energy demand in different categories of consumers.

Energy theft.

In addition there is a need to identify erroneous meters and plug holes in revenues. To meet the

objectives stated it becomes necessary to provide comprehensive metering and analysis of the

metered data through efficient computerization. Computer analysis using technical analysis toolsand other suitable commercial analysis can indicate errors if any in metering, billing and other

aspects if any. This information can be used to take corrective and preventive actions by a utility

See: Services to Regulatory Commissions

Services to Electricity Regulatory

Commissions

The major role of electricity regulatory commissions in India covers the following issues

Tariff regulation of various generation, transmission and distribution licensees

Facilitation of open access among licensees

Adjudicate on disputes between among licensees and customers

Formulating operating guidelines for better reliability, quality of power supply, minimal

loss of power supply

Formulating Grid codes to be followed by licensees

Approving expansion plans of the licensees due to demand growth

As part of the role, the commission needs to perform many techno-commercial analysis such as
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o Energy demand growth estimate

o Estimation of losses

o Load flow studies

o Necessary support in grid code formulation

o Revenue sharing studies among licensees

o Revenue structuring

o Market monitoring

o Any other studies as needed

We provide necessary support to the commission in evaluating the specific issues using our deepknowledge in the electricity system design, operation, control and planning.

We also undertake development of custom software tools and provide them to electricityregulatory commissions along with the necessary training, documentation and technical support.

Long Term Energy Demand Forecast

(LTEDF)

Long term energy demand forecast is the preliminary step in planning future generation,

transmission and distribution facilities. It uses historical information of area wise, category wise

energy consumption and other correlated social and economic variables to project the energydemand requirement for the future years. The results of the long-term energy demand forecast, in

conjunction with the projection of the electricity tariffs, expenditures, investment history,

planned future additions required etc. can be used to perform suitable financial analysis toprovide information about the financial needs of an electric utility company. Future electrical

energy requirement projections provide basis for market analysis for different electrical

equipment manufacturers.

General Features of LTEDF

Trend Analysis. Linear, Quadratic, Exponential and Polynomial Trends.

Linear Multi-variable Regression Analysis.

End Use Methods.


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Partial End Use Methods.

Scenario Approaches.

In built statistical calculations to assess the accuracy of predictions.

Micro and Macro area predictions. Smoothening of micro area predictions based onMacro area predictions.

Predictions for energy related, socio-economic and finance related variables.

Graphic representation of trends as X-Y Plots, Bar Charts, Pie Charts.


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EMTP, Line Constants, Parameter

Evaluation, Insulation Coordination

EMTP and Line Constants (LC)

The features of EMTP and Line Constants Program given below are similar to a program

developed by M/s Microtran Power System Analysis Corporation, with the exception that

available software will not handle Power Electronics Circuits, ideal transformers and rotatingmachines. Details of EMTP and Line constant features, the technical documents, user documents

and a free student limited edition of the Microtran software can be down loaded from the website http://www.microtran.com.

General Features of EMTP and LC

Lumped R, L, C elements.

Multiphase pi-circuits.

Single and three-phase n-winding transformers.

Transposed and untransposed distributed parameter transmission lines with constant orfrequency dependent parameters.

Nonlinear resistances and surge arrester models (including metal oxide arresters), as well

as nonlinear inductances with user-defined residual flux.


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Switches with any number of opening/closing sequences, and other switching control

criteria to simulate circuit breakers with multiple closing- opening sequences, spark gaps,

etc.

Diodes, thyristors, and anti-parallel thyristor models with either fixed, or user-defined

firing controls.

Voltage and current sources. In addition to standard mathematical functions (sinusoids,

surge functions, steps, ramps), the user may specify sources point by point as functions oftime, or calculate them inside the user-supplied subroutine SOURCE.

Synchronous machines with armature, field, and damper windings. The model also

includes a shaft- mass system representation for the simulation of torsional oscillations.

Initial conditions can be determined automatically by the program or they can be supplied

by the user. The program can also be used to obtain steady-state phasor solutions at agiven frequency or over a user-defined frequency range. The "frequency scan" capability

is particularly useful for harmonics, resonance and subsynchronous resonance studies.

User-supplied linear or nonlinear models using the entry point routine CONNEC. The

procedure is quite simple: the user compiles his version of CONNEC with any compiler

capable of creating a DLL. A sample version of CONNEC and detailed interfaceinformation is available to would-be developers.

Insulation Coordination

Insulation Coordination is the process of determining the proper insulation levels of variouscomponents in a power system as well as their arrangements. It is the selection of an insulation
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structure that will withstand voltage stresses to which the system or equipment will be subjected

to, together with the proper surge arrester. The process is determined from the known

characteristics of voltage surges and the characteristics of surge arresters.

The following standards are used by the consultants, while performing the insulation

coordination:

Insulation Co-ordination, Part 1: Definitions, principles and rules IEC 71-1, standard. Insulation Co-ordination, Part 2: Application guide IEC 71-2, standard.

IEEE Guide for the Application of Insulation Coordination. IEEE Std 1313-2-1999.

Summary of Application of EMTP Studies*

EMTP is used world-wide for switching and lightning surge analysis, insulation coordination and

shaft torsional oscillation studies, protective relay modeling, harmonic and power quality studies,HVDC and FACTS modeling. Typical EMTP studies are:

Lightning overvoltage studies

Switching transients and faults

Statistical and systematic overvoltage studies

Very fast transients in GIS and groundings

Machine modeling

Transient stability, motor startup

Shaft torsional oscillations

Transformer and shunt reactor/capacitor switching

Ferroresonance

Power electronic applications

Circuit breaker duty (electric arc), current chopping

FACTS devices: STATCOM, SVC, UPFC, TCSC modeling

Harmonic analysis, network resonances

Protection device testing

* Source: ATP - EMTP User Manual.


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Insulation Coordination Studies for a 132 kVSubmarine Cable Interconnection

A Case Study Description Implemented in the Middle East Region

AbstractThe concept of insulation coordination is well known, however, the exact and detailed method performing these

studies are not practiced to the same extent as regular power system analysis and studies. A study case is presented in this

paper, where power frequency temporary over voltage, switching frequency and lightning over voltage studies [fast and

very fast front over voltage studies] are performed strictly in accordance with the IEC standards 60071 parts 1 and 2. The

power frequency over voltage studies were performed using standard power system analysis tools such as load flow, short

circuit and transient stability studies. The statistical switching and lightning over voltage studies were performed usingthe EMTP software. The details of the studies are presented in this paper.

Keywords-Insulation coordination, Power Frequency Overvoltage Studies, Switching Frequency Overvoltage studies,

Lightning overvoltage studies, Selection of withstand levels, Surge arrester applications.

Introduction


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The utility operating company in a middle east country region has been operating the offshore oilfield in island Ufor over 40 years. Over the years, various installations were upgraded / added to the existing complex consumingsignificant amount of spare power generation capacity. The facilities in the island U is now facing up-grades for new

process installation as the utility envisages various business opportunities in and around its facilities in the island.Consequently, the electrical local load growth demands additional power generation. Therefore, upgrades of theexisting power generating system are envisaged to meet these demands.

In relation to the above, the operating utility in the island U intends to meet the additional load demand at theisland, by means of providing a sub-sea cable link, of approximately 40 KMs, from D Island power system to the Uisland power system. In respect of this proposed tie-in various engineering studies, power system studies andinsulation coordination studies were performed. This paper outlines the insulation coordination studies performed and

presents the summary of the studies.

Description of the system

The islands of U and D both have gas turbine generators with the island D having the surplus generation. The 132kV sub-sea cable link is initially planned to operate at 33 kV level and later to be upgraded to 132 kV operatingvoltage level. The studies were performed considering that the initial operating voltage will be at 33 kV level. Thoughthe proposed sub-sea cable is adequately sized, the initial proposed operating conditions envisaged a maximum exportof about 8 MW power from the island D to U, which is lower than the cable capacity. The single line diagram of the

system considered for the analysis is shown in the figure 1.

Insulation Coordination Study

Insulation co-ordination procedure consists of the selection of the highest voltage for the equipment together witha corresponding set of standard rated withstand voltages which characterize the insulation of the equipment neededfor the application. The optimization of the selected set of withstand voltages Uw may require reconsideration ofsome input data and repetition of part of the procedure till satisfactory results are obtained.

The first step in the insulation coordination is the determination of the representative over voltages in the system[Urp] to which the electrical circuit is subjected to , under various operating conditions and switching phenomena.IEC standard 60071 classifies these over voltages as

a. Low frequency continuous over voltages. Power Frequency Load flow analysis used to determine these over

voltages.b. Low frequency temporary over voltages. These are determined by transient stability analysis and unbalanced

short circuit studies involving ground faults.

c. Transient slow front overvoltages. These are determined by statistical switching , line energization studieswith or without pre-insertion resistors or other means of over voltage control.


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d. Transient fast front switching overvoltages. These are determined by statistical switching studies, withunbalanced faults, fault removal, and switch reclose with or without fault removal on energized lines.

e. Transient very fast front lightning over voltages. These are determined from the lightning over voltagestudies.

Power Frequency Overvoltage Studies

The objective of load flow studies is to examine the power frequency over voltages in the system under allpossible operating conditions. These operating conditions involved no load cases or complete loss of load conditionsas well, to assess the extent of over voltages under no load conditions. A list of sample study cases considered forload flow, short circuit and Transient stability studies is as follows

1. Two generators of island U in operation along with all D island generators at Peak Load

2. All generators of both islands in operation at peak load, sharing loads

3. Two U generators in operation at peak load with loss connection between D island and U island.

4. Two U island generators in operation along with all D island generators at No Load

5. All D island generators along with two U island generators in operation with reduced output at PeakLoad such that there is maximum flow in Sub-Sea cable from island D to U

6. All U island generators in operation along with all D island generators except one gas turbine at peakLoad such that there is maximum flow in Sub-Sea cable from U to D

For each of the network configurations, the short circuit studies were also performed to compute the over voltageson healthy phases during ground fault conditions. Further transient stability studies were performed for the followingdisturbance scenarios and events

e 1: System SLD


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- 3 Phase faults and fault removal by isolating the faulted circuit , to determine the over voltages , their duration, upon fault removal.

- Loss of load conditions resulting in over voltages.

Switching Frequency, Fast Front, Very Fast Front

Overvoltages

Statistical switching studies were performed using the ATP-EMTP software for the following switching scenarioswith and without proposed surge arresters. These studies involved

a. Line Energization studies with receiving end open ended

b. Single phase fault, with single phase reclosing after fault clearance

c. Single phase fault, with single phase reclosing after unsuccessful fault clearance

d. Single phase fault, with 3 phase reclosing after fault clearance

e. Single phase fault, with 3 phase reclosing after unsuccessful fault clearance

f. 3 phase fault, with 3 phase reclosing after fault clearance

g. 3 phase fault, with 3 phase reclosing after unsuccessful fault clearance

Apart from the above lightning over voltage studies of a typical 33 kV overhead line was also considered for theinsulation coordination calculations to arrive at the conservative values , as the lightning was not applicable for thesub-sea cable system.

Modeling of Sub-sea cable for EMTP studies

In electromagnetic transient simulations there are basically two ways to represent transmission

lines/cables:

i. Lumped parameter models: Nominal and exact PI-models

ii. Distributed parameter models/traveling wave models: Bergeron and frequency-dependent models

Nominal PI-model: The nominal PI-model is one of the simplest representations that can be done of a

cable line. It includes the cable's total inductance, capacitance, resistance and conductance (usually not

considered) modeled as lumped parameters.

Exact PI-model: The exact PI-model, sometimes also called the equivalent pi-model, is a more advanced

version of the nominal pi-model that considers the distributed nature of the impedance and admittance.

This model is accurate when used in the frequency domain for a single frequency and is normally used to

validate other models.

Bergeron model: The Bergeron model is a constant-frequency model based on traveling wave theory. The

cable is considered to be lossless and its distributed resistance is added as a series lumped resistance.

Typically, the model is divided into two sections, it can be divided in more sections, but the differences in

the results are minor. This model is a constant-frequency model and its use is only recommended for the

cases when only one frequency is considered.


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Frequency Dependent (FD) models: As the name indicates, FD-models are models that have frequency-

dependent cable parameters. When compared with the previous models, the use of the frequency domain

increases the results accuracy. In FD-models all calculations are performed in the frequency domain and

the solutions converted to time domain by the using transformations such as Fourier-transform or Z-

transform.

For this study Exact PI model was considered.

Sample Simulation Results and Plots

Conclusions/Recommendations

The lightning, switching overvoltage and insulation co-ordination studies were carried out for the 33kV sub-seacable system. The model representing the 33kV system is carried out as recommended in IEC 60071-2, and inaccordance with the next extend as required by EMTP. All studies were based on the relevant international standard,i.e. IEC 60071-2.

e 2: Voltage profile at one end of the Sub-Sea cable [without Surge

Arrester]

e 3: Voltage profile at one end of the Sub-Sea cable [with Surge

Arrester]


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REFERENCESIEC 60071-2, "Insulation Co-ordination - Part 2: Application guide", 1996

IEC TR 60071-4, "Insulation Co-ordination - Part 4: Computational guide of insulation co-ordination and modeling of electrical networks, 2004

IEC 60099-4, Surge arresters Part 4: Metal-oxide surge arresters without gaps for A.C. systems

Power QualityTo us Power Quality is characterized by

1. Stable AC voltages at near nominal values and at near rated frequency subject to

acceptable minor variations, free from annoying voltage flicker, voltage sags, frequencyfluctuations.

2. Near sinusoidal current and voltage wave forms free from higher order harmonics

All electrical equipments are rated to operate at near rated voltage and rated frequency. Hencethe first point is one of the criteria of for assessing the power quality.

As indicated in http://www.powerapps.org/Harmonic Measurements, Analysis and Filter

Design.aspx , harmonics in power supply can result in the following-Capacitor heating/failure

-Telephone interference

-Rotating equipment heating-Relay misoperation

-Transformer heating

-Switchgear failure

-Fuse blowingTo address the issues of power quality - we undertake detailed field measurements, monitor

electrical parameters at various PCCs, feeders to assess the operating conditions in terms of

power quality. If problems are found, we perform detailed studies using a computer model. The

accuracy of computer model is first built to the degree where the observed simulation valuesmatches with those of the field measurement values. This provides us with a reliable computer

model using which we workout remedial measures. For the purpose of the analysis we may useload flow studies, dynamic simulations, EMTP simulations, harmonic analysis depending on the

objectives of the studies.

We also evaluate the effectiveness of harmonic filters through the computer model built, paying

due attention to any reactive power compensation that these filters may provide at fundamentalfrequency for normal system operating conditions. Additionally the equipment ratings will also

be addressed to account for harmonic current flows and consequent over heating.

A related link on the studies is Harmonic Measurements, Analysis and Filter Design

Voltage Flicker Analysis and Solution
http://www.powerapps.org/Harmonic%20Measurements,%20Analysis%20and%20Filter%20Design.aspxhttp://www.powerapps.org/Harmonic%20Measurements,%20Analysis%20and%20Filter%20Design.aspxhttp://www.powerapps.org/Harmonic%20Measurements,%20Analysis%20and%20Filter%20Design.aspxhttp://www.powerapps.org/Harmonic%20Measurements,%20Analysis%20and%20Filter%20Design.aspx


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The voltage flicker is a phenomenon of unstable voltage resulting in poor performance of the

lighting and other voltage sensitive loads. The voltage flicker occurs as result of randomly

changing reactive power demand of the random process loads. Examples of such loads are

1. Electric arc furnace loads

2. Rolling mill loads

3. Large induction motor starting with long starting time

4. Large synchronous motors started as induction motors

5. Unbalanced and fluctuating loads

Typical solution involve providing necessary reactive power support as close to the loads

causing the flicker, and thus preventing the rest of network experiencing from voltage flicker

phenomenon. The reactive support system, will need to measure the reactive power demand fromthe loads and initiate a control to provide necessary reactive power support. Static Var

Compensators , STATCOMs, and even simple fixed capacitors [where fluctuation is temporary]are some of the devices used to achieve desired reactive power support and mitigation of thevoltage flicker phenomenon.

We provide simulation based recommendation on the sizing and type of reactive power

compensation based on the load profile as function of time. The simulation will use both static

load flow solutions and dynamic time domain simulations and capture the impact of therandomly varying loads on other system loads, flows, voltages. The various options for the

solution to mitigate the flicker problem will be evaluated through simulation and

recommendations will be provided on sizing, location and type of reactive power support neededto mitigate the voltage flicker problems.

Power Evacuation Studies

The phrase Power Evacuation Studies is a generic term associated with plans for evacuatingpower generated from a generating source to a load centre. In the simplest form, it may mean

only load flow studies with proposed transmission and distribution plans. When complete

engineering is involved, the entire spectrum of power system analysis/studies may have to be

performed.

Power Evacuation Studies may mean, studies related to new generation facility and its

connectivity to the grid for evacuation of the power or may mean studies related to existing

facilities to study alternative plans of power evacuation for operational purposes.

The objective of the studies is usually the checking feasibility of the various technical andeconomic aspects and therefore may encompass various other studies as follows.


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Load Flow or Power Flow Studies using standard load flow analysis techniques.

Static and Dynamic Contingency studies, using load flow analysis, transient stability

analysis, small signal stability analysis, voltage stability analysis techniques. This is doneto check the adequacy of the evacuation design or plan to withstand credible

contingencies and to assess the reliability aspects of power evacuation.

Reactive Power Compensation Studies for capacitor locations, sizing, optimum settings

for generator excitations, transformer taps. These studies are carried out using reactive

power optimization techniques based typically on linear programming methods. Theobjective is to ensure that power is supplied to load centers at acceptable voltage levels

and with minimum transmission losses.

Optimal Power Flow Studies. For economic dispatch or other suitable objectives. Theother suitable objective may contain, scheduled power exchange, removal of operational

infeasibilities, improving stability margin.

Engineering studies, such as site survey, plant and equipment locations, various

engineering plans and specifications [civil, structural, mechanical, instrumentation,piping, electrical etc], transmission routes, substation layout, circuit breaker sizing,ground mat design, insulation coordination, protection and coordination to complete the

designed Power Evacuation arrangement.

Switch Yard and Substation Design

We cover the following aspects of electrical engineering with respect to switch yard andsubstation design

Detailed single line diagrams

Electrical layout drawings

Busbar design

Breaker, isolator, switching arrangements, disconnector and earthing switches, sizingcalculations, specifications

Substation automation design, PLCC system design and implementation

Instrument transformers. CTs and PTs selection and specifications

Lightning (surge) Arrester specifications
http://www.powerapps.org/PAES_RPowerO.aspxhttp://www.powerapps.org/PAES_RPowerO.aspx


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Neutral grounding resistors calculations and specifications

Shunt reactor, series reactor, shunt capacitor requirements depending on reactive power

control needed, power transmission requirements, short circuit current limitation

requirements

Power transformer, distribution transformer, sizing, tap range requirement calculationsand specifications

Earthing and ground mat design

Lighting calculations and related specifications

Insulation coordination studies

Power cable selection, routing, schedules

Auxiliary standby power design

power system studies

Documents