basics of hvdc

V G RAOV G RAO

HVDC / KOLARHVDC / KOLAR

Due to ease of transformation of voltage levels (simple transformer action) and rugged squirrel cage motors, ALTERNATING CURRENT is universally utilised.—Both for GENERATION and LOADS and hence for TRANSMISSION.

Generators are at remote places, away from the populated areas i.e. the load centers

They are either PIT HEAD THERMAL or HYDEL

Turbines drive synchronous generators giving an output at 15-25 kV.

Voltage is boosted up to 220 or 400 KV by step-up transformers for transmission to LOADS.

To reach the loads at homes/industry at required safe levels, transformers step down voltage.

REASONS FOR AC GENERATION AND TRANSMISSIONREASONS FOR AC GENERATION AND TRANSMISSION

– CONVENTIONALLY POWER TRANSMISSION IS EFFECTED

THROUGH HVAC SYSTEMS ALL OVER THE WORLD.

– HVAC TRANSMISSION IS HAVING SEVER LIMITATIONS LIKE LINE

LENGTH , UNCONTROLLED POWER FLOW, OVER/LOW

VOLTAGES DURING LIGHTLY / OVER LOADED

CONDITIONS,STABILITY PROBLEMS,FAULT ISOLATION ETC

– CONSIDERING THE DISADVANTAGES OF HVAC SYSTEM AND THE

ADVANTAGES OF HVDC TRANSMISSION , POWERGRID HAS

CHOOSEN HVDC TRANSMISSION FOR TRANSFERRING 2000 MW

FROM ER TO SR

COMPARISION OF HVAC & HVDC SYSTEMS

HVDC: USE less currentHVDC: USE less current

• Direct current : Roll along the line ; opposing force friction (electrical resistance )

• AC current will struggle against inertia in the line (100times/sec)-cuurent inertia –inductance-reactive power

Better Voltage utilisation ratingBetter Voltage utilisation rating

DC has Greater ReachDC has Greater Reach

• Distance as well as amount of POWER determine the choice of DC over AC

DC DC

• The alternating current in a cable ”leaks” current (chargingmovements) in the same manner as a pulsating pressure

would be evened out in an elastic tube.

DIRECT CURRENT CONSERVES FORESTDIRECT CURRENT CONSERVES FORESTAND SAVES LANDAND SAVES LAND

• Fewer support TOWER, less losses

CONTROLLING or BEING CONTROLLING or BEING CONTROLLEDCONTROLLED

• By raising the level in tank ;controlled water flow

CONTROLLING or BEING CONTROLLING or BEING CONTROLLEDCONTROLLED

• ZERO IF Vr=VI=10V

HVDC leads to Better Use of AC HVDC leads to Better Use of AC TRANS SYS.TRANS SYS.

• FORCE HAS TO BE APPLIED IN RIGHT POSITION

HVDC provides increase power HVDC provides increase power but does not increase the short but does not increase the short

circuit POWERcircuit POWER

HVDC LEADS TO BETTER HVDC LEADS TO BETTER USE OF ACUSE OF AC

• HVDC and HVAC SHOULD CO-OPERATE FOR OPTIMUM EFFICIENCY

HVDC LEADS TO BETTER HVDC LEADS TO BETTER USE OF ACUSE OF AC

• If two networks are connected by an AC link, it can be in-efficient

ADVANTAGES OF HVDC OVER HVAC TRANSMISSION

– CONTROLLED POWER FLOW IS POSSIBLE

VERY PRECISELY

– ASYNCHRONOUS OPERATION POSSIBLE

BETWEEN REGIONS HAVING DIFFERENT

ELECTRICAL PARAMETERS

– NO RESTRICTION ON LINE LENGTH AS NO

REACTANCE IN DC LINES


– STABILISING HVAC SYSTEMS -DAMPENING OF POWER

SWINGS AND SUB SYNCHRONOUS FREQUENCIES OF

GENERATOR.

– FAULTS IN ONE AC SYSTEMS WILL NOT EFFECT THE OTHER

AC SYSTEM.

– CABLE TRANSMISSION

.


CHEAPER THAN HVAC SYSTEM DUE TO LESS TRANSMISSION

LINES & LESS RIGHT OF WAY FOR THE SAME AMOUNT OF

POWER TRANSMISSION

COST: AC vs DC TransmissionCOST: AC vs DC Transmission

Terminal Cost AC

Terminal Cost DC

Line Cost DC

Line Cost AC

Break Even Distance

HVDC BIPOLAR TRANSMISSION SYSTEM

2 DOUBLE CIRCUIT HVAC TRANSMISSION SYSTEMS

2000 MW HVDC VIS- A- VIS – HVAC SYSTEMS

Types of HVDC Types of HVDC

HVDC is the unique solution to interconnect asynchronous systems or grids with different frequencies.Solution: HVDC Back-to-Back

Up to 600 MW

Back-to-Back Station

AC AC

50 Hz 60 Hz

Types of HVDC Types of HVDC HVDC represents the most economical solution to transmit electrical energy over distances greater than approx. 600 km Solution: HVDC Long Distance

Up to 3000 MW

Long Distance Transmission

AC AC

DC line

Types of HVDCTypes of HVDCHVDC is an alternative for submarine transmission.Economical even for shorter distances such as a few 10km/milesSolution: HVDC Cable

Up to 600 MW

Long Submarine Transmission

AC AC

DC cable

HVDC BIPOLAR LINKS IN INDIAHVDC BIPOLAR LINKS IN INDIA

NER

ER

SR

NR

NER

ER

SR

NR

RIHAND-DELHI -- 2*750 MW

CHANDRAPUR-PADGE – 2* 750 MW

TALCHER-KOLAR – 2*1000 MWER TO SR

SILERU-BARASORE - 100 MW EXPERIMENTAL PROJECT ER –SR

HVDC IN INDIAHVDC IN INDIABipolarBipolar

HVDC LINK CONNECTING REGION

CAPACITY (MW)

LINE LENGTH

Rihand – Dadri

North-North 1500 815

Chandrapur - Padghe

West - West 1500 752

Talcher – Kolar

East – South 2500 1367

ASYNCHRONOUS LINKS IN INDIAASYNCHRONOUS LINKS IN INDIA

NER

ER

SR

NR

NER

ER

SR

NR

VINDYACHAL (N-W) – 2*250 MW CHANDRAPUR (W-S)– 2*500 MW

VIZAG (E-S) - 2*500 MW SASARAM (E-N) - 1*500 MW

HVDC IN INDIAHVDC IN INDIABack-to-BackBack-to-Back

HVDC LINK CONNECTING REGION

CAPACITY (MW)

Vindyachal North – West 2 x 250

Chandrapur West – South 2 x 500

Vizag – I East – South 500

Sasaram East – North 500

Vizag – II East – South 500

BASIC PRINCIPLES BASIC PRINCIPLES

OF

HVDC TRANSMISSION

AC Transmission PrincipleAC Transmission Principle

HVDC Transmission PrincipleHVDC Transmission Principle

Direct current is put to use in common life for driving our portable devices, UPSs, battery systems and vastly in railway locomotives.

USE OF DCUSE OF DC

DC AS A MEANS OF TRANSMISSIONDC AS A MEANS OF TRANSMISSION

This has been possible with advent of

High power/ high current capability thyristors

&

Fast acting computerised controls

Important Milestones in the Development of HVDC Important Milestones in the Development of HVDC technologytechnology

• · Hewitt´s mercury-vapour rectifier, which appeared in 1901.• · Experiments with thyratrons in America and mercury arc valves in

Europe before 1940.• · First commercial HVDC transmission, Gotland 1 in Sweden in

1954.• · First solid state semiconductor valves in 1970.• · First microcomputer based control equipment for HVDC in 1979.• · Highest DC transmission voltage (+/- 600 kV) in Itaipú, Brazil,

1984.• · First active DC filters for outstanding filtering performance in 1994.• · First Capacitor Commutated Converter (CCC) in Argentina-Brazil

interconnection, 1998• · First Voltage Source Converter for transmission in Gotland,

Sweden ,1999

High Voltage Thyristor Valve History Highlights

1967 First Test Valve: 2 parallel 35 mm Thyristors @ 1650 V

1969 World's First Contract for an HVDC System with Thyristor Valves

2 parallel 35 mm thyristors @ 1650 V for 2000 A

1975 World's First Contract for Watercooled HVDC Thyristor Valves

2 parallel 52 mm thyristors @ 3500 V for 2000 A

1980 World's First Contract for HVDC System with 100 mm Thyristors

no parallel thyristors @ 4200 V for 3600 A

1994 First HVDC Contract Using 8kV Thyristors

100 mm thyristors @ 8000 V

1997 First Thyristor Valve with Direct-Light-Triggering

100 mm thyristors with breakover protection @ 8000 V for 2000 A

2001 First complete HVDC System using Direct-Light-Triggered Thyristors with integrated breakover protection @ 8000 V

The Evolution of Thyristor Valves in HVDCThe Evolution of Thyristor Valves in HVDC

If DC is required to be used for transmission

&

since our primary source of power is A.C,

the following are the basic steps:

1. CONVERT AC into DC (rectifier)

2. TRANSMIT DC

3. CONVERT DC into AC ( inverter)

Purpose & function of Thyristor ValvePurpose & function of Thyristor Valve

• Connects AC phases to DC system

• Conduct High Current – currents upto 3000A without the requirement of paralleling of thyristors

• Block High Voltage – Blocks high voltage in forward and reverse direction up to 8KV

• Controllable – thyristor triggering /conduction possible with the gate firing circuits

• Fault tolerant and robust

SINGLE PHASE HALF WAVE RECTIFIERSINGLE PHASE HALF WAVE RECTIFIER

SINGLE PHASE SINGLE PHASE FULL WAVE FULL WAVE RECTIFIERRECTIFIER

SINGLE PHASE FULL WAVE BRIDGE RECTIFIERSINGLE PHASE FULL WAVE BRIDGE RECTIFIER

6-Pulse Convertor Bridge6-Pulse Convertor Bridge

3

6

CiLs

4

E1 Ls

Ls

Bi

iA

1

2

I

V'd

5

Vd

IddL

d

Voltage and Current of an Ideal Voltage and Current of an Ideal Diode 6 Pulse ConverterDiode 6 Pulse Converter

Alpha = 0

Overlap = 0

Operation of ConverterOperation of Converter

• Each thyristor conducts for 120º

• Every 60º one Thyristor from +ve limb and one Thyristor from –ve limb is triggered

• Each thyristor will be triggered when voltage across it becomes positive

• Thyristor commutates the current automatically when the voltage across it becomes –ve. Hence, this process is called natural commutation and the converters are called Line Commutated converters

• Triggering can be delayed from this point and this is called firing angle α

• Output voltage of the converter is controlled by controlling the α – Rectifier action

• If α > 90º negative voltage is available across the bridge – Inverter action

• Due to finite transformer inductance, current transfer from one thyristor valve to the other cannot take place instantly

• This delay is called over lap angle μ and the reactance called commutating reactance. This also causes additional drop in the voltage

Operation of ConverterOperation of Converter

Ideal No-Load ConditionIdeal No-Load Condition

B

2

A

1

C

3

Vd

Effect of Control AngleEffect of Control Angle

B

A

2

C

1

u u

Vd

u

3

RECTIFIER VOLTAGERECTIFIER VOLTAGE

INVERTER VOLTAGEINVERTER VOLTAGE

DC Terminal VoltageDC Terminal Voltage

120 º

RECTIFICATION

0240 º180 º 300 º 120 º60 º 180 º

0.866E . 2 LLE . 2 LL

DC Terminal VoltageDC Terminal Voltage

120 º

INVERSION

0240 º180 º 300 º 120 º60 º 180 º

0.866E . 2 LLE . 2 LL

DC Voltage Verses Firing AngleDC Voltage Verses Firing Angle

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 30 60 90 120 150 180

Vd

alpha

Vd=Vac*1.35 *(cos alpha-uk/2)

Valve Voltage and Valve CurrentValve Voltage and Valve Current

120 180A

u0.866

240120

u

60

FC

DB E

180A

u

60 60

K

G J L

HN

M

3000

Pu

S

E . 2 LL

60R

Q

RECTIFICATION =15º

+u

E . 2 LL

Valve Voltage and Valve CurrentValve Voltage and Valve Current

M Q

120 º 180 ºR

N

Pu

240 º120ºR

Q

180 º

u

0B

F

SA

C

ED

H

60 º

J

K

G L

INVERSION=15º

60º60º

u u

60º

0.866E . 2 LL

E . 2 LL


Y

Commonly Used in HVDC systemsCommonly Used in HVDC systems

• Commonly adopted in all HVDC applications• Two 6 pulse bridges connected in series• 30º phase shift between Star and Delta

windings of the converter transformer • Due to this phase shift, 5th and 7th harmonics

are reduced and filtering higher order harmonics is easier

• Higher pulse number than 12 is not economical


DC VOLTAGE AT DC VOLTAGE AT αα = 15º = 15º

HVDC Link Voltage ProfileHVDC Link Voltage Profile

I R

DC CABLE or O/H LINE

I Ed rd

RECTIFIER

dio RV

I X2

d c

cos

rI Ed

L I X 2d c

cos

Vdio I

INVERTER

VdR=VdioR cos-Id Xc+Er VdI=VdioI(cos-Id Xc+Er

2 2

Control of DC VoltageControl of DC Voltage

V 1 V 3 V 5

V 2V 6V 4

P hase A

UdP hase B

P hase C

Id

Pow er FlowAC System DC System

V 1 V 3 V 5

V 2V 6V 4

P hase A

UdP hase B

P hase C

Id

AC System DC SystemPow er Flow

30 60 90 120 150 1800

+Ud

-Ud

160

5

RectifierOperation

InverterOperation

Rectifier Operation Inverter Operation

Relationship of DC Voltage Ud and Firing Relationship of DC Voltage Ud and Firing Angle Angle αα

30 60 90 120 150 1800

+Ud

-Ud

160

L im it In v

5

L im it R e c t. RectifierOperation

InverterOperation

tw

o60=

Ud

o30=o0=

o90= o120= o150=

-Ud

tw

Ud

Ud

How does HVDC Operate?

NORMAL POWER DIRECTIONNORMAL POWER DIRECTION

REVERSE POWER OPERATIONREVERSE POWER OPERATION

Schematic of HVDCSchematic of HVDC

Modes of OperationModes of Operation

DC OH Line

Converter Transformer

ThyristorValves

400 kV AC Bus

AC Filters,Reactors

Smoothing Reactor


ThyristorValves

400 kV AC Bus

AC Filters, shunt capacitors

Smoothing Reactor

Bipolar

Current

Current


DC OH Line


ThyristorValves

400 kV AC Bus

AC Filters,Reactors

Smoothing Reactor


ThyristorValves

400 kV AC Bus

AC Filters

Smoothing Reactor

Monopolar Ground Return

Current


DC OH Line


ThyristorValves

400 kV AC Bus

AC Filters,Reactors

Smoothing Reactor


ThyristorValves

400 kV AC Bus

AC Filters

Smoothing Reactor

Monopolar Metallic Return

Current

Kolar

Chintamani

Cudappah

HoodyHosur

Salem

Udumalpet

Madras B’lore

+/- 500 KV DC line 1370 KM

ElectrodeStation

ElectrodeStation

TALCHER

400kv System

220kv system

KOLAR

TALCHER KOLAR TALCHER KOLAR SCHEMATICSCHEMATIC

Sharing of Talcher PowerSharing of Talcher Power

• Tamil Nadu - 636 MW•

• A.P. - 499 MW• • Karnataka - 466 MW

• Kerala - 330 MW

• Pondicherry - 69 MW

32%

23%

17% 3%

25%

T.N. A.P.

Karnataka Kerala

Pondy

KOLAR SINGLE LINE DIAGRAMKOLAR SINGLE LINE DIAGRAM

• Project Highlights

– FOR TRANSMITTING 2000 MW OF POWER FROM NTPC TALCHER

STPS -II AND FOR SHARING AMOGEST SOUTHERN STATES THE

2000 MW HVDC BIPOLAR TRANSMISSION SYSTEM IS

ENVISAGED AS

EAST SOUTH INTERCONNECTOR II (ESICON –II).

– THIS IS THE LARGEST TRANSMISSION SYSTEM TAKEN UP IN

THE COUNTRY SO FAR

– THE PROJECT SCHEDULE IS QUITE CHALLENGING

• AGAINST THE 50 MONTHS FOR SUCH PROJECTS, THE

PROJECT SCHEDULE IS ONLY 39 MONTHS

• SCHEDULED COMPLETION BY JUNE 2003

TACLHER-KOLAR ± 500 kV HVDC TRANSMISSION SYTEM

• Project Highlights

– KEY DATES

• AWARD OF HVDC TERMINAL STATION PKG - 14TH

MAR 2000

• AWARD OF HVAC PACKAGE - 27TH

APR 2000

– APPROVED PROJECT COST - RS. 3865.61 CR

– THIS IS THE FIRST OF SUCH SYSTEM WHERE THE ENTIRE

GENERATION IN ONE REGION IS EARMARKED TO ANOTHER

REGION.

Salient Features• Rectifier Talcher, Orissa

• Inverter Kolar, Karnataka

• Distance 1370 km

• Rated Power 2000 MW

• Operating Voltage 500 kV DC

• Reduced Voltage 400 kV DC

• Overload

• Long time, 40C 1.25 pu per pole

• Half an hour 1.3 pu per pole

• Five Seconds 1.47 pu per pole

SYSTEM CAPACITIES SYSTEM CAPACITIES

BIPOLAR MODE OF OPERATION -- 2000 MW

MONO POLAR WITH GROUND RETURN --- 1000 MW

MONO POLAR WITH METALLIC RETURN MODE --- 1000 MW

DEBLOCKS EACH POLE AT P min 100 MW

POWER DEMAND AT DESIRED LEVEL

POWER RAMP RATE -- 1 – 300 MW /MIN

POWER REVERSAL IN OFF MODE

SYSTEM CAPACITIESSYSTEM CAPACITIES

OVER LOAD CAPACBILITIES

RATED POWER -- 2000 MW

LONG TIME OVER LOAD POWER – 8/10 HOURS -- 2500 MW SHORT TIME OVER LOAD – 5 SEC- 3210 MW

HARMONIC FILTERS

AT TALCHER TOTAL FILTERS – 14 DT 12/24 FILTERS EACH 120 MVAR - 7 NOS DT 3/36 FILTERS EACH 97 MVAR - 4 NOS SHUNT REACTORS 138 MVAR- 2 NOSSHUNT CAPCITORS 138 MVAR- 1 NOSDC FILTERS DT 12/24 & DT 12/36 – 1 No per pole.

AT KOLAR TOTAL FILTERS – 17 DT 12/24 FILTERS EACH 120 MVAR - 8 NOS DT 3/36 FILTERS EACH 97 MVAR - 4 NOS SHUNT CAPCITORS 138 MVAR- 5 NOS DC FILTERS DT 12/24 & DT 12/36 – 1 each pole

– MONOPOLAR GROUND RETURN - 1000 MW POWER CAN BE TRANSMITTED THROUGH THIS MODE WHERE THE RETURN PATH IS THROUGH THE GROUND WHICH IS FACILITATED THROUGH A EARTH ELECTRODE STATION SITUATED AT ABOUT 35 KMS FROM THE TERMINALS AND CONNECTED BY A DOUBLE CIRCUIT TRANSMISSION LINE.

– MONOPOLAR METALLIC RETURN - 1000 MW POWER CAN BE TRANSMITTED THROUGH THIS MODE WHERE THE RETURN PATH IS THE TRANSMISSION LINES OF OTHER POLE.

– BALANCED BIPOLAR MODE – 2000 MW CAN BE

TRANSMITTED THROUGH THIS MODE WHERE WITH ONE +VE AND OTHER – VE .

SYSTEM CAPACITIESSYSTEM CAPACITIES

TALCHER-KOLAR HVDC & EHVAC SYSTEM

basics of hvdc

Documents