Slide: 1

Recent Developments in Electric PowerRecent Developments in Electric PowerTransmission TechnologyTransmission Technology

Dr.Dr. Kalyan Kalyan Sen Sen

April 15, 2003April 15, 2003

Slide: 2

S o u rc e L o a d

L o a d

■■ Demand for electricalDemand for electricalenergy is increasing.energy is increasing.

■■ “Free Flow” makes“Free Flow” makesparticular transmission linesparticular transmission linesoverloaded.overloaded.

■■ Construction of newConstruction of newtransmission lines hastransmission lines hasbecome increasingly difficultbecome increasingly difficultand expensive.and expensive.

■■ Energy needs to beEnergy needs to betransported from thetransported from thegenerating point to the end-generating point to the end-user along the mostuser along the mostdesirable path.desirable path.

Issues Facing Power Industry TodayIssues Facing Power Industry Today

Slide: 3

Issues Facing Power Industry TodayIssues Facing Power Industry Today■■ Voltage level may need to be restored at a point alongVoltage level may need to be restored at a point along

the line.the line.

V

IIds

s

sV

Vs δ

sVIqs

P ,s Qs

I

II

δdr

I90

2m1

VX

XL

V V

Vr Iqr

οοοο

VX

rP , Qr

I

Vr

V rr δ

Slide: 4

■■ Power flow in aPower flow in atransmission linetransmission linedepends ondepends on–– impedanceimpedance–– voltagevoltage–– phase angle.phase angle.

■■ Leading voltageLeading voltagesends activesends activepower to thepower to thelagging voltage.lagging voltage.

Principles of Power Flow in a Transmission LinePrinciples of Power Flow in a Transmission Line

XQr V

r

s

V

L

XV

sr

ss V

=

=PV

X

- )

r

r

L

V (cos δδδδ

Vsin δδδδ

XL

Vr

VI

QrP , r

(a) (b)

δδδδVs

90οοοο

VX

VI r

Slide: 5

Available SolutionsAvailable Solutions■■ Traditional TechnologyTraditional Technology

–– Voltage-Regulating TransformerVoltage-Regulating Transformer–– Shunt Inductor/CapacitorShunt Inductor/Capacitor–– Series Inductor/CapacitorSeries Inductor/Capacitor–– Phase Angle RegulatorPhase Angle Regulator

■■ Voltage-Voltage-SourcedSourced Converter Based Technology Converter Based Technology–– STATic synchronous COMpensator (STATCOM)STATic synchronous COMpensator (STATCOM)–– Static Synchronous Series Compensator (SSSC)Static Synchronous Series Compensator (SSSC)–– Unified Power Flow Controller (UPFC)Unified Power Flow Controller (UPFC)

Slide: 6

■■ Regulates the lineRegulates the linevoltage in smallvoltage in smallsteps by adding orsteps by adding orsubtracting asubtracting acompensatngcompensatngvoltage in seriesvoltage in serieswith thewith thetransmission line.transmission line.

Voltage-Regulating TransformerVoltage-Regulating Transformer

(c)Controller

s

*Vs'

v

VOLTAGEREGULATINGUNIT

MagnitudeCalculator

VsB

Vs

V

(a) Vs'B

sC

s'C V

EXCITER UNIT

Vs'A

Vs'B (b)V

TapControl

UnitTaps

s'sB

s'C

VsA

V

sBV

s'sC V

sCV

VsA V

s'AV

s'sA

Slide: 7

■■ Produces a variableProduces a variablevoltage.voltage.

Voltage-Regulating TransformerVoltage-Regulating Transformer

Controller

B

GateFiringCircuit

GateFiringCircuit

GateFiringCircuit

A

GateFiringCircuit

Slide: 8

■■ Regulates theRegulates theline voltage byline voltage byconnecting anconnecting aninductor or ainductor or acapacitor incapacitor inparallel with theparallel with thetransmission line.transmission line.

ThyristorThyristor-Controlled Static -Controlled Static Var CompensatorVar Compensator

Controller

CapacitorBanks

GateFiringCircuit

GateFiringCircuit

ReactorBanks

GateFiringCircuit

GateFiringCircuit

Step DownTransformer

Transmission Line

Slide: 9

Voltage and Current of a Voltage and Current of a ThyristorThyristor--Controlled ReactorControlled Reactor

TCR currentBus voltage

TCR

19 0 20 0 21 0 22 0 2 30 24 0

time25 0

x 10 -3

Slide: 10

■■ Regulates the lineRegulates the linevoltage by injectingvoltage by injectinga shunt reactivea shunt reactivecurrent into thecurrent into thetransmission line.transmission line.

STATicSTATic synchronous synchronous COMpensatorCOMpensator-STATCOM-STATCOM

Control & Protection UnitMC1 VSC1

STATCOM

iE1

I1

vDC

DC1

VXFSHN

s SHNBRKV

I

Vs'

Slide: 11

■■ Inductive operationInductive operationmeans E<V.means E<V.

■■ Capacitive operationCapacitive operationmeans E>V.means E>V.

A STATCOM Operating in Inductive andA STATCOM Operating in Inductive andCapacitiveCapacitive Modes Modes

E > V : Capacitive

STATCOM

E < V : Inductiveq

(c)I

(b)

IE

q

VE

V

V - E

Iq

TIEX

Xs

(a)

V

Iq

E

VXTIE

sr

Xr V

Slide: 12

■■ Regulates theRegulates thetransmission line’stransmission line’seffective reactanceeffective reactanceby connecting aby connecting acapacitor, parallelcapacitor, parallelwith a bypasswith a bypassswitch, in seriesswitch, in serieswith thewith thetransmission line.transmission line.

Thyristor-Switched Series Capacitor (TSSC)Thyristor-Switched Series Capacitor (TSSC)

V =C k C

X CXC CX

X (k=0, 1, ..., n)-j II X

LX

V

Slide: 13

■■ Regulates theRegulates thetransmission line’stransmission line’seffective reactanceeffective reactanceby connecting aby connecting acompensatngcompensatngvoltage in seriesvoltage in serieswith the line and inwith the line and inquadrature with thequadrature with theprevailing lineprevailing linecurretnt.curretnt.

Static Synchronous Series Static Synchronous Series CompensatorCompensator-SSSC-SSSC

VSC2Control & Protection Unit

SSSC

vDC

Vs

I2

MC2

iDC2 E2

SRSDS

V

1VES

XFSRSV2

dqI

BYPBRK

Vs'

Slide: 14

An SSSC Operating in Inductive andAn SSSC Operating in Inductive andCapacitiveCapacitive Modes Modes

■■ A series-injectedA series-injectedvoltage whilevoltage while–– leading theleading the

prevailing lineprevailing linecurrent, providescurrent, providesan inductivean inductivecompensationcompensation

–– lagging thelagging theprevailing lineprevailing linecurrent, providescurrent, providesa capacitivea capacitivecompensationcompensation

sin

(cos )δδδδ

I

90(c)

οοοο

sV

V

Vs'

V Xq

rQr = s

X X ' L q

X=Pr

rVr δδδδs

V VL Xq

V V

Vs

qV

L

Vs'

X

XVI

QrP , r

(a) (b)οοοο

οοοο

V

δδδδ r

Vs90

VV

s' sV

90Vq

δδδδ '

(d)

VI

X

r

οοοοVr

90

sV

VX

VI

δδδδ

r

Slide: 15

■■ Regulates the phaseRegulates the phaseangle of the lineangle of the linevoltage by a series-voltage by a series-connectedconnectedcompensating voltagecompensating voltagethat is in quadraturethat is in quadraturewith respect to thewith respect to theline voltage.line voltage.

A Phase Angle RegulatorA Phase Angle Regulator

s'B

sCPHASE ANGLEREGULATINGUNIT

V V

sA

sBV

(a)

s'CV

V

V

sC

s'A

VEXCITER

UNIT

VsB

s'B

sB

(b)s'AV

s'sBV

εεεεεεεε

V

s'sC

s'CVsA

V

s'B V

V V

VVs

C V s' C

sAV VV

s'sAs'A

s'A

Slide: 16

■■ Active and reactiveActive and reactivepower flow in thepower flow in theline is regulatedline is regulatedindependently.independently.

■■ Exchanged powerExchanged powerby the series unit isby the series unit isactive and reactive.active and reactive.

The Effect of a Series-Injected VoltageThe Effect of a Series-Injected Voltageon Power Flow in a Transmission Lineon Power Flow in a Transmission Line

Q

- R

Phase AngleRegulatorLine

P

V

1exchP X

Phase AngleRegulatorLine

(b)

with '+ R'ββββ

s'V

Vs

Vs's

-1 Qr @

δδδδ0

-0.5

0.5

r

δδδδ2

ReactanceCompensatorLine( = 0)Vd

V

0

-0.5

0.5P rn =

VoltageRegulatorLine

exch= V I

with '- R'

d

Pq= V I

exchQ

d

V

sV V q s'V

s's

V

-0.5

I

V

(a)

-1

X

XL

VrP ,

I r0

QV

r

270

270

LQ

Q

C

+ R

οοοο90

Pexch

180οοοο

οοοο90

= 0.2588s's

@r = 0Vs's

180οοοο

C

360οοοο

- R(c)

exch

οοοο ββββ

360

s's

οοοο

rn = Qr @V

οοοο ββββ= 0

= 0.2588rP

( )rnP , Qrn

@Vs's

r

1

VoltageRegulatorLine ββββ

Pexch

(d)

with '+ R'

P( = 0)

( )P , Qr* *r2

with '- R'

ReactanceCompensatorLine Pexch

r

Slide: 17

Characteristics of Power Flow ControllersCharacteristics of Power Flow Controllers■■ Traditional power flow controllersTraditional power flow controllers

–– each controls only one of the three parameters (voltage, reactance oreach controls only one of the three parameters (voltage, reactance orangle).angle).

■■ Single Voltage-Sourced Converter-based power flow controllersSingle Voltage-Sourced Converter-based power flow controllers–– each controls one of the transmission line parameters.each controls one of the transmission line parameters.–– can have fast dynamic response.can have fast dynamic response.

■■ Dual Voltage-Sourced Converter-based power flow controllersDual Voltage-Sourced Converter-based power flow controllers–– can exchange real power with the line and generate or absorb reactivecan exchange real power with the line and generate or absorb reactive

power.power.

Slide: 18

■■ Regulates theRegulates theactive and theactive and thereactive powerreactive powerflow in the lineflow in the lineindependently.independently.

■■ Regulates theRegulates theline voltage byline voltage byinjecting a shuntinjecting a shuntreactive currentreactive currentinto theinto thetransmission linetransmission line..

Unified Power Flow Controller-UPFCUnified Power Flow Controller-UPFC

VSC2Control & Protection Unit

MC1 VSC1

UPFC

iE1

I1

DCLS

vDC

DC1

VXFSHN

s SHNBRK

2I

MC2

iDC2 E2

SRSDS

V

1VES

XFSRSV2

dqI

BYPBRK

Vs'

Slide: 19

■■ Holding unity power factorHolding unity power factorwhile changing line activewhile changing line activepower.power.

■■ Sub-cycle performance ofSub-cycle performance ofa UPFC is not required ina UPFC is not required ina utility application.a utility application.

AEP UPFC Test ResultsAEP UPFC Test Results

P

Q

-300

-200

-100

0

100

200

300

0 10 20 30 40 50 60 70

Line Active Power (P) M W

Line Reactive Power (Q) M var

0.95

1

1.05

0 10 20 30 40 50 60 70

Inez Bus Voltage (pu)

-100-50

050

100150

0 10 20 30 40 50 60 70Time (s)

STATCOM Reactive Power (M var)

Slide: 20

What Are We Looking For in a Utility Application?What Are We Looking For in a Utility Application?

■■ A power flow controller that isA power flow controller that is–– reliablereliable–– independent regulator of active (independent regulator of active (PP) and reactive () and reactive (QQ) power flow) power flow–– fast enough for a utility applicationfast enough for a utility application–– inexpensiveinexpensive

Slide: 21

‘Sen’ Transformer Concept‘Sen’ Transformer Concept■■ Combines power flow control parameters, using aCombines power flow control parameters, using a

single-core three-phase transformer with load tapsingle-core three-phase transformer with load tapchangers,changers,–– voltagevoltage–– phase anglephase angle–– reactancereactance

■■ Regulates active and reactive power flow selectively,Regulates active and reactive power flow selectively,

■■ Regulates line voltage.Regulates line voltage.

Slide: 22

■■ Regulates line votage likeRegulates line votage likean autotransformer.an autotransformer.

■■ Controls active andControls active andreactive power flow in thereactive power flow in theline by a series-connectedline by a series-connectedcompensating voltage thatcompensating voltage thatis at any angle withis at any angle withrespect to the line voltage.respect to the line voltage.

‘Sen’ Transformer‘Sen’ Transformer

00

0

COMPENSATING-VOLTAGE UNIT

EXCITERUNIT

CB

N

A

sCV

VsB

VsA

b42

4

0c3

V1s'sC0

44

3

a3

b

4

02c

a1 I 1B

V

4

01s'sB

a2

44

0

4

b1

c1

1s'C

1s'B

V

V1CI

V0

1s'sA I 1A

V1s'A

Slide: 23

‘Sen’ Transformer Operation‘Sen’ Transformer Operation

VsBVs'sB

Vs'BV

V s'AV

s'sA

s As'sCV

V sCV s'C

sAVV

VsB

b2Vc3V

a1

V sC

a2

b1

Va3

c1

sAVV

V V

VsB

Vb3V c2

V sC

a1

s'sC

V c3

VV sC

c2Vb3 V

s'sB

V

V b2

sBV

V

VV

V V sA

c1

a3

ββββ

V

b1

a2

V s'sA

Slide: 24

■■ Line voltage isLine voltage isbounded by ±5% overbounded by ±5% overnominal voltage.nominal voltage.

■■ Full range of voltageFull range of voltageinjection is notinjection is notpermitted.permitted.

■■ Full capability of aFull capability of aUPFC is not utilized.UPFC is not utilized.

■■ ST can be modified toST can be modified tofit customers’ needs.fit customers’ needs.

Practical Practical Compensator’sCompensator’s Operating Range Operating Range

V

max

P

1.051β

δ(b)

εδ

rδ

Vs'Vs

1P =

s s'δ

0

-1

-0.5Qr @

rn

-10

100

X rV V0

0.95

0.8ε

Phase AngleRegulatorLine

VoltageRegulatorLine

s sδ

Vs's

V

(a)

Vs's

rδ

I 1.20

X

LXVs' s'

VI

V

P , rr Q

270

270

Q

β

A@ = 0V

Aοοοο90

s's = 0.2

r s's

180οοοο

P

οοοο90 21

A

β β

12εεεε

β

οοοο3β

r @Vs's = 0.2180

s'sV

360

(c)s's

Aοοοο

r @Vrn = Q

οοοο β= 0

s's

360οοοο4β

max−ε

V Vs' @34

οοοο β

= 0

P , Qrn( )

-0.5 VoltageRegulatorLine

rδ

= 0.2

-1

s'ss'V V@

Phase AngleRegulatorLine

0

Q r

(d)

rn

P , Q* *( )r r

β

Pδ

1A

r

Slide: 25

■■ Injects voltage fromInjects voltage from00οο to 120 to 120οο..

Limited Angle Operation of a ‘Limited Angle Operation of a ‘Sen’ TransformerSen’ Transformers'sA

44

VsC

0

4

c3

1c

VsB

Vs'sC

Vs'sB

a2

VsA a1

0

4

V

Vs'C

0

3b

b2

0

0

4

V

I B

s'B

0

4

s'AV

AI

Slide: 26

■■ Injects voltage fromInjects voltage from120120οο to 240 to 240οο..

Limited Angle Operation of a ‘Limited Angle Operation of a ‘Sen’ TransformerSen’ Transformer

4

s'sA

4

V sC a3

c1

V sB

0

2

Vs'sC

c

4

Vs'sB

a2

V sA

0

4

V

0V

0

43b

s'C

0

4

0

I C

V s'B

BI

b1

V s'A

I A

Slide: 27

■■ Injects voltage fromInjects voltage from240240οο to 360 to 360οο..

Limited Angle Operation of a ‘Limited Angle Operation of a ‘Sen’ TransformerSen’ Transformers'sA

44

VsC

c3

0

4

a3

VsB

0

2

s'sCV

c

4

Vs'sB

VsA a1

V

0

4

Vs'C

0

b2

0

I C

Vs'B

I B

0

4 b1

s'AV

AI

Slide: 28

■■ Controls the activeControls the activeand the reactiveand the reactivepower flow in thepower flow in theline by a series-line by a series-injected voltage thatinjected voltage thatis at any angle withis at any angle withrespect to the linerespect to the linevoltage.voltage.

A Power Flow Controller in a 2-Bus NetworkA Power Flow Controller in a 2-Bus Network

VsourceVX

source

PowerFlow

ControllerVs V

XLs' r

Slide: 29

Simulation of ST and UPFC Simulation of ST and UPFC (V(Vs’ss’s = 0.15 pu) = 0.15 pu)

■■ The exchanged power by the series unit of an STThe exchanged power by the series unit of an STand a UPFC are identical.and a UPFC are identical.

Variation of Exchanged Power with an ST

-30

-20

-10

0

10

20

30

0 100 200 300 400

Rotational Angle (degree)

Pow

er (M

W, M

var,

MV

A)

Pexch

Qexch

VAexch

Variation of Exchanged Power with a UPFC

-30

-20

-10

0

10

20

30

0 100 200 300 400

Rotational Angle (degree)

Pow

er (M

W, M

var,

MV

A)

Pexch

Qexch

VAexch

Slide: 30

■■ From 205From 205οο to 335 to 335οο, an ST, an STmaintains a higher linemaintains a higher linevoltage than a UPFC.voltage than a UPFC.

■■ From 0From 0οο to 205 to 205οο and 205 and 205οο

to 335to 335οο, a UPFC maintains, a UPFC maintainsa higher line voltage thana higher line voltage thanan ST.an ST.

Variation of Voltage at PCC

132

134

136

138

140

142

0 100 200 300 400

Rotational Angle (degree)

Vol

tage

(kV

)

ST

UPFC

Vs-nat

Simulation of ST and UPFC Simulation of ST and UPFC (V(Vs’ss’s = 0.15 pu) = 0.15 pu)

Slide: 31

■■ The variation of power flow, at the receiving-end ofThe variation of power flow, at the receiving-end ofthe transmission line, by an ST and a UPFC arethe transmission line, by an ST and a UPFC areidentical.identical.

Variation of Receiving-end Power with an ST

-150

-100

-50

0

50

100

150

200

0 100 200 300 400

Rotational Angle (degree)

Pow

er (M

W &

MV

ar)

Pr

Qr

Pnat

Qnat

Variation of Receiving-end Power with a UPFC

-150

-100

-50

0

50

100

150

200

0 100 200 300 400

Rotational Angle (degree)

Pow

er (M

W &

MV

ar)

Pr

Qr

Pnat

Qnat

Simulation of ST and UPFC Simulation of ST and UPFC (V(Vs’ss’s = 0.15 pu) = 0.15 pu)

Slide: 32

■■ Area of controllability inArea of controllability inthe the P-QP-Q plane for an ST plane for an STand a UPFC are almostand a UPFC are almostidentical.identical.

Q r vs Pr

-125

-100

-75

-50

-25

0

25

50 100 150 200

Pr (MW)

Qr

(MV

ar)

ST

UPFC

Simulation of ST and UPFC Simulation of ST and UPFC (V(Vs’ss’s = 0.15 pu) = 0.15 pu)

Slide: 33

Aerial View of AEP UPFC at Inez SubstationAerial View of AEP UPFC at Inez Substation

Slide: 34

Advantages and Shortcoming of an STAdvantages and Shortcoming of an ST■■ AdvantagesAdvantages

–– voltage regulationvoltage regulation–– independent control of active and reactive power (independent control of active and reactive power (P and QP and Q) flow) flow–– established transformer and load tap changer-based technologyestablished transformer and load tap changer-based technology–– limited angle operation with reduced amount of hardwarelimited angle operation with reduced amount of hardware–– reliable and less expensive power flow controllerreliable and less expensive power flow controller–– low operating costlow operating cost–– injection of line frequency voltage into the power system networkinjection of line frequency voltage into the power system network–– high enough response for most utility applicationshigh enough response for most utility applications

■■ ShortcomingShortcoming–– coarse voltage injection, which is acceptable for a utilitycoarse voltage injection, which is acceptable for a utility

application.application.

Slide: 35

Main Differences Between Power Flow ControllersMain Differences Between Power Flow Controllers

■■ Voltage RegulationVoltage Regulation■■ Independent Line Active andIndependent Line Active and

Reactive Power ControlReactive Power Control■■ Low installation and operating costsLow installation and operating costs■■ Reliability and high availabilityReliability and high availability■■ Injection of line frequency voltageInjection of line frequency voltage■■ Low leakage reactance in theLow leakage reactance in the

coupling Transformercoupling Transformer■■ Fast bypass switch not neededFast bypass switch not needed■■ Fast response for utility applicationsFast response for utility applications■■ Coarse voltage injectionCoarse voltage injection■■ Capability of independent reactiveCapability of independent reactive

power generation and absorptionpower generation and absorption

STST PARPAR VRTVRT UPFCUPFCXX X X XXXX XX

XX XX XXXX XX XXXX XX XXXX XX XX

XX XX XXXX XX XX XXXX XX XX

XX

Slide: 36

Main Differences Between Power Flow ControllersMain Differences Between Power Flow Controllers

■■ LossesLosses■■ Cost ($/Cost ($/kVAkVA))

STST PARPAR VRTVRT UPFCUPFC<1%<1% <1% <1% <1% <1% 3%-8%3%-8%15-2015-20 15-2015-20 10-1510-15 75-10075-100

Slide: 37

ConclusionConclusion■■ A new power flow controlling transformer is presented.A new power flow controlling transformer is presented.■■ ‘Sen’ Transformer‘Sen’ Transformer

–– uses traditional technology of transformer and tap changers.uses traditional technology of transformer and tap changers.–– uses proven technology that is reliable.uses proven technology that is reliable.–– provides four quadrant control of active power (provides four quadrant control of active power (PP) and) and

reactive power (reactive power (QQ) for an optimum system operation.) for an optimum system operation.–– provides more features than a PAR at the same cost.provides more features than a PAR at the same cost.–– displaces UPFC for most utility applications.displaces UPFC for most utility applications.

■■ An emerging power flow controller market can beAn emerging power flow controller market can beexploited with the right technology.exploited with the right technology.