Presentation PST_en, Bucharest

8/2/2019 Presentation PST_en, Bucharest

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Siemens Workshop

Power Transmission and Distribution

Bucharest, March 2012

Bucharest, March 2012


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Page 2 Power Transmission and DistributionBucharest 2012

SIEMENS Transformers Austria, Weiz

Phase Shifting Transformers Basics and Application

Phase Shifting Transformers


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Contents

Purpose und function of PSTs

Categories and types

Operational considerations

Tap changer application

Testing

Recent PST units

Conclusion


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Basic funct ion o f a PST

In principle, a phase shifting transformer creates a phaseshift between the primary (source) and the secondary

(load) side

Usually, this phase shift can be varied under load

Sometimes, it can be made advance or retard

What is c a l led a Phase Shi f t er?

A phase shifting transformer is a tool to control the powerflow through specific lines in a complex power transmissionnetwork


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Pow er f low in pow er sys tem s needs t o becon t ro l led , due to

technical reasons (e.g. line overloading)

economical reasons (e.g. committed powertransfer at network node)

The need is increasing because of liberalization effects

Th is can be ach ieved w i th a

Phase Shi f t ing Transf orm er (PST)


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What does a Phase Shi f t er do?

It changes the effective phase displacement between the input

voltage and the output voltage of a transmission line, thuscontrolling the amount of real power that can flow in the line.

Because of the mainly inductive line impedance, inserting a voltagein phase or opposite to line voltage (changing magnitude of thevoltage) will have an impact on the reactive power flow only, whilea boost voltage with a phase angle perpendicular to the line voltage(creating a phase shift) actually influences the real power flow.


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How does th is phase sh i ft in f luence t he pow erf l o w ?

The natural current distribution is dependent on theimpedance of the lines

i1

i2

X1

X2

i total

VS VL

V


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i1

i2VS VL

V

V

The natural distribution may be rather inefficient, if X1 andX2 are extremely different.For example if X1 = 2*X2:


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Equal iza t ion o f cur rent s :

An additional voltage source must be introduced

i1 +

i

i2- iX1

X2

i total

VS VL

~

VS

VPST V1

V2


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This additional voltage source, perpendicular to the phasevoltage, generates a circulating current, increasing i1 anddecreasing i2: V1

i1+ i i2- iVPST

V2

V2

V1

VLVS VS

VPST


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P P QV

XN

0 0

2

cos sin sin

Pow er Transfer t hrough Phase Shi f t ing TransformerPrecondition: The voltage at two system nodes which are connected by a line with the

PST in series is assumed to be independent from the PST phase angle

VN Nominal system voltage, phase - phaseX Impedance of PST + line (X = XPST + Xline)

no load phase angle of the PST

P0 active power flow through PST at phase angle = 0Q0 reactive power flow through PST at phase angle = 0

P active power flow through PST at no load phase angle Q reactive power flow through PST at no load phase angle

Q P QV

XN

0 0

2

1sin cos cos


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-0,75

-0,5

-0,25

0

0,25

0,5

0,75

1

-0,50 -0,25 0,00 0,25 0,50 0,75 1,00 1,25 1,50

P(p.u.)

Q(

p.u.

)

PST pow er f low range as funct ion o ft hroughput load a t zero degree phase sh i f t


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Phase shi f t ing t ransform ers can be c lass i f iedfo r d i f fe ren t paramet ers : symmetrical non symmetrical quadrature - non quadrature

single core - two core

single tank - two tank


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Non-sym m etr ic a l sing le

core so lu t ion :

Advantageous for small phase angle,

Voltage and rating (appr. 15 -20)

Reversing switch operation is critical

Delta-connected exciting

winding, One tap winding One LTC One reversing change-over

switch

Phasor Diagram:

L1 S1

L2

S3

S2

L3

Winding Connection with Reversing Switch:

S3 L2 S1 L3 S2L1


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Symm etr ic a l sing le c ore

so lu t ion :

Load tap changers exposed to system

disturbances

Rating strongly limited by LTC

Delta-connected

exciting winding Two tap windings Two tap changers Two advance retard

switches

L1 S1

L2S3

S2L3

Phasor Diagram:

L1 S1 L2 S2 L3 S3Winding Connection with two ARS Switches:


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Zig-zag st y le so lut ion

Common application in Central Europe

Voltage regulation with phase shifting

Double wound substation

transformer Tap changer with phaseshifting option

Phasor diagrammax. +

advance

zero

H3

max. -

H2

H1

retard

H2H2

H3H3

H1H1

Winding arrangement and connections:

reversingswitch

Phase shift

selectorswitch

H1 H2H3X1 X2 X3


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Class ic so lu t ion :

Widely used for high voltages and ratings

Phase Shifting Transformer

Winding Arrangement and Connections:

S1 L1 S2 L2 S3 L3

a b c

Phasor Diagram:

a

bc

Secondary (regulating) circuit

S1

L2S3

S2L3

L1

Primary circuit

Symmetrical two core

design Series unit and excitingunit

One LTC


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Non-symm etr ic a l op t ion :

Solution for small phase angles

Standard UK solution

Quadrature Booster

Phasor Diagram:

a

bc

Secondary (regulating) circuit

S1

L2

S3 S2L3

L1

Primary circuit

Winding Arrangement and Connections:

S1 L1 S2 L2 S3 L3

a b c Dual core design

Series unit andexciting unit One LTC simple HV

connection


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Non-symm etr ic a l op t ion :

Mainly used in Europe

Combination of autotransformer with PST

Dual core design

Autotransformer and

single core phase shiftingunit Phase angle regulation

and in phase voltageregulation

1U

3 V 3 W

2 U 1 V 2V 1W 2 W

3U

1U

2U

1U

1V

2V

1W

2W

3U

3V

3W

1U

3 V 3 W

2 U 1 V 2V 1W 2 W

3U

1U

3 V 3 W

2 U 1 V 2V 1W 2 W

3U

1U

2U

1U

1V

2V

1W

2W

3U

3V

3W

1U

2U

1U

1V

2V

1W

2W

3U

3V

3W


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Phase sh i f t i ng t ransform ers in Operat ion :Variation of load voltage due to load current,ohmic components neglected

iLXPST

VS VL

~

VPST

VL0

j XPST* iL

iL

VL VSVL0

j XPST* iL VPST


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V ol t age a c ro ss PST


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arctan

cos

sin

I

Ix

II

x

N

PST

N

PST

1

Var ia t ion of phase shi f t due to t he load cur ren t

variation of phase angle due to load current

I current through PST

IN nominal PST current

xPST impedance of PST (pu)

angle between load voltage and load current(cos = power factor of load)


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d e l t a a l p h a

a l p h a ( l o a d ) = a l p h a ( n o - l o a d ) + / - d e l t a a l p h a

0 ,00

1 , 00

2 , 00

3 , 00

4 , 00

5 , 00

6 , 00

7 , 00

8 , 00

9 , 00

10 , 00

11 , 00

12 , 00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

i m p e d a n c e ( % )

Rei he1 Re i he2

Reihe 1=p.f. 0.9, Reihe 2=p.f. 1.0


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Effec t of load on effe ctive phase a ngle

-6 0

-4 5

-3 0

-1 5

0

15

30

45

-16 -12 -8 -4 0 4 8 12 16

tap pos ition

p

h

ase

an

g

le

(d

eg

re

e)

pf 0 .8 , 100% In p f 1.0, 100% In pf -0 .8 , 100% In no - load


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Impedance as low as possible, minimum valuedetermined by short circuit requirements

With lower impedance, the no load phase angle can bereduced

Lower no load phase angle means lower design rating,lower weight, lower cost.

For a g iven phase shi f t under load, designopt i m izat ion is poss ib le :


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Bypass breaker cons idera t ions

Due to the PSTs impedance, inserting the PST withphase angle zero normally reduces the load flow

A minimum advance phase angle is necessary to restore

the original load flow condition

Therefore, by-passing the PST might be advantageous incertain conditions

On the other hand, lightning strikes can also appear with

the PST by-passed Internal stresses have to be investigated carefully for this

condition


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PSTs can be designed with fixed or variable phase angle.

For a variable phase angle design, a load tap changer(LTC) and a regulating winding is required.

In general, the regulating winding and therefore the LTCmust be designed for the maximum design rating of thePST.

The maximum regulating capacity (switching capacity perstep times the number of steps) is limited by the capacity

of available tap changers.

Tap changer app l ica t ion


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Tap Changer Application

Power needed to reach a certain displacement in phase angle

Palpha = 2 x Pthr x sin alpha/2

Is proportional to the throughputpower and almost proportional to thephase angle

Palpha rating of the series winding resp. phase shift ing power (MVA)Pthr throughput power (MVA)alpha no-load phase angle (degree)


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Calculation of the max. possible throughput power at a given phase

angle

Assumption:

Approx. 5500kVA step capacity of the LTC (includes retard operation only advanced 6000kVA possible)

Palpha = 5.5 x k x 3 (phases) x 32 (steps) x / sin alpha/2

k.correction factor (function of max. phase angle)

Example: 48 degrees

Palpha = 5.5 x 0.914 x 3 x 32 x x sin 48/2 = 593 MVA

Difference to a transformer:For a troughput rating of 600MVA and a in-phase voltage regulation of +/-15% only 0.15 x 600 = 90 MVA

have to be switched by the on-load tap changer.


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Throughput power versus no-load phase angle

step capacity 5000 - 6000 kVA, +/32 steps

0

10

20

30

40

50

60

70

80

90

200 400 600 800 1000 1200 1400 1600 1800

throughput power (MVA)

no-loadp

hase

angle

(de

gree)

5500kVA

5000kVA

6000kVA


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Testing

Test ing phase shi f t i ng t ransform ers :

Heat run

PST fully assembled minimized deviation of loss distribution during short circuit condition access to all windings for resistance measurement

Specific requirements:

Dielectric tests

PST fully assembled and connected necessary to get conditions

like in service

Induced voltage test

tests at zero and maximum phase shift


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Testing

Heat run t es t :

For resistance measurement, all these connections can be opened

Temporary bushings inserted at all connections between series and exciting unit

~

Series Transformer

Exciting Transformer

Auxiliary

Bushings

Short circuit connection


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Testing

Induc ed vol tage t es t :

Application of an additional step-up transformer is avoided by proper tap selection

Temporary bushings are connected to the regulating winding

S2 L2 S3 L3S1 L1

Series Transformer

Exciting Transformer

~ Auxiliary bushings


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Testing

L ight n ing impu lse tes t :

Recommended test if by-pass breaker is provided - at least for tap position zero (0)

Only the primary windings of one phase are shown

L2S2 S2 L2

Standard LI test:

Source- andload- terminalconnected

Special LI test:


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Testing

-50

0

50

100

150

0 40 80 120T(s)

V(%)

Applied voltage and typical wave shape of voltage at crossover during lightningimpulse test with source and load side terminals connected

L ight n ing impu lse s t resses in t he ser ies w ind ing


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Recent PST units

Phase Sh i f t ing Transformer

Two-tank designTwo-core design

Classical design PST

700MVA, 230kV, 60Hz

32no load ( 24Taps); 22.2..-41.8load

uk: 11.1% Tap 0; 17.4% Tap 24

Noise Level < 74 dB(A) with fans


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Recent PST units




700MVA, 230kV, 60Hz

32no load (24 taps);

22.2at rated load - extreme advance

-6.3at rated load - mid tap (0)

-41.8at rated load - extreme retard

uk: 11.1% Tap 0; 17.4% Tap 24


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Recent PST units




800MVA, 230kV, 60Hz

35no load ( 32Taps); load 25.3..-44.9

uk: 11.4% Tap 0 ; 17.6% Tap 32

Noise Level < 77dB(A)


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Recent PST units



300 MVA, 138 kV, 60 Hz

25.0at no load ( 16 taps);


-5.4at rated load - mid tap -35.6at rated load - extreme retard

uk: 9.5% Tap 0; 18.6% Tap 16

Noise level < 70 dB(A)

Single-tank designTwo-core design


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Recent PST units




575 MVA, 345 kV, 60 Hz

37,8no load (16 taps);


-4.9at rated load - mid tap -48.0at rated load - extreme retard

uk: 8.5% Tap 0 (NR); 17.94% Tap 32 (16R)

Noise level < 68 dB(A) @ 345 kV


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Recent PST units



234 MVA, 138 kV, 60 Hz

25no load ( 16 taps)



-35.6at rated load - extreme retard uk: 7.62% Tap 0; 18.25% Tap 16

Noise limit - Octave Band

Limits M1-R New York

125 250 500 1000 2000 [Hz]


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Recent PST units


Single-tank designSingle-core design

Delta hexagonal PST

150MVA, 138kV, 60Hz

32.9no load ( 16 taps)

30.1at rated load tap 1

0.0at rated load tap 17

uk: 5% tap 1; 0% tap 17


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Recent PST units




1200MVA, 400kV, 50Hz

24no load (32 taps);



-31.4at rated load - extreme retard

uk: 9.25% Tap 0; 13.0% Tap 32

Noise power level < 80 dB(A) - sound house


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Conclusion

Phase shifting transformers look similar to normalpower transformers, and they are manufacturedusing the same technology.However, there are some aspects in design andtesting, which only appear in PSTs and therefore

require special consideration.

The classical two-tank two-core solution offers thegreatest security in operation at higher voltagelevels as the LTC is not directly exposed to systemdisturbances.

The single-core solution offers economicadvantages at lower system voltage levels.


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Thank you foryour attention !

Presentation PST_en, Bucharest

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