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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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Purpose und function of PSTs
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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Purpose und function of PSTs
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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Purpose und function of PSTs
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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Purpose und function of PSTs
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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Purpose und function of PSTs
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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Purpose und function of PSTs
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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Purpose und function of PSTs
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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Purpose und function of PSTs
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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Purpose und function of PSTs
-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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Categories and types
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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Categories and types
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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Categories and types
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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Categories and types
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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Categories and types
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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Page 18 Power Transmission and DistributionBucharest 2012
Categories and types
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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Page 19 Power Transmission and DistributionBucharest 2012
Categories and types
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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Operational considerations
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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Operational considerations
V ol t age a c ro ss PST
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Operational considerations
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Operational considerations
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Operational considerations
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Operational considerations
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Operational considerations
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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Operational considerations
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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Operational considerations
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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Operational considerations
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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Operational considerations
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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Tap changer application
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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Tap changer application
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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Page 34 Power Transmission and DistributionBucharest 2012
Tap changer application
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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Page 36 Power Transmission and DistributionBucharest 2012
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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Page 37 Power Transmission and DistributionBucharest 2012
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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Page 38 Power Transmission and DistributionBucharest 2012
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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Page 41 Power Transmission and DistributionBucharest 2012
Recent PST units
Phase Sh i f t ing Transformer
Classical design PST
Two-tank designTwo-core design
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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Page 42 Power Transmission and DistributionBucharest 2012
Recent PST units
Phase Sh i f t ing Transformer
Two-tank designTwo-core design
Classical design PST
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
Phase Sh i f t ing Transformer
Classical design PST
300 MVA, 138 kV, 60 Hz
25.0at no load ( 16 taps);
14.4at rated load - extreme advance
-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
Phase Sh i f t ing Transformer
Classical design PST
Two-tank designTwo-core design
575 MVA, 345 kV, 60 Hz
37,8no load (16 taps);
27.6at rated load - extreme advance
-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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Page 45 Power Transmission and DistributionBucharest 2012
Recent PST units
Phase Sh i f t ing Transformer
Classical design PST
234 MVA, 138 kV, 60 Hz
25no load ( 16 taps)
14.4at rated load - extreme advance
-5.4at rated load - mid tap (0)
-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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Page 46 Power Transmission and DistributionBucharest 2012
Recent PST units
Phase Sh i f t ing Transformer
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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Page 47 Power Transmission and DistributionBucharest 2012
Recent PST units
Phase Sh i f t ing Transformer
Classical design PST
Two-tank designTwo-core design
1200MVA, 400kV, 50Hz
24no load (32 taps);
16.6at rated load - extreme advance
-5.3at rated load - mid tap (0)
-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 !