Phase Shifting Transformers Rev1 - University of Albertaapic/uploads/Forum/phase shifter...

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Phase Shifting Transformers

Presented by

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Phase Shifting Transformers (PST’s)(a.k.a. Phase Angle Regulators)

SSV φ∠ LLV φ∠LX

)sin( LS

L

LS

X

VVP φφ −=

PST’s are power flow control devices between synchronous systems.

SSV φ∠ LLV φ∠LXPSTX −+ α

)sin( αφφ +−+

= LS

LPST

LS

XX

VVP

The phase angle αgoverns the flow of power.

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Active vs. Reactive Power Transfer

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Uses of PST’s

� To control power flow in electrical systems

� To correct for phase angle differences- Network coupling by enabling power transfer under acceptable parameters

G Gφ1 > φ2 φ2

G

Design power flow

Block parasitic power flow due to phase angle differences in feeding network(s)

Distribute power to different customers in a defined way

G Avoid circulating power flows

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Uses of PST’s

� To allow for optimum loading of parallel lines

a) without PST

b) with PST

The “natural” current distribution is dependent on the impedance of each line.

if X1 > X2, then I1 < I2

and I2 may drive its line to its thermal or dynamic stability limits

With the introduction of VPST, a circulating current �i is generated to equalize the currents on both lines.

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Definition of Advance and Retard Phase Angles

ααααret0VL

0

VS

ααααadv0

VS

VL

0

VS voltage at source side

VL0 voltage at load side at no load

αadv0 advance phase angle at no load,load voltage leads source voltage. This sign is defined as positive in IEEE C57.135 and IEC 62032

αret0 retard phase angle at no load,load voltage lags source voltage. This sign is defined as negative

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Phase Shift under Load (retard)

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Phase Shift under Load (advance)

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Impact of PST Impedance on Phase Shift

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Types of PST’s

� Single Core Designs- Polygon squashed delta

- Asymmetrical extended delta

- Symmetrical extended delta

- Full wye-wye

� Two Core Designs

- Quadrature booster

- Symmetrical grounded wye (most common and most flexible)

Options:

With addition of voltage regulation

Combined transformer and phase shifting function

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ATCO Electric’s Two Core Design PST (with symmetric voltages)

V1S

V2S

V3S

V1L

V2L

V3L

Main (exciting) unit

Series unit

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Phasor Diagram to illustrate Quadrature Voltage

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Technical Issues� Regulating windings

- OLTC max. voltage range of � 85 kV- large space and size requirements for regulation windings (designed to handle not just a certain % of the rated power)- capacitive coupling of large portions of the regulating windings can lead to high recovery voltages during OLTC operation

� Tap changer capacity- max. regulation voltage range of � 85 kV- max. # of operating positions < 35- max. tap voltage < 4 - 5 kV / tap- max. rated through current of 3000 A- max. of � 6 MVA / tap- lightning impulse voltage across regulation range < 600 – 820 kV- short circuit thermal limit of 30 – 36 kA for 2 secs.- small step voltage --> many operations

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Protection Issues

� Source and load current exhibit same phase shift as voltages� Regular transformer differential relay would trip!

� Special differential protection schemes needed

� More information in:- Protection of Phase Angle Regulating TransformersA report to the Substation Subcommittee of the IEEE Power SystemRelaying Committee prepared by Working Group K1

- IEEE C57.135

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Topologies

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Energization and operating issues during bypass

1.2 x 50 �s lightning impulse

Peak voltage of 140% of applied impulse at crossover

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Cores for ST and ET

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Core Insulation & Cooling Ducts

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Tank Fabrication

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Throat connecting ST&ET Tanks

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Foundation - Winding assembly

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Winding processing & sliding

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Coil Nesting and lead processing

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Top Yoke Assembly

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Top Frame Installation

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Tap leads

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Tap leads routing to LTC

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LTC Connections

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Tanking Active Part

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Photos of PST’s in Factory

450 MVA

138 kV

± 58 °

single-core design with reactors

550 tons

Length of internal connections ~ 5 km

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Photos of PST’s in FactoryActive part, HV side of 500 MVA 400 / 132 kV + 22°in ± 3 x 7 steps, ± 12 % in ± 13 steps on HV

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Photos of PST’s in FactoryActive part, HV side of 500 MVA 400 / 132 kV + 22°in ± 3 x 7 steps, ± 12 % in ± 13 steps on HV

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2750 MVA Quadbooster in Test

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2750 MVA Quadbooster at Site

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Acceptance Tests in the Factory

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Challenges in Transport (240 t for the Shunt Unit)

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Challenging Transport

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Extensive Acceptance Tests on Site

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Extensive Acceptance Tests on Site

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Transformer Short Circuit