Phase Shifting Transformers. Presented by

Transcription

1 Phase Shifting Transformers Presented by

2 Phase Shifting Transformers (PST s) (a.k.a. Phase Angle Regulators) VS φ S P V V S = X L L X L sin( φ φ ) L S VL φ L PST s are power flow control devices between synchronous systems. VS φ S P X PST V + α VL + X S = S L X PST L X L sin( φ φ + α) VL φ L The phase angle α governs the flow of power.

3 Active vs. Reactive Power Transfer

4 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 φ1 > φ2 G G φ2 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

5 Uses of PST s To allow for optimum loading of parallel lines a) without PST The natural current distribution is dependent on the impedance of each line. if X 1 > X 2, then I 1 < I 2 and I 2 may drive its line to its thermal or dynamic stability limits b) with PST With the introduction of V PST, a circulating current i is generated to equalize the currents on both lines.

6 Definition of Advance and Retard Phase Angles V L V S voltage at source side α adv0 0 V L0 voltage at load side at no load V S V S α adv0 advance phase angle at no load, load voltage leads source voltage. This sign is defined as positive in IEEE C and IEC α ret0 retard phase angle at no load, α ret0 V L 0 load voltage lags source voltage. This sign is defined as negative

7 Phase Shift under Load (retard)

8 Phase Shift under Load (advance)

9 Impact of PST Impedance on Phase Shift

10 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

11 ATCO Electric s Two Core Design PST (with symmetric voltages) V 1S V 2S Main (exciting) unit Series unit V 1L V 2L V 3S V 3L

12 Phasor Diagram to illustrate Quadrature Voltage

13 Regulating windings Technical Issues - 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 < kv - short circuit thermal limit of ka for 2 secs. - small step voltage --> many operations

14 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 Transformers A report to the Substation Subcommittee of the IEEE Power System Relaying Committee prepared by Working Group K1 - IEEE C57.135

15 Topologies

16 Energization and operating issues during bypass Peak voltage of 140% of applied impulse at crossover 1.2 x 50 s lightning impulse

17 Cores for ST and ET

18 Core Insulation & Cooling Ducts

19 Tank Fabrication

20 Throat connecting ST&ET Tanks

21 Foundation - Winding assembly

22 Winding processing & sliding

23 Coil Nesting and lead processing

24 Top Yoke Assembly

25 Top Frame Installation

26 Tap leads

27 Tap leads routing to LTC

28 LTC Connections

29 Tanking Active Part

30 Photos of PST s in Factory 450 MVA 138 kv ± 58 single-core design with reactors 550 tons Length of internal connections ~ 5 km

31 Photos of PST s in Factory Active part, HV side of 500 MVA 400 / 132 kv + 22 in ± 3 x 7 steps, ± 12 % in ± 13 steps on HV

32 Photos of PST s in Factory Active part, HV side of 500 MVA 400 / 132 kv + 22 in ± 3 x 7 steps, ± 12 % in ± 13 steps on HV

33 2750 MVA Quadbooster in Test

34 2750 MVA Quadbooster at Site

35 Acceptance Tests in the Factory

36 Challenges in Transport (240 t for the Shunt Unit)

37 Challenging Transport

38 Extensive Acceptance Tests on Site

39 Extensive Acceptance Tests on Site

40 Transformer Short Circuit