Tom Ernst GE Digital Energy Craig Talbot Minnesota Power

Transcription

1 Tom Ernst GE Digital Energy Craig Talbot Minnesota Power

2 Introduction Traditional 3-phase testing method Traditional 1-phase testing method Alternate 1-phase testing method Application examples

3 3-Phase testing can be challenging Straight forward magnitude & phase angles Requires 6 high-current test set channels 1-phase testing Requires only 2 high-current test set channels Requires non-obvious multipliers Does not simulate real-world loading on Deltawye transformers

4 There is always a way to do this better

5 Alternate 1-phase testing method Requires only 2 high-current test set channels Simulates real-world 1-phase loading conditions No phase shifts No non-obvious multipliers Suitable for commission testing: tests the transformer installation not the relay settings

6 Slope characteristic tests Requires simultaneous injection of test currents into a minimum of 2 relay windings Some test sets do not include 6 high-current channels Magnitude relationship of the currents based on the transformer 3-phase voltage ratio

7 Slope characteristic tests Phase shift between test currents can be challenging for delta grd wye transformers Function of the transformer internal and external connections: phases A, B & C might not be on bushings 1, 2 & 3 Requires thorough understanding of 3-phase power Same transformer can be 30 lag or 30 lead

8 Typical delta - grd wye transformer and associated 3- phase test currents (30 lag)

9 Typical delta - grd wye transformer with rolled phasing and associated 3- phase test currents (30 lead)

10 3-Phase testing connections for a 30 lag transformer

11 Slope characteristic tests Checks the functionality of each phase Only requires 2 current channels May require multipliers and phase shifts that are not obvious (Delta Grd Wye transformers)

12 Relay Test Set 1-Phase testing connections Differential Relay Ia Ib Ic Ia Channel 1 Ib Channel 2 Ic Com

13 Some alternate ideas are better than others

14 Slope characteristic tests Connections are related to the transformer internal and external 3-line diagrams Very affective for commissioning Simulates real-world load and short circuit conditions No non-obvious multipliers No non-obvious phase shifts

15 Differentially balanced 1- phase throughcurrent for a delta - grd wye transf (30 lag) Test Currents to Relay 2.5@ @0 H1 115,000 13,800/7970 GY 20 MVA A B C 100@0 H2 N1/N2 = 115/8 H3 200/5 A C (H3) C (X3) Nameplate H1 H3 Installed A (H1) X3 X0 B (H2) A (X1) X0 B (X2) H2 X1 X0 X2 X1 X2 X3 3.61@ /5 A 1443@0 A B C

16 Differentially balanced 1- phase test connections for a delta - grd wye transf (30 lag) Differential Relay 3.61@180 Relay Test Set Ia Ib Channel 1 Ic Ia Ib Channel 2 Ic Com

17 Differentially balanced 1- phase throughcurrent for a delta - grd wye transf (30 lead) Test Currents to Relay 2.5@ @0 115,000 13,800/7970 GY 20 MVA A B C 100@0 H3 H2 H1 N1/N2 = 115/8 200/5 A C (H1) A (X3) X0 C (X1) Nameplate H1 H3 Installed A (H3) X3 X0 B (H2) B (X2) H2 X1 X0 X2 X3 X2 X1 3.61@ /5 A 1443@0 A B C

18 Differentially balanced 1- phase test connections for a delta - grd wye transf (30 lead) Differential Relay 3.61@180 Relay Test Set Ia Ib Channel 1 Ic Ia Ib Channel 2 Ic Com

19 Slope characteristic tests Test currents calculated based on N1/N2 turns-ratio not voltage ratio 3 multiplier inherent No 0-seq filtering multiplier required Currents always 180 apart Test results clearly indicate if differential phase shift is set correctly

20 Differentially balanced through-current condition with correct phase shift setting

21 Differentially balanced through-current condition with incorrect phase shift setting

22 Slope verification with angle of winding 2 rolled until relay trips. S = 0.13/0.50 = 0.26 (26%)

23 Test connections for a 2 winding 30 degree lag delta-wye connection transformer Test ID Winding 1 (delta) connections Winding 2 (wye) connections A In on A & out on C A B In on B & out on A B C In on C & out on B C

24 Test connections for a 2 winding 30 degree lead delta-wye connection transformer Test ID Winding 1 (delta) connections Winding 2 (wye) connections A In on A & out on B A B In on B & out on C B C In on C & out on A C

25 Wake up. This is the interesting part

26 Transformer nameplate

27 3-line installation diagram - differentially balanced 1-phase load N1/N2 = 115/ A 1200/5 MR 300/5 Tap 0 A (H1) C (H3) B (H2) A (X1) C (X3) X0 B (X2) 1200/5 MR 1200/5 Tap A

28 Test definitions

29 Transformer nameplate

30 A B C 3-line installation diagram - differentially balanced 1-phase load A (H3) C (H1) B (H2) A (X3) X0 B (X2) C (X1) 600/5 MR 400/5 Tap 160 A 0 N1/N2 = 115/ /5 SR 2240 A

31 Test definitions

32 Transformer differential tripped on external feeder fault Caused by wrong angle setting Alternate method not used No load available at time of construction for inservice checks Using the alternate method might have prevented the trip

33 HV Winding 1 Differential Current LV Winding 2 Differential Current Waveform Capture

34 Traditional 3-phase testing method can be challenging Traditional 1-phase testing method does not simulate real-world loading Alternate 1-phase testing method simulates real-world and tests the settings against the installation

35