B-6 Testing Numerical Transformer Differential Relays - IEEE

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B-6 Testing Numerical Transformer Differential Relays - IEEE

  1. 1. IEEE Rural Electric 2009 Testing Numerical Transformer Differential Relays Steve Turner Beckwith Electric Co., Inc.
  2. 2. Testing Numerical Transformer Differential Relays <ul><li>Commissioning versus Maintenance Testing </li></ul><ul><li>Types of Transformer Differential Protection: </li></ul><ul><li>Restrained Phase Differential </li></ul><ul><li>High Set Phase Differential </li></ul><ul><li>Ground Differential </li></ul>INTRODUCTION
  3. 3. Testing Numerical Transformer Differential Relays <ul><li>Topics: </li></ul><ul><li>Transformer Differential Boundary Test (Commissioning) </li></ul><ul><li>Ground Differential Sensitivity Test (Commissioning/Maintenance) </li></ul><ul><li>Harmonic Restraint for Transformer Inrush (Maintenance) </li></ul>INTRODUCTION
  4. 4. Testing Numerical Transformer Differential Relays <ul><li>Commissioning </li></ul><ul><li>Common Practice : </li></ul><ul><li>Test all numerical relay settings – </li></ul><ul><li>verify settings properly entered </li></ul><ul><li>Easily facilitated using computer – </li></ul><ul><li>automate test set & store results </li></ul><ul><li>Hundreds of tests are possible – </li></ul><ul><li>numerical relays have many settings </li></ul>
  5. 5. Testing Numerical Transformer Differential Relays <ul><li>Commissioning </li></ul><ul><li>Final Goal </li></ul><ul><li>Ensure the transformer is properly protected for the particular application </li></ul>
  6. 6. Testing Numerical Transformer Differential Relays R G 46 Typical Distribution Transformer 46 : Negative-Sequence Overcurrent Element ( sees ground faults through bank ) R G : Grounding Resistor (Industrial Load)
  7. 7. Testing Numerical Transformer Differential Relays R G 46 E + Z T Z T Z T 3R G 46 I 2 Sensitive setting for ground fault - overreach for phase-to-phase fault
  8. 8. Testing Numerical Transformer Differential Relays Transformer Differential Characteristic Boundary Test I 2 I 1 87 Y Y Y Y I 1 = Winding 1 per unit current (A, B or C-phase) I 2 = Winding 2 per unit current (A, B or C-phase) 3 elements per function (A, B & C-phase) * Simulate Through Current
  9. 9. Testing Numerical Transformer Differential Relays Differential Characteristic Operating Equations I d = |I 1 – I 2 |, Differential Current I r = |I 1 | + |I 2 |, Restraint Current 2
  10. 10. Testing Numerical Transformer Differential Relays Differential Characteristic I d I r Minimum Pickup (per unit) Percent ( % ) Slope X Y % = Y X *100%
  11. 11. Testing Numerical Transformer Differential Relays Differential Characteristic I d I r Minimum Pickup Percent Slope Trip Region Block Region
  12. 12. Testing Numerical Transformer Differential Relays Matrix I d I r [ ] = <ul><li>-1 </li></ul><ul><li>½ ½ </li></ul>[ ] * I 1 I 2 [ ]
  13. 13. Testing Numerical Transformer Differential Relays Inverted Matrix I 1 I 2 [ ] = ½ 1 -½ 1 [ ] * I d I r [ ]
  14. 14. Testing Numerical Transformer Differential Relays Differential Characteristic Test Current Equations I 1 = 0.5*I d + I r , Winding 1 Test Current (per unit) I 2 = -0.5*I d + I r , Winding 2 Test Current (per unit)
  15. 15. Testing Numerical Transformer Differential Relays Differential Characteristic Test Points I d I r Minimum Pickup Percent Slope Minimum Pickup = 0.2 per unit Slope = 28.6% 1 2 3 4
  16. 16. Testing Numerical Transformer Differential Relays Differential Characteristic Test Points (Per Unit) I d I r I 1 I 2 1 0.2 0.3 0.4 0.2 0.2 0.7 0.8 0.6 0.4 1.4 1.6 1.2 0.6 2.0 2.3 1.7 2 3 4 TABLE 1
  17. 17. Testing Numerical Transformer Differential Relays Delta-Wye Differential Characteristic I 2 I 1 87 Y Y Y I 1 = Winding 1 per unit current (A, B or C-phase) I 2 = Winding 2 per unit current (A, B or C-phase) 3 elements per relay (A, B & C-phase) * Simulate Through Current DAB
  18. 18. Testing Numerical Transformer Differential Relays Delta-Wye Differential Characteristic ( Relay Internally Compensates Test Currents ) I A1 relay = I A1 /TAP1 DAB WINDING I B1 relay = I B1 /TAP1 I C1 relay = I B1 /TAP1 I A2 relay = (I A2 - I B2 )/(TAP2*SQRT(3)) WYE WINDING I B2 relay = (I B2 - I C2 )/(TAP2*SQRT(3)) I C2 relay = (I C2 - I A2 )/(TAP2*SQRT(3)) TAP# = MVA# kV# LL *CTR#*SQRT(3)
  19. 19. Testing Numerical Transformer Differential Relays Delta-Wye Differential Characteristic ( Single-Phase Test for A-Phase Element ) I d I r I 1 I 2 0.2 0.7 0.8 0.6 2 From TABLE 1 : I A1 = I 1 *TAP1 I A2 = I 2 *TAP2*SQRT(3) I A1 test = 0.8*TAP1 I A2 test = 0.6*TAP2*SQRT(3)
  20. 20. Testing Numerical Transformer Differential Relays Ground Differential Element Sensitivity Test Directionality (I 0 vs. I G ) Ground Fault Location along Windings
  21. 21. Testing Numerical Transformer Differential Relays Ground Differential Element Directional Element +90 o -90 o I G I 0 Disabled if |3I 0 | less than 140 mA (Improves Security for CT saturation during external faults) Internal External
  22. 22. Testing Numerical Transformer Differential Relays Ground Differential Element Pickup Operate When : |3I 0 – I G | > Pickup
  23. 23. Testing Numerical Transformer Differential Relays Ground Differential Element Sensitivity Test Power System Parameters : <ul><li>Source Impedance ( Varies ) </li></ul><ul><li>X T = 10% </li></ul><ul><li>R F ( Varies ) </li></ul><ul><li>Ground Fault Location (5% from Transformer Neutral) </li></ul>
  24. 24. Testing Numerical Transformer Differential Relays Ground Differential Element R F Coverage vs. Source Strength
  25. 25. Testing Numerical Transformer Differential Relays Ground Differential Element Pickup Setting Cold Load Pickup Reclosing into Single-Phase Load Pickup > Unbalance Directional Element Disabled if 3I 0 Low I G R
  26. 26. Testing Numerical Transformer Differential Relays I G2 = 0.3 Amps @ 177 o 3I 0 (2) = 0.136 Amps @ 58 o ( Threshold = 0.14 Amps ) |CTCF*3I 0 (2) – I G2 | = 0.75 Amps Original Pickup = 0.3 Amps
  27. 27. Testing Numerical Transformer Differential Relays I G2 CTCF*3I 0 (2) INTERNAL EXTERNAL I OP New Pickup = 1.0 Amps Directional Element
  28. 28. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush COMTRADE PLAYBACK <ul><li>Waveform Sources : </li></ul><ul><li>Events from Numerical Relays </li></ul><ul><li>Events from Digital Fault Recorders </li></ul><ul><li>Simulate using Transient Software </li></ul>
  29. 29. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush Traditional Approach <ul><li>2 nd Harmonic Restraint </li></ul><ul><li>Cross Phase Blocking </li></ul>
  30. 30. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush Auto-Transformer Model 600 MVA Auto-Transformer (Tertiary Winding DAC) wye wye delta 13.2 kV 345 kV 230 kV W 1 W 2 W 3
  31. 31. Testing Numerical Transformer Differential Relays Auto-transformer Characteristics Z HM = 0.01073 per unit Z HL = 0.04777 per unit Z ML = 0.03123 per unit = 0.0140 per unit = -0.0029 per unit CTR W1 = 1200:5 (wye connected) CTR W2 = 2000:5 (wye connected) Even Harmonic Restraint during Inrush Auto-Transformer Model Z H = Z M = Z L = = 0.0340 per unit
  32. 32. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush Auto-Transformer Model TAP1 = 600 MVA 345 kV * 240 * SQRT(3) TAP2 = 600 MVA 230 kV * 400 * SQRT(3) = 4.18 = 3.77 Minimum Pickup* = 0.5 per unit Slope = 25% * Original Pickup = 0.45 per unit
  33. 33. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush Energize Bank with Heavy A-Phase Residual Flux Total Phase Current
  34. 34. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush Energize Bank with Heavy A-Phase Residual Flux 2 nd Harmonic Phase Current
  35. 35. Testing Numerical Transformer Differential Relays Even Harmonic Restraint I even = (I 2 2 + I 4 2 ) 1/2
  36. 36. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush Energize Bank with Heavy A-Phase Residual Flux 4 th Harmonic Phase Current
  37. 37. Testing Numerical Transformer Differential Relays Even Harmonic Restraint during Inrush A-Phase Current (Winding 2)
  38. 38. Testing Numerical Transformer Differential Relays CONCLUSIONS
  39. 39. Testing Numerical Transformer Differential Relays <ul><li>Transformer Differential Boundary Test ( Commissioning ) </li></ul><ul><li>Ground Differential Sensitivity Test (Commissioning/Maintenance) </li></ul><ul><li>Harmonic Restraint for Transformer Inrush (Maintenance) </li></ul>CONCLUSIONS
  40. 40. Testing Numerical Transformer Differential Relays QUESTIONS

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