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Automatic Load Transfer – The Perfect Phantom Voltage SWEDE Conference Corpus Christi, TX

Automatic Load Transfer – The Perfect Phantom Voltage SWEDE Conference Corpus Christi, TX May 3, 2006 Kenton M. Brannan, P.E. CenterPoint Energy - Distribution System Reliability kenton.brannan@centerpointenergy.com. Facilities CenterPoint Energy Everyone’s Internet (EV1) Diagram

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Automatic Load Transfer – The Perfect Phantom Voltage SWEDE Conference Corpus Christi, TX

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  1. Automatic Load Transfer – The Perfect Phantom Voltage SWEDE Conference Corpus Christi, TX May 3, 2006 Kenton M. Brannan, P.E. CenterPoint Energy - Distribution System Reliability kenton.brannan@centerpointenergy.com

  2. Facilities CenterPoint Energy Everyone’s Internet (EV1) Diagram Scenario of Events Verification & Short-Term Fix Root Cause Finding a Long-Term Solution Recommendation Closure The Perfect Phantom Voltage

  3. CenterPoint Energy 2–2500 kVA pad mounted transformers 35 kV–480/277 V, Grd–Wye/Grd–Wye 115’ 1/0 AL UDG cable from terminal poles 110’ # 2 AAAC OVH lateral Everyone’s Internet (EV1) Data Center  Complete redundancy Backup generators can support 100% facility load 3,000 A automatic transfer switch (each service) Currently 2 services, 3rd expected in 2006 Facilities

  4. Diagram of Facilities

  5. County maint. crew blew C-phase lateral fuse C-phase voltage went to 0.0 Volts Transfer switch rolled load to neutral position C-phase secondary voltage reappeared Adequate voltage detected, roll-back initiated C-phase voltage again went to 0.0 Volts Cycle continued every few seconds for 20 min. EV1 staff blocked roll-back Scenario of Events

  6. Test scheduled to verify voltage All 3 fuses in place 284, 283, 284 V C-phase lateral fuse removed 284, 284, 276 V B-phase lateral fuse removed 284, 267, 284 V Short-Term Fix 10 minute roll-back block placed on each ATS Verification & Short-Term Fix

  7. Test – All Fuses in Place

  8. Test – C-phase Fuse Removed

  9. Contacted transformer manufacturer Discarded possibilities Ferro resonance Capacitive coupling C-phase voltage 100% load transfer Result of vectoral sum of A & B-phase fluxes Shifted by 180° due to nature of XFMR core Flux induces voltage on C-phase at 240° Root Cause

  10. Continue with 10 minute block Replace the transformer Delta-wye? Shift non-critical load from ATS to XFMR How much load? Add a small load to XFMR How much load? Future? Measure primary voltage 3-phase recloser on terminal pole $50,000  $150,000 for all 3 services Finding a Long-Term Solution

  11. Focus directed toward ATS IEEE task force for ATS Additional data acquired during test N/P sequence ratio: All 3 fuses in place N/P – 0.4 % C-phase lateral fuse removed N/P – 2.1 % B-phase lateral fuse removed N/P – 6.4 % Finding a Long-Term Solution

  12. Recommendation – 47N Phase Sequence Relay Installed at ATS controls Set at 2.0 % (negative/positive sequence) Cummins installed relay Test of relay scheduled Individual fuses removed Activity of ATS monitored Recommendation

  13. 47N relay prevented roll-back Determined successful EV1’s total installed cost $6,000 (per ATS) $18,000 for all 3 services Unique Situation CenterPoint Energy ATS controls manufacturer – Cummins Closure

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