Gill station, PG&E

1. Gill station, PG&E 2 MVA transformer 22/4.3 kV Westinghouse URS reactive OLTC

2. A case study TASA rating 4* (four star) >>extreme abnormal dissipation of energy is noted<<.

3. TASA

4. Unit Substation Case Study Oil tests indicate significant gassing taking place in tap changer Testing scheduled before overhaul Both static and dynamic testing performed on unit

5. Phase X1 DRM testing identified a few contacts with high resistance. Abnormal transitions also identified

6. Phase X2 Abnormal transitions also identified. DRM testing identified one stationary contact with high resistance.

7. Phase X3 Multiple spikes identified indicating possible pitting or coking. DRM testing identified two contacts with high resistance.

8. End result • Significant wear on three contacts • Initial hypothesis validated • One stationary contact in Phase 1 and 2 had significant coking • Two contacts in Phase 3 had some coking identified during the testing • Reversing switch in all three phases showed significant coking

9. Coking on Selector Switch – X1

10. Coking

11. Coking