Static electrification testing of Texas Utilities 345-20.9 kV, 650 MVA generator step-up transformer under controlled factory conditions
Comanche Peak Nuclear Power Plant, with two 1150 Megawatt units, has two 345-20.9 kV, three-phase, 650 MVA transformers connected in parallel. The transformers have had a long history of hydrogen generation, and one of the Unit No. 2 transformers failed in 1983 while energized from the system for plant construction power. The failed unit was repaired and returned to Comanche Peak, and there was no evidence of static electrification involvement in the failure. During the time from installation to commercial operation in 1990 for Unit No. 1 and 1992 for Unit No. 2, the transformers were backfed from the system as needed to provide construction power. There was little regard paid to the operation of the cooling systems other than assuring the cooling was running. The transformers on unit No. 1 were subjected to several unusual electrical events - ferroresonance in 1981 and over excitation in 1983, with the generation of gasses of great concern. The decision was made to install a new transformer and return the old unit to the factory for diagnostic testing to determine the cause for the generation of combustible gas, primarily hydrogen. The dielectric integrity of the transformer could be quantified and decisions made concerning the replacement of the remaining transformers. After testing, the transformer was disassembled for forensic evaluation and rebuilt for return as a spare or to replace another transformer while undergoing repairs. Deformation of the bottom of the tank was discovered with large dents in the bottom protruding inward approximately one and one-half inches. With the concern of decreased clearances or displaced flux shields in the tank, an inspection opening was cut in the end of the transformer near the bottom. While investigating the deformation, evidence of partial discharge activity was discovered at the bottom of the high-to-low insulation; a location where static electrification damage has been observed in other large shell-form transformers.
- Research Organization:
- Electric Power Research Inst. (EPRI), Palo Alto, CA (United States)
- OSTI ID:
- 96468
- Report Number(s):
- EPRI-TR-105019; CONF-9409355-; TRN: 95:018954
- Resource Relation:
- Conference: Static electrification in power transformers workshop, Milwaukee, WI (United States), 28-30 Sep 1994; Other Information: PBD: May 1995; Related Information: Is Part Of Static electrification in power transformers: Proceedings; PB: 369 p.
- Country of Publication:
- United States
- Language:
- English
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