Field power-factor testing of transformer insulation and operating experience

One requirement of a field test on transformers is that weaknesses which develop in bushing or winding insulation be readily located and failures prevented. This has been effectively accomplished in the American Gas and Electric Company system by a power-factor testing program of transformer insulation which was initiated in the fall of 1933. For some 18 months prior to this time, a field testing program for oil circuit-breaker insulation had been in progress. As pointed out in previous publications,^1,4 these tests had proved satisfactory particularly in locating faulty bushings and bad oil circuit-breaker insulation. It is the purpose of this paper to discuss the tests we have made on transformer winding insulation, the methods used in locause of progressive faults has been detected and eliminated without need of major repairs. This procedure has helped materially in keeping equipment in first-class operating condition, in preventing failures, and in realizing substantial monetary savings.