Failure analysis of dry-type power transformer

This paper provides the failure analysis of a three-phase, dry-type, silicone resin vacuum-pressure encapsulated, 750/1000 kVA, AA/FA, 34.5 kV-480 Y/277-V, delta-wye power transformer. Transient overvoltage switching surge propagation through the transformer winding and protection margin is discussed. An arbitrary sensitivity of 10 pC at 120% rated voltage generally used for the partial discharge tests at the factory may be inadequate for the design of the failed transformer.