IN THE PAST 15 YEARS, INSURANCE INDUSTRY DATA HAVE indicated that stator end-winding vibration has become the most important cause of generator failure. The source of vibration is the current creating magnetic forces between coils, and it may be amplified due to mechanical resonance. End-winding vibration leads to failure by insulation abrasion or copper fatigue cracking. The extent of the repair caused by the ensuing damage
and the loss of production have proven to be very costly.
After 13 years of operation, one such failure occurred to a two-pole, 95-MW generator at a plant in Indonesia, which had an associated loss of US$40 million. This article describes the failure mechanism, possible reasons why end-winding vibration has become a more important issue in the past decade, and a new International Electrotechnical Commission (IEC) Technical Specification (TS)
60034-32 on methods to detect the problem well before in-service failure. A case study on the affected generator will show how a repeat stator winding failure was avoided using these tools.