Root Cause Analysis of Transformer and Generator Stator Failure on Hydropower Plant in Indonesia

Abstract

This paper presents an investigation related to the transformer and generator failure on a hydropower plant. Comprehensive visual inspection was conducted after the failure and the result showed visible dry band arcing mark along the surface of a transformer cable termination. Further analysis on transformer and generator historical assessment data followed by simulation process using apparatuses specification data and configuration were conducted to get possible root cause of the failure. Transformer historical assessment data showed abnormal result on insulation resistance test which increased the possibility of ground fault and also short circuit between high voltage and low voltage winding of the transformer during failure. According to ground fault and short circuit simulation between high voltage and low voltage winding of the transformer, the voltage at high voltage side of the transformer reached 1.73 times higher than the nominal value while the generator stator voltage reached over 7 times higher than the nominal value. Therefore, the possible cause of transformer and generator stator failure was internal ground fault and arcing between high voltage and low voltage winding of the transformer which caused flashover on cable termination attached to the high voltage side of the transformer and insulation breakdown of generator stator.