Remaining Life Assessment of the Generator Stator Insulation: A Case Study on Suralaya Coal Fired Power Plant in Indonesia

Abstract

The failure of large generators in generating stations and industrial plants is mainly caused by the failure of the stator winding insulation. The combination of electrical, mechanical and thermal stresses that are accumulated by the number of start-stop times and operating hours can reduce the residual dielectric voltage as the main cause of the deterioration on the insulation. In this study, the remaining life assessment of the generator stator insulation was conducted based on the functional relationship between stresses and remaining dielectric voltage in the worst and average cases. The case study was conducted on the fourth of generator unit in SURALAYA Coal Fired Power Plant in Indonesia that had the service life of over 25 years. To validate the assessment results, partial discharges (PD) test was performed on the stator coils of the generator. Based on the results of evaluation, it was found that the remaining life of the fourth of generator insulation at the worst case had been come to end. For the average case, the remaining life of insulation for Unit 1 and Unit 2 was 12 year, while for Unit 3 and 4 was 17 year. Then from the validation results using the PD test, there was an evidence of the discharging of voids or delamination within the insulation, where the internal discharging was seen to be the most dominant factor from the discharge pattern. However, the PD magnitudes were still within reasonable limits, where the magnitude of the maximum discharge was 3,500 pC for the U phase, while in the V and W phase was 7000 pC, hence it was not categorized as an anomaly.