Analysis of the Trend of Insulation Aging in Stator Winding of Off-Line and On-Line Steam Turbine Generator

In this paper, a steam turbine(S/T) generator(68.2MVA, 13.8kV) has been in service for more than 17 years. To assess the insulation aging condition of the stator winding of the S/T generator after prolonged operation, diagnostic tests were recently conducted both during off-line and on-line. The off-line diagnostic test primarily involves the measurement of alternating current, dissipation factor(tanδ), and partial discharge(PD). The insulation aging are anticipated through routine diagnostic tests conducted during off-line for seven years. In contrast, while the S/T generator is in operation, the analysis of insulation condition is focused solely on measuring PD for two years. This approach enhances the accuracy of determining the insulation condition, thereby improving the operational reliability.