Condition assessment program on aged high voltage insulation of in-service turbine generator

Outdated turbine generators (TG) with epoxy resin rich thermo set insulation system are in operation in numerous captive power plants of process industries. The dielectric served more than the expected life of 25 to 30 years and reaching even 50 years. The asset managers want to evaluate the dielectric strength of these age barred insulation of windings. The authors got an opportunity to perform diagnosis tests on one of the in- service venerable machines and evaluation results are presented in this paper. This paper focused on interpretation of test results of condition assessment protocol on dielectric insulation system of 40MVA, 11kV high voltage TG of 43 years old. Evaluation is done on the test results of insulation resistance, polarization index, leakage current, dielectric dissipation factor and capacitance. In addition, modern diagnosis tests viz. polarization depolarization current analysis (PDCA), phase resolved partial discharges (PRPD) and corona probe are conducted to supplement the traditional dielectric tests to probe the defects in depth. The test data and 3D PD histograms of these new techniques provide classification and localization of insulation defects. The paper concludes with the rehabilitation recommendation on insulation to prolong the life.