Comparative Analysis of Dielectric Characteristics of Differently Manufactured High Voltage Insulation System for Generator Stator Winding

In the year 2018, two turbo generators (TG) of 150 MVA, 11KV rating at different power plants were tested for condition assessment by the authors. TG1 was at a base load power plant and completed 25 years of service. TG2 was at combined cycle power plant and served for 15 years. Based on the year of installation, it was established that high voltage insulation system of stator winding in TG1 was processed with resin rich (RR) thermo set technology and that in TG2 was processed with global vacuum pressure impregnation (GVPI), an advanced technology. In this paper, comparative finding on RR and GVPI technologies for insulation of stator winding in these two TGs was presented for familiarization. Condition assessment tests such as insulation resistance (IR), dielectric loss factor (tan δ), partial discharge (PD), natural frequency test (NFT) and slot wedge tightness (WTD) had been carried to detect the defects in insulation. Analysis of the test data was presented to interpret the dielectric behavior of these two variants. It was concluded that the dielectric parameters of insulation systems in both TGs were at satisfactory levels due to timely corrective actions on TG1 stator winding and due to GVPI processed insulation on TG2 stator winding.