Analysis of partial discharge to high voltage motor stator windings

Partial discharge(PD) tests are used to evaluate the insulation condition of 6.6 kV motor stator windings. These tests were conducted using a conventional partial discharge detector (PDD), turbine generator analyzer (TGA) and partial discharge analyzer (PDA). Off-line PD measurements were performed on using the PDD. PD magnitude of the No. 1 and 2 stator windings was about 8,200 pC and 2,400 pC at the normal line-to-ground voltage, respectively. Two stator windings have been equipped with two 80 pF epoxy-mica couplers (one per stator winding). The PD pulses from sensors were measured with the TGA and PDA instruments at 3.81 kV, 4.76 kV and 6.6 kV. The PDD, TGA and PDA showed that off-line PD magnitude, the maximum PD magnitude (Qm) and normalized quantity number (NQN) increased with increase of ac voltage. The PDD, TGA and PDA test results showed that internal and slot discharges were detected in voids of the groundwall insulation and at the surface of stator winding. The results of the PDD, TGA and PDA measurements can be directly correlated with the pattern, the magnitude and the number of PD.