Choosing Expert Evaluations of Diagnostic Tests of Electric Insulation for High-Voltage Electric Machines

This article provides the results of studying the influence of test voltage frequency on the dynamic parameters (dielectric losses and characteristics of partial discharges) of micaceous insulation of stator winding for high-voltage (HV) electric machines. The tests have been conducted using mockup samples of stator insulation with an artificial defect in the front area. It has been established that the low-frequency (0.1 Hz) test voltage increases the dielectric loss tangent and, at the same time, reduces the peak apparent charge of external partial discharges compared to the tests at power frequencies. The established ratios must be taken into account when choosing expert diagnostic evaluations during high-voltage electric-machine tests.