Effect of Test Voltage Waveforms on Partial Discharge Inception Voltage Considering Different Environmental Conditions

Electrical machines (EMs) used in transportation applications are subjected to high voltage stress due to the elevated DC link voltage and fast rise time of switching devices. These design choices promote partial discharge (PD) activity in winding insulation, which in turn jeopardizes EM safe operations. PD tests can be conducted using either sinusoidal or impulse voltage waveforms; however, variations in test results may arise from different test voltage types, particularly when considering the harsh ambient conditions encountered by transportation EMs. Therefore, it is essential to assess this discrepancy and its dependence on ambient conditions. In this study, the partial discharge inception voltage (PDIV) is measured under four distinct ambient conditions: 100°C at 1000 mbar; 100°C at 400 mbar; 180°C at 1000 mbar; and 180°C at 400 mbar. The mismatches between test results are emphasized and a stress voltage waveform enhancement factor is proposed. Based on this factor, the PD risk could be simply evaluated by referring to the PD test results obtained by applying a sinusoidal voltage as a stress waveform.