Influence of fast rise voltage and pressure on partial discharges in liquid embedded power electronics

Initiation of partial discharges at the highly stressed regions of an Insulated Gate Bipolar Transistor (IGBT) can lead to degradation of the insulation and eventual total breakdown of the system. In this work, an experimental setup has been designed for the study of partial discharges (PDs) under different voltage waveforms. PD behavior of IGBT insulation was investigated using conventional and optical techniques. Influence of pressure and voltage wave shape is documented. The test environment was first characterized with point-plane geometry under sinusoidal and slow rise square voltage of up to 20 kVpeak and fast rise square voltage of up to +50 kV. The measured electrical and optical PDs showed good correlation, revealing that optical PDs can be relied on for the characterization of PD phenomena. High slew rate of the square voltage reduced the inception voltage and increased magnitude. The PD pattern from the trench shows the existence of space charges. The PDs which occurred within the triple point region are most likely attracted along the board interface and become surface discharges. Pressure suppresses the initiation and propagation of the discharge.