Encapsulation Insulation Failure Mechanisms of Power Module in Circuit Breakers

Efforts in utilizing power electronic devices as circuit breakers, specifically solid-state and hybrid DC circuit breakers, have resulted in numerous advantages compared to the traditional electro-mechanical approach. This development has propelled the integration of power electronic devices into circuit breaker technology, offering a promising strategy. However, when it comes to providing power module for specific applications, ensuring their electrical insulation reliability remains a significant challenge, particularly under harsh environmental conditions and situations requiring high voltage, large current, and high switching frequency. Therefore, there is a crucial need for a comprehensive understanding of the insulation failure mechanisms and corresponding mitigation methods for power modules encapsulation. In this paper, we have successfully achieved the precise localization of partial discharge phenomena at the triple junctions within a 6.5 kV commercial power module using a specialized partial discharge detection and location system. Furthermore, an in-depth examination of the insulation failure process in a conventional simulated packaging structure, comprising a DBC substrate filled with silicone gel, is undertaken. This examination includes an investigation into the charge dynamics at the triple junction, the growth of electrical trees, and the characterization of insulation degradation by-products. This study will contribute to the elucidation of the underlying causes of insulation failures of power modules.