Propagation of Electrical Tree and Characteristic of Partial Discharge at Gel-Substrate Surface in IGBT

Partial discharge (PD) and electrical tree initiated at the gel-substrate-copper electrode triple point are the main reason for insulation failure of IGBT. This paper focuses on the electrical tree propagation and PD characteristics at gel-substrate interface. Based on a real-time testing platform for electrical tree and PD measurement under AC voltage, the electrical tree propagation process was investigated and the mechanism was further analyzed. Furthermore, the degrees of damage to insulation by electrical trees under different voltages were quantitatively elucidate based on statistical methods. Besides, PD characteristic was analyzed based on phase-resolved partial discharge (PRPD) during electrical tree propagation process. The results show that electrical tree propagation process can be divided into two stages of growth and stagnation. The mechanism of electrical tree is forward extension of the cavities under strong PD effect. The dark traces can weaken PD activity. The electrical tree has much longer growth time and causes more damage at higher voltage. The PD activity weaken with electrical tree propagation.