Partial discharges in silicone gel in the temperature range 20-150°C

In order to increase the knowledge of the processes involved during the degradation of insulating silicone gels under ac stress, recordings of the activity of partial discharges (PD) are performed. Silicone gels are commonly used for the insulation and packaging of high voltage semiconductors such as IGBT modules. We worked on a commercially available dielectric silicone gel. Electrical and optical apparatus allows the measurement of PD's and their location, either on actual power module substrates, or in a point-plane gap. The temperature dependence of PD inception voltage is moderate, while the number of PD's and their charge steeply increases versus temperature. We show that the formation of cavities constitutes the main factor responsible for the degradation under ac conditions. The actual self-healing capabilities of silicone gels are also studied and discussed.