Insulating Liquids, an Alternative to Silicone Gel for Power Electronic Devices

This paper studies the breakdown voltage for different insulating materials encapsulating power electronic devices. A comparison between some liquids and silicone gel is carried out. The 50 Hz AC voltage tests were performed according to the IEC 60156 specifications. The same process was applied to the DC voltage tests due to a lack of standard procedure concerning DC voltage tests on liquids. In each case, a ceramic substrate was placed in a container filled with the insulating material. A voltage was applied between two electrodes glued on the substrate. Mineral, both synthetic and natural ester oils and silicone gel were tested. The voltages of breakdown between oils were quite similar in AC and DC. The gel is more resistant to DC stress even though its self-healing is less than the liquids investigated.