Partial Discharges and Electroluminescence Measurements on Power Electronic Substrates Embeded in Liquids

This paper presents an experimental study of partial discharges (PD) and electroluminescence properties of dielectric liquids (dibenzyltoluene & silicone oil) embedding a Silicon Nitride $(\mathrm{S}\mathrm{i}_{3}\mathrm{N}_{4)}$ ceramic substrate. With silicone oil partial discharges appear above 3 kV whereas no PD activity is recorded with dibenzyltoluene up to 6 kV. This indicates that with this $\mathrm{S}\mathrm{i}_{3}\mathrm{N}_{4}$ substrate, partial discharges actually originate from the liquid, contrary to previous similar measurements carried out with other ceramics $(\mathrm{A}l_{2}\mathrm{O}_{3},\ \mathrm{A}\mathrm{l}\mathrm{N})$. Optical light detection and visualization also shows that DBT is highly electroluminescent. Silicone oil and $\mathrm{S}\mathrm{i}_{3}\mathrm{N}_{4}$ show no electroluminescence, making it possible to study PD activity with a high sensitivity via measurement of emitted light. Since light measurements can be done whatever the shape of voltage wave, contrary to electrical PD recording, the detection of PDs with fast rise voltage becomes possible.