Pre-breakdown phenomena in synthetic ester and silicone oils for power transformers

This paper reports on the initiation and propagation of streamers in synthetic ester and silicon oils for power transformers. The study is carried out under dc voltage using a point-plane electrode arrangement. We especially analyze the initiation voltage of streamers as well as the associated current and light emitted by these streamers. The influence of hydrostatic pressure (P_H) on these characteristic parameters is also investigated. Itpsilas shown that the initiation threshold voltage (U_i) of streamers is higher with a positive point than with a negative one whatever the liquid ; U_i increases quasi-linearly with PH. The values of U_i are higher in silicon oil than in synthetic ester (tetraester).