Breakdown field in silicone gel under needle-plane geometry

The silicone gel is used in IGBT modules to isolate bondings driven by currents and submitted to high voltage of about several kV. The gel avoids the partial discharge inside the module that would lead to its failure even on its destruction. The goal of this study is to investigate the breakdown field of silicone gel in needle-plane geometry (with varying of the tip radius) under ac, dc and impulse voltages. The comparison of the results obtained under uniform field and divergent field was done. It is not possible to define a single value of the maximum field applicable to the gel. As in liquids, the field decreases when the size of electrodes is increased. However, by comparing the behavior of the gel and the silicone oil, there exists a difference for low tip radius. The space charge injected for small surfaces seems participate for increasing the breakdown field.