Effect of pressure and length on interfacial breakdown between two dielectric surfaces

The phenomenon of interfacial AC breakdown is considered. Two pieces of EPDM (ethylene-propylene diene monomer) rubber were pressed together and a special jig was conceived to provoke arcing along the interface. The voltage at which breakdown occurred was measured and its dependence on interfacial length and pressure established. In the absence of silicone grease at the interface, breakdown voltage showed a linear dependence on pressure. With silicone grease, breakdown values were consistently higher and reached a plateau at higher pressures. The dependence on length was similar to what is observed for bulk dielectrics. While the dielectric strength curve for a silicone-greased interface decreased with length, the one with a dry interface, although it followed the same general behavior, exhibited an unexplained dip at around 4 mm