A stochastic model for contact surfaces at polymer interfaces subjected to an electrical field

Morphology of the contact area between solid insulation materials ultimately determines the short-and longterm electrical properties of the complete insulation system. The main purpose of this paper is to propose a statistical model to examine the real area of contact between solid dielectric surfaces and secondly to verify and correlate the model outputs with experiments. The model computes real area of contact, number of contact spots and average cavity size at the interface as a function of elasticity, contact force and surface roughness. Then, using the average cavity size and the Paschen's law, the discharge inception field of the cavity (CDIE) is estimated. AC breakdown strength (BDS) testing of solid-solid interfaces was carried out, where cross-linked polyethylene (XLPE) samples with four different surface roughnesses were tested at various contact pressures. Following the increased contact force, the calculated average cavity size decreased by a factor of 4.08 - 4.82 from the roughest to the smoothest surface, corresponding to increased CDIEs by a factor of 2.01 - 2.56. Likewise, the experimentally obtained BDS values augmented by a factor of 1.4 - 1.7 when the contact pressure was elevated from 0.5 MPa to 1.16 MPa. A linear correlation between the CDIE and BDS was assumed, yielding a correlation coefficient varying within 0.8 1.3. when the 90% confidence intervals were considered, the range reduced to 0.86 1.05. This correlation suggests that interfacial breakdown phenomenon is strongly related to the interfacial cavity discharge. Hence, the proposed model is verified with experiments.