Roughness Enhanced Charge Injection and Field Dependent Conduction Mechanisms for Bipolar Charge Transport Models

Extruded HVDC cable systems contain a multitude of different interface types. Physical interfaces are introduced on-site when the outer semi-conductive layer is removed prior to installing a pre-molded joint or stress-cone onto the cable end. Such interfaces are characterized by surface roughness, which can locally enhance electric field and stimulate charge injection at microscale asperities. This work studies the impact of surface roughness on charge injection by performing space charge measurements on cable peelings and evaluating the observed charge evolution with a bipolar charge model. The behavior during both polarization and depolarization stages was investigated. A unique set of conduction and injection parameters is suggested allowing for realistic interpretation of charge accumulation and decay observed in the measurements.