Space Charge Behavior and Electrical Breakdown Strength of XLPE Film Sandwiched between Semiconducting Layers

In the ordinary space charge distribution measurement using pulsed electro-acoustic (PEA) system, a semi-conductive (SC) layer is inserted between a high voltage metal electrode and a measurement sample to improve a mismatch of acoustic impedance between them. On the other hand, as a grounded electrode, an aluminum (AI) plate is usually used to increase a sensitivity of the measurement. However, in an actual XLPE (cross-linked polyethylene) cables, an inner and an outer SC layers are used as the electrodes, and XLPE insulating layer is sandwiched by them. Therefore, to understand the actual space charge effects in the actual cable on a breakdown property, it is important to study the space charge accumulation characteristics in XLPE using such electrode system. In this paper, we measured the space charge distribution and external circuit current density in XLPE sandwiched by the SC layers under dc high electric stress. As a result, a larger current was observed in the XLPE sandwiched by the SC layer, but the fracture strength appeared to be similar to that in the XLPE of a conventional electrode system. From this result, it is thought that even if XLPE is sandwiched between SC layers, it would not show any effect on the dielectric strength.