Space charge formation in XLPE at polarity reversal under high temperature

We measured space charge and external circuit current simultaneously in XLPE sandwiched by semi-conductive layers. Space charge accumulation characteristics are important factor to develop a DC power transmission cable. Many research works have been carried out using pulsed electro-acoustic (PEA) method to investigate the space charge behavior in insulating material like cross-linked polyethylene (XLPE), which is a typical base insulating material for the DC cable. In the ordinary PEA system, the space charge is usually measured with electrodes of an aluminum (Al) plate and a semi-conductive (SC) layer. However, actual XLPE cables have inner and outer semi-conductive layers, and XLPE insulating layer is sandwiched by them. Therefore, it is important to understand the space charge accumulation characteristics with such electrode system. In this investigation, we also observed the space charge behavior at polarity reversal of the applied voltage. As the results, a positive packet-like charge, which was observed in XLPE with Al-SC electrode system, was also observed in XLPE with SC-SC electrode system under a relatively high DC stresses, and it made a large distortion of the electric field.