Research on the Correlation Between DC Electrical Properties and By-product Content of XLPE Insulation for HVDC Cable

Abstract

Cross linked polyethylene (XLPE) is a common insulating material for high voltage direct current (HVDC) cables. With the elevation of the voltage level for HVDC cable, the insulation layer becomes thicker and by-products inevitably remain in the insulating layer even after degassing, which affects the DC properties of XLPE. In this paper, the relationship of crosslinking byproduct and electric property for 500kV DC cable has been investigated after degassing for 60 days. The relative content of by-products in XLPE slices at different radial positions was determined by Fourier transform infrared spectroscopy. The DC conductivity, space charge density and breakdown strength of cross-linked polyethylene sheets were measured, and the correlation between the content of byproducts and the electrical properties of cross-linked polyethylene sheets was analyzed. The content of cross-linking by-products in cable is closely related to the electrical performance of cable. With the increase of by-product content, the conductivity of cable increases and the insulation performance decreases. At the same time, it will also aggravate the accumulation of space charge. The increase of conductivity and the accumulation of space charge lead to the decrease of cable breakdown field strength. Therefore, controlling the content of crosslinking by-products is particularly important for DC cables.