112 / 2022-03-13 17:38:57

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

HVDC cable, XLPE, Crosslinking by-products, DC electrical properties, FTIR measurement

The peroxide crosslinking method with dicumyl peroxide (DCP) as agent is used to produce crosslinked polyethylene (XLPE) insulation for high voltage direct current (HVDC) cables, and degassing process is adopted to eliminate the by-products from DCP decomposition. However, due to the higher voltage level of HVDC cable and thicker insulation, degassing is more and more difficult and by-products inevitably remain in the insulation, which may affect the DC performance of XLPE. It is of great importance to study the correlation between electrical properties and by-products content of XLPE. In this paper, a 500kV DC cable degassing for 60 days is peeled to sheets with the thickness of 0.2mm, and the relative content of by-products in XLPE slices at different radial positions is obtained by Fourier transform infrared spectroscopy. The DC electrical properties such as DC conductivity, space charge density and breakdown strength of XLPE slices are also measured, and the correlation between by-products content and electrical properties of XLPE slices is analyzed. The results show that there are still by-products remain in the cable insulation after 60 days degassing, and the by-products content of internal insulation is higher than that of external insulation. There is a significant correlation between the electrical properties of insulation and the relative content of by-products, the linear correlation coefficient between the logarithm of conductivity and the content of by-products is near 0.9, and the correlation decreases gradually with the increase of temperature and field strength. The correlation coefficient r between space charge density and by-product content ranges from 0.69 to 0.96. The breakdown strength and by-products content are negatively correlated, the linear correlation coefficient r is about -0.9, and the negative correlation decreases with the temperature raises. The DC electrical properties of cable insulation are closely related to the content of by-products, and the controlling of by-products is particularly important for DC cables.