Electric Field Distribution Considering the Byproducts Inhomogeneity of Crosslinking Insulation in HVDC Cable

Crosslinking byproducts are inevitable in XLPE cable crosslinking process, and will affect the DC dielectric properties of cable insulation and cause the electric field distortion. It is of great importance to effectively control the cleanness and eliminate the byproducts during crosslinking. In this paper, the byproducts contents of degassed HVDC cable insulation and undegassed HVDC cable insulation are analyzed by using the infrared spectrometer. It is found that after degassing the byproducts content decreases, while the standard deviation of radial distribution of byproducts increases 144% at most. Then, the DC conductivity at 10~50 kV/mm and 30~70 °C is measured for cables insulation. Result shows that the DC conductivity decreases but the standard deviation of logarithm of XLPE insulation conductivity increases 400% at most after degassing. Moreover, the electric field distribution has been simulated in XLPE insulation of the HVDC cables with different degassing periods. After degassing, the maximum electric field strength increases from 35.9 kV/mm to 40.4 kV/mm under 1.85U0 and full load condition. The results show that the inhomogeneity level of byproducts have a significant impact on electric field distribution of XLPE cable insulation, which should be taken into consideration in HVDC cable manufacture.