A comparison of space charge behaviors in coaxial cable and film sample under temperature gradient

Space charge in DC cables affect the long-term reliability of the cable during operation. A temperature gradient (TG) develops across the cable insulation due to Joule heat in the conductor. Extensive researches on space charge in film insulations under TG have been reported. However, up to date, it is still questionable whether the measurement results of film samples can directly reflect the space charge characteristics in an actual coaxial cable. In this study, the space charge behavior in a 10 kV XLPE cable was investigated under different temperatures and electrical stresses using an improved pulse electro-acoustic (PEA) measurement system. The results show that the coaxial geometry and the TG both enhance hetero-charge accumulation near the cable outer semi-conductive layer. Space charge in film samples sliced from the same cable under the same conditions were also measured and compared to that in the cable. It is found that the space charge behaves similarly in terms of charge variation laws and distributions under different electrical stresses and TGs regardless of the type of sample structure, the two space charge measurement methods show well equivalence.