Temperature dependency of wave propagation velocity in MV power cable

Propagation velocity of high frequency signals, e.g. from partial discharge, is a vital parameter for time domain power cable diagnostic techniques. The propagation velocity is mainly dependent on the permittivity of the insulation material, which can be affected by external parameters like temperature or water ingress. This paper focuses on the influence of temperature on the propagation velocity in medium voltage (MV) cables. Laboratory scale tests are performed for both PILC and XLPE cable. Test results show that the high frequency signal propagation velocity for XLPE will increase with the temperature rise while PILC has opposite behaviour. The variation of propagation velocity of XLPE is confirmed by data of a power cable subjected to strong load cycling monitored over eight months.