Investigation of the 'non-linear' dielectric response of water tree-aged XLPE cables in the time and frequency domain

Heavily water tree-aged cables show a so-called 'non-linear' dielectric response with respect to the voltage whose origin is still unknown and which is difficult to relate to the actual condition of the cable insulation. However, the 'non-linear' behaviour is one possible diagnostic criterion. The aim of the work presented in this paper is to investigate this 'non-linear' dielectric response in the time and frequency domain, as well as to correlate both domains by different mathematical approaches. The 'non-linear' behaviour of the dielectric response is found to be different in the time and frequency domain. Also a transition from 'non-linear' to 'linear' behaviour of the dielectric response can be observed in some cases above a certain voltage.