A new dielectric response model for water tree degraded XLPE insulation - part a: model development with small sample verification

Water tree degradation in underground XLPE insulated cables is a growing, worldwide problem. This form of degradation is ultimately fatal for affected cables, and therefore the detection of damaging trees in power cable insulation is vital for distribution companies to avoid catastrophic failure. Dielectric response measurements, in both the time and frequency domains, can generate valuable information about the condition of the cable. However, the interpretation of how these dielectric response measurements relate to water tree density and length is a difficult task. This paper will present a new dielectric response model for water tree degraded XLPE insulation. The model is based on finite element analysis to determine the electrical behaviour of water tree degraded insulation. Preliminary simulations will verify the model development by comparing the results to small sample pulsed electro-acoustic (PEA) measurements performed by other researchers. The importance of a strong non-linearity mechanism for accurate modelling will also be elucidated.