Electrical treeing behaviours in cross-linked polyethylene cables after thermal ageing

Long-term thermal ageing might have impacts on the physicochemical properties of cross-linked polyethene(XLPE)cables,thereby influencing their electrical behaviours,such as electrical treeing initiation and growth.The main objective of this work is to report the effects of thermal ageing on the electrical treeing behaviours(initiation and growth)in XLPE cable insulation.For this purpose,the electrical treeing initiation and growth test were performed in accelerated thermal samples.In addition,Differential Scanning Calorimetry and Fourier Transform Infrared Spectroscopy were utilised to investigate corresponding changes in the microstructures of materials.In addition,a correlation was established between electrical treeing behaviours and physicochemical properties during the thermal ageing process.Test results indicate that the thermal ageing process should be divided into three phases,and the re-crystallisation reaction is considered the primary reason for the increase of average electrical tree initiation voltage(AETIV).Furthermore,the thermal ageing index Xc is correlated to AETIV and the propagation rate of the electrical tree.As equivalent relationships have been established between the relative decrease value w of indexes AETIV,the propagating rate and Xc,this method can be employed to predict the changing pattern of electrical treeing initiation voltage and the propagating rate in future research.