Understanding the Life and Ageing of XLPE Insulation considering Free Energy Barrier Concept

Under operation, insulating materials undergo ageing due to multiple stresses such as electrical, thermal, mechanical etc. Due to ageing life expectancy of the electrical equipment is reduced. In this work, life and ageing of XLPE cable insulation is studied under electro-thermal stress considering the concept of free energy barrier. Due to applied stresses, ageing of insulation occurs and thereby reduces the free energy barrier gap. The change in free energy barrier due to ageing is estimated considering a phenomenological linear model. The estimated life of XLPE insulation is comapred with DC-DMM model. Further the correlation between applied stress and free energy barrier is studied. It is observed that the estimated lifetime of XLPE matches fairly well with DC-DMM model. The free energy barrier is seen to change with applied electro-thermal stress. The local electric field or accumulated charge density increases with decrease in barrier gap.