Understanding the effect of non-uniform ageing on dielectric response of transformer insulation

In this paper a distributed parameter model of differential time-domain dielectric spectroscopy (DTDS) is proposed. It is aimed at addressing the limitations of the previously used universal model of DTDS for studying the effect of non-uniform ageing on the dielectric response of transformer insulation. The universal model of DTDS assumes that dipoles are subjected to the same ageing condition when they disperse randomly in insulation medium. It adopts the summation of a number of exponential functions to describe the collective effect of different dipoles on dielectric relaxation process. In contrast, the proposed distributed parameter model of DTDS considers that dipoles are subjected to different ageing conditions separately. It divides DTDS into a series of time windows and each exponential function in universal DTDS model is modelled as the summation of DTDS from each time window. The correlation between the characteristic parameters of the model of DTDS and insulation ageing is investigated. Accelerated ageing experiments and dielectric response measurements are conducted to verify the proposed distributed parameter model of DTDS.