Oil-immersed transformer is an important part of power network, "liquid-solid" oil-paper insulation system as the main insulation material of oil-immersed transformer, its insulation state is related to the safety and stability of transformer operation. Moisture invaded is one of the main reasons for deterioration of oil-paper insulation performance. At present, the effective method to diagnose oil-paper insulation moisture content is polarization/depolarization current method (PDC), but the current polarization/depolarization current measurement has low excitation voltage (less than 200 V), which cannot reflect the real time dielectric properties of the equipment under normal operating conditions. Therefore, it is necessary to study the dielectric response characteristics and conductance characteristics of "liquid-solid" oil-paper insulation system with different moisture content under high voltage excitation. In this paper, a high voltage time-domain dielectric response measurement platform was built to prepare oil-paper insulation samples with different moisture content, and the influence of moisture content and high and low voltage on oil-paper insulation time-domain dielectric response characteristics was studied. The results show that the polarization current curve and the initial part of depolarization current increase with the increase of water content and voltage gradient. The electrical conductivity of oil-paper insulation increases significantly with the increase of applied voltage and almost linearly with the increase of moisture content. The conductivity of mineral oil decreases first and then increase with the growth of applied voltage. The results of this paper provide reference for PDC measurement of transformer under high voltage.

PDC, time domain dielectric, insulation, relaxation behavior