Moisture effect on the dielectric response and space charge behaviour of mineral oil impregnated paper insulation

Oil-paper insulation system is widely used in power transformers and cables. Moisture is recognized to the ?enemy number one? for transformer insulation except for temperature [1]. Moisture is not only one of the most important factor which can accelerate the transformer paper insulation aging, but also has great effect on the dielectric properties of oil-paper insulation. In this paper, dielectric response and space charge behaviour of oil-paper insulation sample with three different moisture content were investigated using the frequency dielectric spectroscopy (FDS) and the pulsed electroacoustic (PEA) technique respectively. The influence of moisture on the dielectric response and space charge behaviour of oil impregnated paper insulation was analysed. Results show that moisture has much great effect on the FDS and space charge behaviour of oil impregnated paper insulation. In the range of 10-3~106Hz, the relative permittivity of oil impregnated paper increases with its moisture content increased. And in the range of 10-2~106Hz, the dielectric loss of oil impregnated paper also increases with its moisture content increasing. In addition, the higher the moisture concentration of the oil impregnated paper, the deeper the charge penetration into the insulation paper, and the larger quantity of hetero-charge was observed in the vicinity of positive electrode and homo-charge appears in the vicinity of negative electrode