Effect of Moisture on Electrical Properties of Epoxy/Paper Composites

Epoxy/paper composites are main insulating component of high-voltage dry-type bushings. In order to study the effect of moisture on electrical properties of epoxy/paper composites, the neat epoxy resin and epoxy/paper composite samples with or without water were prepared by using a vacuum casting and curing system. The water content was controlled by mixing water with epoxy pre-polymer and curing agent in a certain proportion during the curing processes. The glass transition temperature (T
_g
), real part of permittivity (ε'), imaginary part of permittivity (ε"), space charge distribution and AC electrical breakdown strength of samples with or without additional water were measured. The experimental results show that the increase of water content results in the decrease of T
_g
and breakdown strength of the composites. Also, the ε', ε" and space charge density increase with the addition of water. The absorbed moisture brings about impurities and hydroxyl groups which reduces the activation energy of polarization, and increases the trap density of the sample, making it easier to capture charges, and further affects the electrical properties of epoxy/paper composites.