Measurement and analysis of the conduction current of the oil-paper insulation under high DC electric field

The conduction mechanism under high field has a close relationship with the pre-breakdown process of dielectrics. In this paper, a conduction measuring system was built to explore the conduction mechanism of oil-paper insulation under high field. Based on the established system, the conduction current of transformer oil, kraft paper and oil impregnated paper were investigated under various applied fields. The finding shows that the conduction mechanism of transformer oil can be divided into three stages according to its behavior. Especially, at high field, the current flowing through the transformer oil appeared to proportional to the square of applied electric field. Therefore, the conduction mechanism of transformer oil was satisfied with space-charge limited current theory in high electric field. In addition, the apparent carrier mobility μ in transformer oil was 1.1×10
⁻⁹
m
²
/(V±s). As for oil impregnated paper, the obtained ln(I) and E
^1/2
characteristics behaved linearly, which could be explained by Schottky and Pullen-Frenkel mechanism; with the increase of aging time, the conduction current would decrease.