Simulation for the Partial Discharge of Wedge-Shaped Oil-paper Insulated under DC Electric Field

The converter transformer is a kernel equipment in ultra-high voltage direct current(UHVDC), and some partial discharge(PD) occurs under wedge-shaped electrode of the converter transformer. For researching PD mechanism of oilpaper insulation at wedged electrode, a model based on the fluid dynamics theory and the bipolar charge transport theory was built. Microscopic images including PD and charge distribution obtained by this simulation were analyzed. Besides, the influence of parameters such as voltage amplitude and charge mobility on PD characteristics were discussed. Through the simulation, we can get the conclusion that the partial discharge process under DC stress at the wedged electrode can be broadly classified into the following parts: ionization and polarization in oil, the surface discharge at the oil-paper interface, the deep discharge in pressboard, and surface flashover. During the discharge process, the voltage plays a facilitating role in the discharge. And the effect of charge mobility especially of pressboard on discharge is twofold, the flashover voltage reaches the maximum when the electron and hole mobility is 10
^-13
m
²
V
⁻¹
s
⁻¹
, when the longitudinal trend of discharge is the strongest. The longitudinal trend inhibits the development of transverse discharge and increases the flashover voltage. The results of this paper have theoretical value for studying the partial discharge mechanism of converter transformer.