Characteristics of PD for reactor interturn insulation under pulse oscillating voltage

Pulse oscillation overvoltage arises during the switching process of dry-type air-core reactor. In order to evaluate the destructive effect of impulse oscillation overvoltage on turn-to-turn insulation, a high voltage experimental system of impulse oscillation is designed in this paper, and partial discharge test on inter-turn insulation samples with different sizes of air gap under high frequency oscillation pulse voltage are carried out. The initial partial discharge voltage and the development process of partial discharge are recorded also. Research results indicate that the air gap can significantly reduce the value of initial partial discharge voltage, and the value decrease slowly with the change of the air gap dimension. With the increase of the applied voltage´s time and the voltage amplitude, the partial discharge will develop quickly, making the sample´s breakdown voltage decline obviously. These rules could be explained by using the air gap´s maximum electric field, the corresponding field strength of the initial particle discharge is close to the breakdown field strength of air. The air gap´s partial discharge can adversely affect the insulating property of the reactors´ turn-to-turn, so the dry-type air-core electric reactor has to avoid air gaps as much as possible and corresponding protective measures should also be taken.