Abstract
For the practical insulation design of high temperature superconducting power apparatus, it is necessary to elucidate partial discharge (PD) inception characteristics in liquid nitrogen (LN2). However, most of investigations have been limited to breakdown characteristics in LN2. Furthermore, the influence of thermal bubbles on PD inception characteristics should also be taken into account.
In this paper, we investigated PD inception characteristics in LN2/solid composite insulation system under practical operating conditions with thermal bubbles. Especially, we focused on V-t characteristics for PD inception under different bubble conditions. Experimental results revealed that (1) PD inception voltage was mainly influenced by the gas density in thermal bubbles, and mutually affected by the volume rate of thermal bubbles in the gap space. (2) n value of V-t characteristics for PD inception was 86-106 under small thermal bubble disturbance, while 38-54 undr large disturbance. (3)Pressurization of LN2 largely contributed to the enhancement of PD inception voltage, while little influenced on the n value of V-t characteristics for PD inception.
