Partial Discharge Inception Characteristics under Thermal Bubble Condition in Composite Insulation System of Liquid Nitrogen and FRP

Abstract

We investigated partial discharge (PD) inception characteristics in composite insulation system of liquid nitrogen (LN2) and FRP with uniform electric field under thermal bubble condition. Experimental results revealed that PD inception field strength (PDIE) decreased as the bubble rate increased, and finally reduced down to the range of the breakdown strength in nitrogen gas. Moreover, we measured PD signal and observed the behavior of thermal bubbles. It was clarified that PD took place in thermal bubbles and the PD charge had close relationship to the size of thermal bubbles.