Analysis of Partial Discharge Characteristics at Cryogenic Temperature below 77K

77K 이하 극저온 상에서의 부분방전 특성 분석

Partial discharge measurement is one of the effective diagnostic techniques to predict abnormal high voltage dielectric insulation conditions of the electric equipments. Recently partial discharge diagnostic techniques were also utilized to evaluate the cryogenic dielectric insulation of high temperature superconducting electric equipment in liquid nitrogen. Generally, liquid nitrogen at 77 K is used used as the cryogenic and dielectric media for many high temperature superconducting high voltage applications. When a quench in the superconductor occurs, bubbles are generated which can affect the dielectric properties of the liquid nitrogen. So in order to reduce the bubble formation, subcooled nitrogen was also employed for this purpose. In this work, investigation of partial discharge characteristics of subcooled liquid nitrogen were conducted in order to clarify the retardation of partial discharge initiation voltage according to the different subcooling temperature of liquid nitrogen. And also the relation of partial discharge phenomena and the activities of bubbles were analyzed. It was observed that PD inception voltages shows rather different characteristics according to the decrease of subcooling temperature and the activities of bubbles were strongly influenced by temperature of the subcooled liquid nitrogen.