Negative DC corona characteristics in SF₆ under moisturecontamination

摘要

This paper reports on the effect of moisture contamination relatedto negative partial-discharge activity in SF₆. Moisturecontamination is common in gas-insulated systems and is mainly due to 1)temperature-dependent water desorption from inner surfaces and 2)external sources of pollution that infiltrate during installation andoperation of the apparatus. However, few studies have been published onthe subject and even they have focused on positive or AC voltages.Little is known about the influence of water vapor on negativepartial-discharge phenomena, or its physical reality. The aim of thiswork, therefore, is to identify the influence of water contamination ona negative partial-discharge regime from electrical measurements and tocorroborate our observations with known data. Any observations ofnegative effects from water contamination and/or methods of detectingwater contamination by means of electrical measurements on gas-insulatedsystems could be of great help to engineers. The experiment wasconducted under true-corona conditions; for that particular arrangement,the breakdown occurred in the range of 25 kV for atmospheric SF₆. The characterization study focused mainly on the corona currentand the distribution of recorded pulse amplitudes and frequencies. Thebreakdown and inception voltages were also measured. The results of allthese measurements, taken separately in pure and contaminated SF₆ are compared