Leakage Current and Discharge Phenomenon of Outdoor Insulators

Abstract: This paper descirbes leakage current characters and discharge phenomenon of outdoor insulators both in the lab and in the field. The results are hoped to be used for online monitoring of the contamination levels. The following contents are introduced in the paper: leakage current monitoring systems, relationships between leakage current and discharge phenomenon, flashover prediction methods and its applications in the field. The leakage current monitoring system is introduced firstly. Then the relationships between leakage current and discharge phenomenon for both suspension insulators and post insulators are presented based on the laboratory tests. A new parameter (I) that accounted for maximum leakage current (Ih) and different insulator shapes is introduced to estimate the flashover voltage for different kinds of pollutant layers when they are saturated with moisture. Meanwhile, the relationships between relative humdity (RH) and maximum leakage curren, altitude and maximum leakage current are investigated. With these results a flashover prediction method is developed. Ih measured in different relative humidity is converted to I for the same contaminate layer when it is saturated with moisture. Then the flashover voltage is estimated by I. Furthermore, an online leakage current monitoring results are analyzed. The relationships between leakage current characters in the field and ambient relative humidity are analyzed. The results show that although there are some differences between the leakage current in the field and in the lab because of some especially serve atmospheric conditions, the relationships are similar. Meanwhile, leakage current waveforms in different weather conditions are investigated. The waveforms of leakage current in the field are similar with those in the lab. The leakage current waveform that accounted for strong arc is found in the field. Finally, the contamination level of the field insulator is evaluated. The results corresponds well with the local condition.