Study of asymmetrical leakage currents of metal oxide surge arrester due to multiple current impulses

This paper presents the study of asymmetrical leakage current of metal oxide surge arrester (SA) after being tested with multiple current impulses. The study is made using 2 SAs specimens of 21 kV rated voltage, 5 kA nominal discharge current. The experiment is divided into 4 steps; 10 shots of positive discharge current impulses, reference voltage measurement, 5 shots of negative discharge current impulses and reference voltage measurement. Initial conditions of the SAs are assessed prior to the testing: temperature measurement, 1 mA reference voltage and resistive leakage current at rated voltage. Then, both specimens are applied current lightning impulses at 200% of rated discharge current (10 kA) and the temperature is measured after. The lightning current impulse is 8/20 µs waveform and the duration between each impulse is 10s. Prior to the application of multiple current impulses, the difference of resistive current peak amplitude of specimen 1 and 2 were 3% and 0.95% respectively. Following positive current lightning impulses, the value changed to be 71.245% and 72.75% respectively. The specimens were then left to cool down in the room temperature for 1 day. After application of negative current lighting impulses, difference of resistive leakage current of specimen 2 changed to be 1.99%, and specimen 1 broke down after 2 impulses. Asymmetrical leakage current phenomena caused by the impulse current may negatively affect the breakdown characteristic of the SA which should be relevant with the collected charge inside the SA material, however, the opposite polarity of the applied impulse currents may eliminate such problem.