Diagnostics of outdoor insulators using leakage current waveform parameters

This paper reports the investigation results on the leakage currents (LC) on the ceramic as well as polymeric outdoor insulators. The LC waveforms were measured under various environmental conditions (humidity and pollution). The LC waveform parameters such as magnitude and harmonic content (as indicated by the total harmonic content (THD)) were analyzed. 3rd, 5th and 7th harmonics and higher odd harmonics were observed for symmetrical-distorted LC waveforms while for unsymmetrical-distorted LC waveforms, odd and even harmonics were observed. The results also showed that in general the magnitude of LC was good enough to show the condition of the insulators. However, under discharge condition (for example as a result of dry band arching) the LC magnitude should be combined by the THD to show a better correlation with the insulator condition. The product between THD and LC magnitude may be used as a diagnostic parameter.