A method for unambiguous identification of on-field recorded insulator leakage current waveforms portraying electrical activity on the surface

The measurement of insulator leakage current in the field is necessary to have a better understanding of the electrical phenomena on the insulator surface. Since this electrical activity cannot be anticipated in advance, long term monitoring and storage of actual waveforms is necessary. This leads to significant accumulation of data. The presence of field noise in leakage current measurement further aggravates the problem of data size. The storage of noisy waveforms consumes available storage space without adding any significant information regarding the insulator condition. Therefore, it must be ensured that only the on-field recorded waveforms which reflect significant electrical activity on the surface are recorded. In this paper, the authors have proposed the use of Short- Time Modified Hilbert Transform (STMHT) to enhance the local characteristics of the field-recorded waveforms. It has been shown that the magnitude of the STMHT of a waveform at any instant has a good correlation with the slope of the waveform at that instant. Using this property, the proposed method is able to segregate the different types of field noise from waveforms portraying significant electrical activity. It is expected that this paper will contribute to the development of efficient devices for field monitoring of insulators.