Designation of an Indicator for flashover prediction of porcelain and glass insulators based on experimental tests.

Flashover of polluted insulators in contaminated areas is one of the most important factors influencing the operation of transmission and distribution lines and finally line outages. Therefore, it is essential to prevent and detect flashover in the insulators. Hence, utilizing the insulator status monitoring systems and predicting their functions have absorbed a lot of attention over the recent years. In this paper, a new method is proposed for flashover prediction in porcelain and glass insulators. In this regard, a variety of experiments has been conducted on different types of insulators under different environmental conditions and analysis of their leakage current harmonics have been investigated. Fast Fourier Transform (FFT) analysis applied to the saved leakage current waveforms shows a strong correlation between the ratio of the third to fifth harmonic amplitudes by regarding the occurrence of critical conditions and degree of insulator ageing. Then, the third to fifth harmonic ratio of the leakage current (R3/5) has been proposed as an indicator of critical conditions in porcelain and glass insulators. The results of these experiments show that the mentioned harmonic ratio has a definite and constant procedure against the changes in the type of pollution and humidity rate. The results of experiments have indicated that increasing the index R3/5 to more than one represents a critical condition in the insulators and estimates a high probability of flashover. Also in whole the tests, value of the total harmonic distortion (THD) and flashover voltage are measured.