Leakage current harmonic components: Indexes to insulator ageing

This paper reports an investigation carried out in the laboratory on 45 units of glass insulator samples. The insulator units comprise of 5 groups; new and field-aged insulators with different ageing period (>30, 20, 15 and <10 years) from 132 kV transmission line. The results revealed a correlation between the ratio of the 3^rd and 5^th harmonic amplitudes with the degree of degradation of the field-aged insulators. This correlation was validated with Dissipation factor (tan ¿) tests and flashover voltage measurements carried out on the insulators. All the results were in good agreement. Thus this finding suggests the viability of monitoring and diagnosing ageing insulators in situ.