Analysis of leakage current wave forms for field-aged and new composite insulators

Results of measurements and analyses of leakage current (LC) patterns on field-aged and non-aged insulators are presented. The field-aged insulators were exposed to marine and industrial pollutions as well as to tropical weather conditions for one year. The LC measurements were performed on them under natural and artificial contaminated conditions. The non-aged insulators were previously used for pollution testing. In most cases, the LC patterns on the field-aged insulators were sinusoidal in shape whereas they were highly deformed on the non-aged insulators. These different LC patterns were quantitatively analysed by means of a circuit model representing a polluted and wet insulator surface. A modification of the previously developed neural network for evaluation of the third and fifth harmonic contents of the LC patterns is also presented.