Study on the electrical equivalent circuit models of polluted outdoor insulators

During operation, an outdoor high voltage insulator may come under various stresses. One of them is environmental pollution, where pollutants stick to the insulator surface. The polluted condition may produce leakage currents or even electrical discharges. Their waveforms are normally non-pure sinusoidal. To understand the correlation between insulator condition and its leakage current phenomenon, we will, in this study, investigate various equivalent circuits for representing insulator under different conditions. This paper presents the proposed equivalent circuit models of three main conditions of insulator, i.e. clean, polluted and polluted with dry-band discharge. In general, the model consists of capacitor(s) and nonlinear resistor(s). By using the models, the leakage current simulations have been done using ATP/EMTP software package. The simulations, show that a clean low capacitance insulator yielded a pure sinusoidal current waveform, whereas that of a high capacitance yielded an oscillating sinusoidal current waveform. On the other hand, the polluted insulator simulations produced distorted sinusoidal current waveforms. At the end, the polluted insulator with dry-band discharge simulations showed chopped sinusoidal current waveforms. It was also showed the harmonic ampitudes, where third harmonics were usually the second highest amplitudes, a part of the fundamental ones.