Electrical equivalent circuits of outdoor insulators based on leakage current waveforms and computer simulation

During operation, outdoor insulators may severe a certain degree of pollution which may reduce their performances such as surface resistance and flash over voltages. Under these conditions a large leakage current (LC) may flow on the surface and degradation may take place. The LC waveforms are normally non-pure sinusoidal. This is due to the non linear behavior of insulator surface and in particular condition electrical discharges ma take place which distort the leakage current waveform. In order to understand the behavior of the leakage current on the outdoor insulators, computer simulation of the leakage current was done by utilizing electrical equivalent circuits using ATP/EMTP. The simulated leakage currents were compared with those obtained from experiment. The similarity of the simulated and experimental leakage currents was indicated in the magnitude, dominant harmonic components, total harmonic distortion (THD) and asymmetry of the LC. The simulation results indicated good similarity between leakage current waveforms obtained from experiments and simulation. In general, the proposed equivalent electrical circuit consists of capacitor(s), nonlinear resistor(s), and arc model(s). These three parameters will be used to simulate the LC waveforms of ceramic insulator under various environmental conditions. Using the proposed equivalent electrical circuit, the influence of each electrical circuit components to the LC waveform characteristics, such as its magnitude, electric sparks, asymmetrical waveforms, and its total harmonic distortion (THD) is discussed.