Simulation and Analysis of Corona Discharge in Insulating Oil from Power Frequency to Very Low Frequency

Partial discharge (PD) diagnostic tests plays an important role on condition monitoring and fault diagnosis of power equipment insulation. With the very low frequency (VLF) diagnostic test widely used in the power system, the power capacity can be remarkably reduced by lowering the applied frequency. However, simulating the corona discharge process in insulating oil from power frequency to very low frequency is difficult because the corona discharge process in insulating oil at different frequencies takes much longer than a single corona discharge in insulating oil. Therefore, it is necessary to establish the simulation and experiment of corona discharge in insulating oil from power frequency to very low frequency for this problem. A simulation model of corona discharge in insulating oil from power frequency to very low frequency based on the finite element method is proposed in this paper, in which needle-plate electrode model based on CIGRE Method II was selected. Then making the dielectric constant of materials at frequencies from 50 Hz to 0.1 Hz was measured from experiments as parameter variable. Finally, with simulation model based on the Poisson equation and hydrodynamic continuity equations performed in COMSOL Multiphysics, the current intensity, the distribution of electric field intensity, and the development of streamer in corona discharge in insulating oil were analyzed. According to the simulation results, with the decrease of frequency, the electric field in insulating oil increased slightly at first and then decreased sharply. Simulation results were in good agreement with experiments, in which the maximum discharge, average discharge, and pulse repetition rate decreased significantly at low frequencies. This paper shows the characteristics of corona discharge in insulating oil from power frequency to very low frequency by simulation and experiment, providing the reference for insulation diagnosis of power equipment with PD test at very low frequency and studying the mechanism of frequency effect on corona discharge.