Simulation of transient earth voltages aroused by partial discharge in switchgears

Switchgears are the key equipments in the distribution network. Operating switchgear with active Partial Discharge (PD) increases the risk of failure occurring at the time of switching leading to increased risk to the operator. PD in switchgears can be considered to take two forms, surface discharge and internal discharge, if allowed to continue, eventually causes the insulation to break down catastrophically. The electromagnetic pulses produced by PD are in large part conducted away by the surrounding metalwork but a small proportion impinges onto the inner surface of the casing. These charges escape through joints in the metalwork, or a gasket on a gas insulated switch, and pass, as local raised voltages, across the surface of the switch to earth. These pulses of charge were named by Transient Earth Voltages (TEV), and the level of these TEV signals are proportional to the condition of the insulation for switchgear of the same type and model, measured at the same point. So TEV is a very powerful comparative technique for noninvasively checking the condition of switches. In this paper, the Finite-Difference Time-Domain (FDTD) method was employed to simulate the propagation law of TEV in the switchgear. The simulation results show that, the TEV amplitude is proportional to the PD pulse amplitude, increases with PD pulse width decrease and decrease with the distance between detection point and PD source.