Influence of Nonlinear Processes in Soils on the Impulse Resistance of Grounding Electrodes

The article presents the results of laboratory studies of nonlinear processes during the flow of pulsed currents into moistened soil from electrodes modelling grounding devices of electric power facilities. A methodology for studying the pulse parameters of grounding devices has been developed and a laboratory stand and a generator measuring system have been developed on which these investigation were performed. The experiments were carried out on three types of electrodes at voltages of 20 - 50 kV and pulse durations from units to hundreds of microseconds. The article presents the combined results of optical and oscillographic studies. It is shown that the cause of the formation of spark channels during the nonlinear spreading of the pulsed current in the soil, when there is a sharp decrease in the grounding resistance, is the ionization-overheating instability that occurs when the current density on the electrode is greater than the critical one. The development of instability leads to an inhomogeneous current distribution and the appearance of spark channels. On the basis of experimental data, the current-voltage characteristics of the electrodes are obtained.