A Study on Induced Voltages on an Aerial Wire due to a Current Flowing through a Grounding Grid

Abstract

The operating voltages of low-voltage control circuits in power plants and substations have become lower owing to the installation of digital-control equipment. This significantly increases the risk of faults and malfunctions of such circuits due to abnormal voltages in the control circuits induced by lightning and switching surges. Therefore, the prediction of the induced voltages is strongly required for protecting such circuits from abnormal voltages.Recently, the FDTD (Finite Difference Time Domain) method, which solves Maxwell's equations numerically, is applied to the simulation of surge phenomena on conductors placed in three-dimensional arrangements such as transmission towers and buildings. The FDTD method can easily take into account the finite conductivity and relative permittivity of the ground soil and ground structure in detail. These parameters affect the induced voltages on control circuits.In this paper, first, we perform the FDTD calculations for a grounding grid whose size corresponds to a distributing-substation area. Second, we calculate the potential rises of the grounding grid, currents flowing through the grounding grid, and induced voltages on a control wire above the grid. Comparing the calculated results with the measured ones, we confirm the applicability of the FDTD method to the calculation of the induced voltages on the control wire generated by current flowing into the grounding grid.