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 distributingsubstation 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.

Incorporating the LEMP Impact on Lightning Surge Analysis of Transmission Lines in EMT Simulators

“…Pursuing simplicity, the tower grounding was modeled using a constant resistance Rgr, and the FD characteristics were not considered. Note that the FD characteristic of the tower grounding is inherently considered in the FDTD method [66], [67], and this characteristic may cause the difference in analysis results for high-soil-resistivity cases, as shown in Sect. IV.C.…”

Three-Dimensional FDTD-Based Simulation of Lightning-Induced Surges in Secondary Circuits With Shielded Control Cables Over Grounding Grids in Substations

“…14 shows an analysis space used to simulate the experimental setup in the FDTD method. The dimensions of the analysis space were 330 m × 380 m × 300 m, where the bottom space with a thickness of 150 m was treated as soil, and the relative permittivity of the soil was set to 30 [40]. Absorbing boundaries based on Liao's formulation of the second order were applied to all the external surfaces to assume an open space [66].…”

“…In previous studies regarding the application of the FDTD method to the lightning transient analysis of substations, the main focus was put on the analysis of lightning transients entering substations owing to lightning strikes and of the transient responses of grounding structures (e.g., [31], [37], [38], [39], and [40]). Such lightning transients propagate in the primary circuits and the grounding structure of substations, and then electromagnetic disturbances are induced in the secondary circuits through the effect of surge transitions from the primary to secondary circuits at instrument transformers such as VTs and CTs, the effect of transient ground potential rises (GPRs) of the grounding structure and electromagnetic coupling due to the lightning currents propagating through the grounding structure, the effect of direct coupling from the lightning transients propagating through the primary circuits, and so forth [20].…”

Applying FDTD Simulation to Lightning Surge Route Analysis in Microwave Relay Stations

“…Recently, a method for directly solving Maxwell's equations has often been used for calculations in which it is difficult to apply the conventional methods based on circuit theory, such as surge analysis of three-dimensional structures. Among them, the finite difference time domain (FDTD) method [2] can easily deal with conductors and dielectrics, and is applied to surge analysis in many fields such as voltage calculation across arcing horns of transmission line towers [3,4], transient response analysis of a ground electrode [5], and calculation of induced voltages on a control line by current flowing through a grounding grid [6]. This report shows the results of studying the branch aspect of a lightning surge current in an actual microwave relay station and the applicability of the FDTD method for studying lightning protection measures.…”