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

Nowadays, plenty of sensitive electronic devices are installed in secondary circuits in substations. When lightning strikes a substation and transmission line, lightning currents flow into the grounding structure of the substation through shield wires and lightning surge arresters in the primary circuit, and lightning overvoltages are induced on control cables in the secondary circuit owing to the effect of transient ground potential rises of the grounding structure and electromagnetic coupling. Shielded control cables are one of the countermeasures against lightning overvoltage induced on control cables; thus, it is useful to evaluate the effectiveness of shielded control cables for designing protection measures properly. Recently, the finite-difference time-domain (FDTD) method, which is one of the full-wave numerical approaches, has been commonly used for simulating electromagnetic transient phenomena in grounding structures, such as the grounding grids of substations. In this work, first, we studied the modeling of tape-type shielded control cables used in substations for FDTD-based electromagnetic transient analyses. Then, using the control cable model, we simulated a test platform of primary and secondary circuits in a substation and calculated the transient response of a grounding grid and voltages induced on the control cable when a lightning impulse current was injected into the grounding grid. We then compared the calculated results with the measured waveforms for validation.