Grounding techniques and induced surge voltage on the control signal cables

Accurate operation of the metering, control and protective equipment in a substation relies on dependable input signals. The surge-induced voltage on the control signal cables during a transient is always of concern to electrical power engineers. However, due to limited space, there are many different kinds of circuits close to each other in an electric power substation. Any switching operation or lightning strike at a substation can cause serious transients with high-frequency oscillatory waveforms to spread through high-voltage circuits, which, in turn, may give rise to a transient electromagnetic field in the substation. If a signal control cable runs for some distance in parallel with high-voltage buses, a significant amount of voltage may be induced. The control, protection or measurement equipment connected in the low-voltage circuits, in turn, become exposed to these transients. A method of induced voltage calculation is presented in this paper. The mathematical model of a substation is implemented in the Electromagnetic Transients Program (EMTP) to study the induced voltage during transients. The simulation results are compared with field testing results. A recommended grounding practice with the support of computer simulation and field testing results is also included in this paper.