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 a concern of 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 throughout 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 the paper. The mathematical model of a substation is implemented in the 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