Methods for Reducing Induced Voltages in Secondary Circuits

The protection of control and instrumentation cables in a high-voltage switchyard is becoming more essential as higher magnitudes of system voltage, load and fault currents, or overall power levels are handled. Concurrently with these increases in transient severity in the switchyard, a greater need is developing for more sophisticated control involving components more easily damaged by induced voltages. When the problem is recognized early enough so that proper circuit configurations and metallic sheaths can be incorporated into the initial installation, it can be solved quite effectively. Two criteria developed for control circuit protection are radial circuits where all conductors are contained within one cable (no large loops formed), and conductive sheaths of low resistance connected to the grounding grid at both ends.