Reduction of interference on substation low voltage wiring

This paper describes test results and mitigation methods of electromagnetic interference @MI) on control and low voltage circuits in substations caused by air disconnect switch operation. The tests are focused on a comparison between unshielded and shielded circuits from capacitively coupled voltage transformers (CCVT) and other equipment circuits in the vicinity. New test data are presented comparing unshielded and shielded cables and transient currents on all connections to the CCVT including the pedestal and ground strap. The paper gives a practical and understandable explanation of the causes of EM1 in substations and how shielded cable and parallel ground conductors reduce interference. Design guidelines are listed in the Conclusion.