Open-circuited CT misoperation and investigation

A wire crimping error caused a current transformer (CT) to become open-circuited under load, a relay to operate, and an industrial plant outage. The wiring error was corrected, and the relay, internally damaged by severe overvoltage, was put back into service. Root cause analysis predicted and exposed the damage and led to corrective actions. This paper revisits the IEEE dielectric strength standard, safe design and work procedures regarding CTs, and what happens when a CT is open-circuited under load. The case study emphasizes the critical importance of commissioning tests and root cause analysis to power system reliability.