Case studies: Designing protection systems that minimize potential hidden failures

Historical data indicate that protection system hidden failures contribute to cascading power system disturbances. There are many types of hidden failures in protection systems, including in instrument transformers, primary equipment such as breakers, secondary system hardware and firmware, and relay settings. Most of the hidden failures can be traced to protection system maintenance issues. With advanced digital relays and communications, protection systems can be designed with much improved mechanisms that monitor protection system conditions and minimize potential hidden failures. This paper analyzes the key requirements of condition-based maintenance for protection systems. The paper proposes a relay supervisory system (RSS) as a part of protection systems to improve condition-based maintenance and mitigate hidden failures. The paper illustrates the structure and functions of the RSS with several real-world projects.