Circuit Breaker Failure Protection: A Logical Design Path

Circuit-breaker-failure protection is a widely discussed topic from requirements to implementation and testing. The general theory, while seemingly simple, quickly becomes quite complex. Fortunately, IEEE, NERC, and many others have provided numerous examples of circuit-breaker-failure implementation and the issues and suggestions that can arise. All of this information is substantial and can be overwhelming when choosing a design path. This paper presents a decision-based logic path that guides the reader from design constraints to the best-practice solution for their given case. This paper begins with design constraints including available fault current, circuit-breaker layout, and single-pole vs. three-pole tripping. Next is consideration of security, speed and other outlying conditions. Once this general design path has been determined, the next portion determines the features of the circuit-breaker-failure protection scheme; these include timing, re-trip, remote trip, single vs. dual trip coils, and alarming. Lastly, this paper presents a real design implementation with considerations of external circuit-breaker-failure initiate, internal vs. external tripping sources, blocking the circuit-breaker-failure protection, the utility of knife blades and cut-out switches, and more. A full design path is presented along with specific guidelines on the needs and implementation of that design.