Generally, MV and HV circuit breakers do not contain relays, trip units, or any element that will automatically cause the breaker to operate. Virtually any manufacturer / model relay can be used with any manufacturer. Protective Relays - Technical Seminar Nov 2016 - Copyright: IEEE 2 Abstract: Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system. Selectivity is a mandatory requirement for all protection, but the importance of it depends on the application. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. Underfrequency load shedding (UFLS) is a protection system that senses when frequency is lower than acceptable and directly acts to shed load to correct the frequency drop. First, relays were used as signal repeaters within long-distance.
[PDF Version]