This presentation, given by Andrew Legro, PE. Field Application Engineer at ABB, first discusses the difference between a low voltage circuit breaker and a protective relay and associated components (breaker, CT, relay). With an understanding of the functionality, using an electromechnical 50/51 as a foundation, attendees learn where to apply various inverse time current curves and overcurrent relay elements (50,50D,51, definite time curve). The presentation then discusses the importance for matching the relay to the breaker and how withstand, trip/clearing time relate to the time current curve. Digital, multifunctional relays, provide multiple solutions in a single package and coordinate from relay to relay, relay to fuse, and relay to LV breaker.

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