Traditional overcurrent relays (50/51) used an induction disk for the time delayed element (51) and a solenoid for the instantaneous element (50). Letters are sometimes added to specify the application (IEEE Standard C37. ANSI IEEE Standard Device Numbers are below: (the more commonly used ones are in bold) 86T is a Lockout Relay for a. What is the function of power system protection? For what purpose is IEEE device 52 used? Why are seal-in and 52a contacts used in the dc control scheme? In a typical feeder OC protection scheme, what does the residual relay measure? Electromechanical Reset? (Y/N) Const. Response NOT. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected.
