GB620439A - Improvements in or relating to electrical overload protective systems - Google Patents

Abstract

620,439. Electromagnetic switches; protective cut-out systems. RUDD, C. H. Jan. 17, 1947, No. 1603. [Class 38(v)] In a protective system, each of a number of overload relays, located at successive points of a supply system to be protected, has a solenoid adapted to increase the operating time of the relay in response to a current transmitted over auxiliary contacts, which close immediately on an overload, of the relay succeeding it in the system, so that the relay nearest to the fault will operate before the others. In the application to a radial feeder 1 with a branch feeder 2, the current flowing from left to right, the auxiliary contacts A of the branch relay Rl nearest to the junction are in parallel with those of the relay R immediately to the right of the junction, either of the relays being able on fault to energize the coil S of the relay R immediately to the left of the junction, according as to whether the fault is in the branch 2 or the right-hand portion of the feeder 1. On a fault at F, on the branch, the contacts A, of the relays R to the left of the junction and those of relay R1 next to the junction, close to energize the coils S of the preceeding relays R, which operate after a time delay and only if the relay R1 next to the junction fails to clear the fault. The system may be applied to a radial feeder without a branch feeder, by the omission of the relays R1, Fig. 1, (not shown). The invention may be applied to a ring-main feeder with or without a branch feeder, Figs. 3 and 4 (not shown), by the use of directional and overload relays, wherein the contact device A of each relay comprises a contact which can selectively engage either of two fixed contacts, according to the direction of current flow, to increase the time-delay of the relay immediately to the left or right of the said relay. In the application to the protection of a number of feeders connected by a common bus-bar, Fig. 5, (not shown), one of the fixed contacts of each device A is replaced by a number of contacts equal to one less than the number of feeders and in series with the coils S of the other feeders, so that on a fault in one feeder, the time delays of the relays in the other feeders are increased. Electromagnetic relays.-The time setting devices, Fig. 6, may comprise quadrants Q which rotate on overload. thereby permitting contacts A to close. Each quadrant carries two adjustable members M, N, adapted selectively to actuate the tripping contacts T, according to whether the coil S is de-energized or energized. The contacts T are carried by the pivoted armature P of the coil S, so that when this is energized, the contacts T are moved into the path of the member N. In a modification, Figs. 8, 9 (not shown), members M, N of equal length are arranged on either side of the quadrant Q, the armature P and contacts T moving sideways when the coil S is energized.