GB1250810A - - Google Patents

Abstract

1,250,810. Electromagnetic relays. SOUTH LONDON ELECTRICAL EQUIPMENT CO. Ltd. 21 Nov., 1969 [22 Nov., 1968; 27 March, 1969], Nos. 55565/68 and 16140/69. Heading H1N. [Also in Division H2] An overload protective arrangement comprises an electromagnetic relay with a magnetic circuit 13, 14 embracing a conductor, e.g. a busbar 10, and including a core 15, an armature 16 and first contacts 19. A main magnetic shunt 20 and a calibrating magnetic shunt 21 are associated with a magnetic reed contact unit 23 (not shown in Fig. 1) positioned at right angles to the direction of current flow in the conductor. A metallic slug 25 is provided round the core 15 to delay the rise of the field so that the first relay contacts will not be operated within one half cycle of the A.C. current in the conductor. The first contacts 19 are connected in a protective circuit, e.g. for circuit-breaker tripping and an alarm. The reed contacts 23 are connected in a high-speed lock-in arrangement of a protective circuit comprising a silicon controlled rectifier SCR, resistors R1, R2 and a capacitor C1. The resistor R2 and the capacitor C1 preventing the firing of the rectifier in response to transient voltage conditions. The contacts 19 may be connected in parallel with the contacts 23 and the arrangement is stated to provide for response to a D.C. component as well as high-speed response to A.C. overload. In a modification, Fig. 4 (not shown), the main shunt is a first tube housing the contact unit and having a central cut-out portion. The calibrating shunt is a second tube movable on the outside of the first tube so as to cover the cut-out portion to a greater or lesser extent.