GB343667A - Improvements in or relating to control systems for electrical apparatus such as motors - Google Patents

Abstract

343,667. Protective cut-out arrangements. MANN, R. W., Langford, Cauldwell Lane, Markseaton, Northumberland, FERGUSON, F. G., 11, Moreton Avenue, Stretford, Manchester, GOWAN, S.,4,Wardle Road, Sale, Cheshire, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Bush House, Aldwych, London. Dec. 28, 1929, No. 39686. [Class 38 (v).] In switchgear arrangements for controlling motors for coal-cutting machinery in which a " gate-end " switch is controlled by a pilot switch at the motor, the pilot switch being operated conjointly with the reversing motor controlled, an auxiliary relay is provided, controlling contacts in a low-voltage pilot-and-earth protective circuit. The auxiliary relay contacts are moved into and latched in the position in which they short-circuit a resistance in this protective circuit when the controller is placed in the " off " position. When the controller is moved into the " on " position the line current causes attraction of the relay contact arm so that the resistance is included in the circuit of the main relay controlling the "gate-end" switch, the consequent reduction of current in this circuit serving to maintain this relay in its attracted position but being insufficient to attract it again if it is temporarily de-energized. As shown in Fig. 1, the circuit of the main relay 14 controlling the operation of the "gate-end" switch 5 is fed from a step-down transformer 15 the primary of which is connected between two phases by an auxiliary contact 18 of the main switch 7, this circuit being under the control of a leakage relay 16. The secondary circuit of transformer 15 passes through the pilot- and-earth circuits P, E and includes the coil 19 of the main relay 14, a thermal trip-relay 20, quickacting overload relay 21, thermal overload relay 22 and auxiliary relay 23. The latter as shown has contacts normally short-circuiting a resistance 25, so that when the reversing controller 3 is moved from the " off " position the main relay circuit is completed at contacts 24 shortly after the motor contacts 9 are brought into engagement, this circuit also passing directly through the auxiliary relay contacts. The main relay 19 by closing its contacts completes the circuit of the closing coil 13 for the "gate-end" switch 5. Shortly after the closing of the "gate-end" switch, the current in the coil 26 of the auxiliary relay attracts its armature and removes the -short-circuit from the resistance 25 which is thereby included in the circuit of relay 14. The reduced current in this relay is sufficient to maintain it in the attracted position, but if this circuit is broken as by the operation of a protective relay the current in the protective circuit is insufficient to re-close relay 14. In this case the controller has to be returned to the " off " position during which a cam (not shown) engages a projection 44, Fig. 2, attached to the armature of the auxiliary relay so bringing the insulated bridging contact plates 33 into engagement between the hemispherical contacts 35 carried by the spring blades 36, 37. The contacts are thus held in this position until a subsequent closing movement of the motor controller energizes the coil 26. The arrangement of the contact members 35 exerts a latching effect on the movable contact member, and this is augmented to. prevent the contacts being closed by vibration when in the position shown in Fig. 3 by roughening the contacts 35 at points 45. The coil 26 is mounted on a laminated core 27 the polepiece of which carries a shading ring 28 to prevent chattering.