GB784403A - Improvements in or relating to control systems for circuits including electromagnets - Google Patents

Abstract

784,403. Control systems for electromagnets. IGRANIC ELECTRIC CO., Ltd. Sept. 22, 1954 [Oct. 23, 1953], No. 27385/54. Class 38 (4). To increase the rate of build up of current in the coil 1 of a lifting magnet M supplied from a D.C. generator 24, 24a over a contactor 2 controlled by a switch 3, the circuit of the coil includes a current transformer 23, the voltage induced the secondary winding of which, whilst the current in the coil is building up, being injected over the potentiometer R4 into the field circuit of the generator to cause the generator to operate at increased voltage during this period. A rectifier 26 renders the transformer ineffective during switching off of the magnet. Upon closure of switch 3, contactor 2 responds, completing the circuit of the magnet winding over contacts 5, 6 and simultaneously operating (by an interlock 12) a further contactor 4 which then holds itself in over a circuit including resistors R1, R2. To release the load carried by the magnet, switch 3 is opened, whereupon contactor 2 drops out, opens the energizing circuit of the magnet winding at contacts 5, 6 and completes a reverse energizing circuit therefor over contacts 7, 8 of contactor 2 and contacts 9, 10 of contactor 4. The reverse current build up eventually causes contactor 4 to drop out and disconnect the magnet from the supply at about the time it becomes demagnetized. A discharge resistor R3 is provided to safeguard the magnet in event of failure of either of the resistors R1, R2. In a modified arrangement the voltage obtained from the transformer 23 is applied directly across the generator field 24a. Alternatively, the machine 24 may have fixed excitation and be in series with a booster machine which is excited from the transformer.