GB607194A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

607,194. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 8, 1943, No. 405. Convention date, Jan. 14, 1942. [Class 38 (iii)] A hoist motor 13, with a series field 13a, is stopped at the upper limit by dynamic and mechanical braking; is reversed out of the limit with a resistor in shunt to the armature so as to give a shunt characteristic; and outside the limit is run in the lowering direction as a shunt motor. A drum controller, Fig. 1 (not shown), has an " off," five " hoisting " and five '' lowering positions, and controls the various contactors in the motor circuit. A limit switch operated by the crane hook opens contacts 31, 32 and closes contacts 33, 34 at the upper limit of hoist. The motor, a braking resistor 65 ; the limit switch and a brake release coil 19 are mounted on a movable trolley and are connected through five trolley connections 36, 37, 38, 39 and 45 to the rest of the equipment on a fixed panel. Hoisting.-Contactors 16, 47, 48, 49 and 54 are closed in all positions and 24 opens to interrupt emergency braking circuit through resistor 25. Contactor 41 is closed in first and second positions to shunt resistor 43 across armature 13 so as to give an anti-coasting feature if controller is turned from high to low speed whilst raising an empty hook. Contactor 61 closes in the second; 41 opens in the third; 28 closes in the fourth and 29 closes in the fifth position. Over hoist.-Limit switch contacts 31, 32, 33, 34 interrupt motoring circuit and complete braking circuit through resistor 65, and also de-energizes coil 19 so that mechanical brake sets and prevents the hook oscillating out of and into the limit. Lowering out of limit.-Contactors 17, 47, 48, 49 and 54 are closed, thereby energizing motor with its series field for lowering, resistor 65 is without effect as it is in shunt to the armature 13 and field 13a. Relay 40 picks up as it is now connected across the whole of the motor and causes contactor 41 to close and place resistor 43 in shunt to the armature, thus giving a shunt characteristic and stability in lowering. In the second and third positions contactors 24 and 47 open. As the hook passes out of the limit, contacts 31, 32 reclose and 33, 34 reopen, the motor is now connected as a shunt machine. Relay 40 opens and consequently contactor 41 opens. Fourth and fifth positions of the controller now become operative and acceleration is continued by the sequence of 48 opening; 61, 28 and 29 closing; and finally 49 opening.