Patent GB-451133-A (GB)
Title: Improvements in or relating to emergency braking means for electric winders
IPC: B66B1/12
Filed: 1935-04-30
Abstract: 451,133. Master control of D.C. motors. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and COATES, H. J., c/o General Electric Co., Ltd., Witton, Birmingham. April 30, 1935, No. 12869. [Class 38 (iii)] Varying E.M.F. ; regenerative braking.- In a D.C. electric winder equipment with speed control by variation of generator field excitation and with emergency braking, operation of an emergency device effects the gradual application of mechanical brakes and the initiation of electric braking automatically regulated by progressive variation of field excitation. The generator and motor field windings 1, 2 and the control circuits are energized from a compound wound exciter 3 with shunt and series fields 4, 5, and the control of the driving motor (not shown), is effected by a controller 6 which controls a reversing field rheostat 7. The coil 22 of an emergency brake contactor 23 is in series with the normally closed contacts 24 ... 38 of various emergency relays or devices, and with controller contacts 39 and hand brake contacts 40. The coil 22 and the parallel-connected coil 41 of an excitation contactor 42 are energized through the contacts 39 when the controller 6 is in its off position. On closing, the contactor 23 opens contacts 43 to cut out the contacts 39, 40 from the circuit of the coil 22, and closes a maintaining circuit for the coil through contacts 44. It also closes contacts 46, 47, of which the former energizes the emergency brake solenoid 49 and causes the brake to be removed. When the contactor 23 opens, the solenoid is de-energized and the brake is gradually applied. When the excitation contactor 42 closes, its energization circuit is opened at contact 50, and a holding circuit for the coil 41 is closed through contact 56 and the contact 47 of the brake contactor 23. A parallel holding circuit is maintained through the contacts 58 of a spring-biassed motor voltage relay, the coil 59 of which is connected across the motor armature, and the contacts 58 of which are adapted to open when the armature voltage falls below a predetermined amount. The closing of the contactor 42 also short-circuits a resistance 60 connected between the exciter 3 and the generator field rheostat, and energizes the controller 6 through a contact 62. When the contactor 42 opens, the shunt field winding 4 of the exciter is short-circuited through contacts 64 of the contactor and through contacts 65, 66 of a hand-operated resetting switch 67. By moving the latter to its alternative position, the field 4 is connected across the exciter armature 3 and the resistance 60 is short-circuited, thus rendering it possible to obtain the requisite energization of the control circuits to effect reclosing of the contactors after an emergency braking operation. A further contact 68 of the switch 67, in the alternative position of the latter, effects the energization of an auxiliary coil 69 of a weak field relay whose contacts 36 constitute one of the series of emergency contacts. This relay is provided with a winding 70 in series with the motor field 2, and the coil 69 ensures closure of the contacts 34 on starting. The field 2 is connected in series with a resistance 72 adapted to be shortcircuited by contacts of a contactor 73 which is effective in the off and initial positions of the controller 6. The resistance 91 of the generator field rheostat 7 is connected through four steps 77 .. 80 of field resistance which are normally short-circuited by contactors 81 ... 84. The generator field winding 1 is connected to the resistance 91 by two contactors 87, 88, whose coils are energized when the controller 6 is energized and in an operative position, but when the controller is de-energized or in its " off " position the winding 1 is connected in a " suicide " circuit in series with a resistance 92 across the generator armature. When the brake contactor opens, a contact 48 energizes in parallel the coil of the contactor 81 and the coils 96, 97 of two time relay relays 54, 55. The contactor 81 thereupon opens, and excitation of the field 1 is weakened and electric braking commences. Contacts on the two relays 54, 55, which are duplicated as a safety measure, close in succession to energize the contactors 82 ... 84 ; finally, the last contacts 52, 53 of the relays open to de-energize the excitation contactor 42 with consequent deenergization of the controller 6 and the connection of the field winding 1 in its " suicide " circuit. The mechanical brakes, which were set in operation by the opening of the brake contactor 23, become fully effective about the time the contactor 42 opens. In a modification, voltage relays are substituted for the resistance relays 81 ... 84, and in another arrangement the voltage relay across the motor armature is replaced by a low pressure relay on the underside of the brake engine.