Patent GB-550722-A (GB)
Title: Improvements in and relating to electric motor control systems
IPC: B60L15/04
Filed: 1941-07-14
Abstract: 550,722. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. July 14, 1941, No. 8910. Convention date, July 13, 1940. [Class 38 (iii)] A series-parallel control of motors 10, 11, 12 and 13 gives constant current acceleration, the current value being selected by the driver in the parellel position, and constant current dynamic braking combined with application of air brakes. An air operating motor 28 of the type described in Specification 514,263 adjusts the starting resistors 65, 67. Preparing the motor circuit. Reverser 14 is closed and master 15 and brake 16 controllers placed in " off " positon. Circuits through contacts 33 on master 15 cause braking contactor B to lift thereby connecting motors in parallel braking loops as shown in Fig. 2, a flashing circuit for the fields 46, 47, to be made at contacts FF and the air motor to move brushes on resistors 65, 67 to position B. First series position. The master 15 is moved to its first position and the brake 16 to its " Run and Coast " position. The brake contactor B drops and the air motor 28 moves the brushes quickly to full resistance position A, thereafter contactor LB1 lifts, followed by LB2. The motors are now in series with resistors 65, 67, and 74. Full series position. Master 15 is moved to its second position. Coils 27 and 31 are energized to cause air motor to move resistor brushes from A towards B. Current relay CLR vibrates so as to adjust average energization of coil 27 to allow brushes to move at a rate to give constant accelerating current. Parallel position. Master 15 is moved to any of the four parallel positions. Contactor PSG lifts to give a "bridge" transition and coil, 31 de-energized to reverse air motor 28. Brushes move back from B to A cutting out resistance again under control of relay CLR and coil 27. The four parallel positions of master 16 select different rates of acceleration by varying resistor 115 in circuit with aiding coil 97a on relay CLR, also cams 107 and 117 driven by the air motor cause contactor PSG to pick up before brushes reach positions B if the higher rates of acceleration are set by the master 16. Coasting. Controller 15 is returned to "off" position. The motor circuit is returned to the " preparing state, but relay BR vibrates to cause air motor 28 to adjust the resistors 65, 67 to a high value at which the dynamic braking current is ineffective to prevent coasting. If current is excessive relay BR picks right up to energize relay AR thus allowing contactor C to drop and insert resistance 74. Braking. Controller 16 is moved to " Dynhold " position. Contactor C lifts to exclude resistor 74 from the braking circuit. and ballast loops 142 are inserted in series with operating coil of relay BR so that this relav causes air motor 28 to move resistor brushes from A to B to give constant braking current. If controller 16 is moved to a " service " position valve 76a is opened to give air braking and diaphragm) 144 increases tension on spring of relay BR so as to increase dynamic braking current. Other features. "By - Pass" contacts on master 15 allow increased motoring current to give acceleration when starting up a stiff incline. Push-button 24 stops acceleration when required, e.g. to correct wheel slip. And relay OLR cuts out the circuit of contactor LB1 on overload and locks up on its winding 148 until controller 16 is returned to "off."