Patent GB-654375-A (GB)
Title: Improvements in or relating to dynamic braking control for electric motors
IPC: H02P3/06
Filed: 1947-08-27
Abstract: 654,375. Control of D.C. motors. IGRANIC ELECTRIC CO., Ltd. Aug. 27, 1947, No. 23699. Convention date, Aug. 28, 1946. [Class 38(iii)] A control system comprises an electric motor having a series field winding, means to connect the motor to a power circuit and to control the direction of flow of current through the motor armature to reverse operations of the motor, a suitably driven exciter having a source of exciting current other than the power circuit, and switch means whereby the motor field winding is connectable across the armature of the exciter when the motor is rotating without power from the power circuit and to establish dynamic braking connections for the  motor armature regardless of the direction of rotation. The system of Fig. 1 comprises two series motors having armatures A, A<SP>1</SP> and field windings F, F<SP>1</SP>. A master controller MS provides operation in a conventional manner, movement of this member regulating switches for connecting each motor to the supplylines, reversing the armature connections, and varying the resistances in the armature circuits during the acceleration period. A plugging switch having an operating-winding P and restraining- winding 2P is provided. The resistanceswitches have time-controlled restraining windings. After forward or reverse operation of the motors, movement of the master controller to the " off " position disconnects the motors from the supply and de-energizes relay-coils 1DF and 2DF, so closing contacts 1DF1 and 2DF1 and connecting the motor field windings in series with an exciter E. The exciter may be driven by the motors and is adapted to energize the motor field windings in the same direction as that obtaining during normal operation. Relay-windings 1AS and 2AS are also de-energized to close contacts 1AS1 and 2AS1. An excited field winding f is connected in series with a resistor r across the armature A, a resistor r<SP>1</SP> being connected across the armature A<SP>1</SP> so providing dynamic braking of the motors. The connections controlled by the contacts 1AS1 and 2AS1 may be utilized to provide shunts for the armatures during low-speed power operations, so affording stable conditions with varying load. In the system of Fig. 2, separate exciters E1 and E2 are provided to energize the motor field windings F and F1, the exciter field windings f and f<SP>1</SP> being connected directly across the motor armatures. Movement of the master controller MS1 to the " off " position de-energizes relay-windings 3DF and 4DF to connect the motor field windings to the exciters through contacts 3DF1 and 4DF1. In the " off " position of relay-windings 11DB and 21DB is transferred to a push-button PB which, when opened, de-energizes those windings and closes contacts 11DB1 and 21DB1, so connecting resistors r4-r5 across armature A and resistors r6-r7, across armature A<SP>1</SP>. Contacts 11DB2 and 21DB2 are engaged respectively to energize a relay-winding T and to de-energize its time-delay winding 2T. Contacts T1 are then opened to deenergize relay-windings 12DB and 22DB so closing contacts 12DB1 and 22DB1 and short-circuiting resistors r5 and r7 respectively. Response of relays 12DB and 22DB closes contacts 12DB2 and 22DB2 in the circuit of relay-windings 13DB and 23DB, and, when the braking-current through relay-windings 1SR and 2SR decreases sufficiently, contacts 1SR1 and 2SRI close and resistors r8 and r9 are shunted across the motor armatures through contacts 13DB1 and 23DB1. With the main controller in the " off position, coasting operation of the motors is afforded until actuation of the push-button PB initiates dynamic braking. During coasting the motor field windings are energized by the exciters E1 and E2. Voltage relays 1VR and 2VR are provided to effect tripping of a no-voltage relay UV if the exciters do not develop sufficient voltage during the acceleration period. Either motor may be removed from service without affecting the dynamic braking control of the otner. A restraining winding 2P of a plugging- switch is selectively connectable across one of two resistors, each of which is associated with a separate motor. Specification 513,814 is referred to.