GB1474414A - Electric circuit for braking an asynchronous electric motor - Google Patents

Abstract

1474414 Control of A.C. motors ELITEX ZAVODY TEXTILNIHO STROJIRENSTVI GENERALNI REDITELSTVI 7 May 1974 [15 May 1973] 19955/74 Heading H2J An asynchronous motor 1 is braked by disconnecting it from its three phase supply (at terminals 11, 12, 13) and connecting it (at terminals 8, 9, 10) to a braking circuit composed of star-connected capacitor-diode pairs 2, 5; 3, 6; 4, 7, the consequent asynchronous generator operation producing a constant braking torque down to approximately one fifth of synchronous speed, below which the braking torque decreases rapidly. If a lower overall braking torque is desired, the members 4, 7 may be omitted or short-circuited. At least one of thecapacitor-diode pairs may be shunted by a resistor, Fig. 2 (not shown) to maintain the high braking torque down to a speed lower than one fifth synchronous value. This resistor also ensures discharge of the capacitors 2, 3, 4 after the end of asynchronous generator operation. In Fig. 3 two such resistors 14, 15 are used and also D.C. braking is produced after the completion of asynchronous generator operation, by means of a circuit comprising diodes 16, 17, 18, resistor 19, capacitor 20 and a switch 21. During generator operation the capacitor 20 is charged, after which the switch 21 is closed (in accordance with a function of time and/or the voltage across capacitor 20) to discharge the capacitor 20 through the motor windings and resistors 14, 15. Capacitor 20 may be replaced by a D.C. voltage source. Resistor 19 may be replaced by an adjustable resistor (22), Fig. 4 (not shown) to vary the discharge time of capacitor 20 relative to its fixed charging time.