GB1379040A - Control circuits for dc electric rotating machines - Google Patents

Abstract

1379040 Controlling starting of a DC motor HITACHI Ltd 29 Dec 1971 [29 Dec 1970] 60375/71 Heading H2J A D.C.-motor starting circuit includes series connected, different valued starting resistors, shunted in a predetermined order to keep the motor armature current between preset limits, and a variable resistor including a current chopper, whose effective resistance immediately prior to the shunting of each starting resistor is set to the value of that resistor. In an embodiment, the starting of an electric train, having a D.C. motor 4 which is connected through a circuit-breaker (not shown) and pantograph 2 to an overhead power supply 1, is controlled by shunting starting resistors, 5 to 10, each of different values, by closing switches 11 to 16 by controller 21. This controller also varies the current in a current chopper 81, forming part of the variable resistance 17, that also includes a switch 20 and resistor 19, which is at least as large as the largest starting resistor. Upon starting, the resistors 5 to 10 and 19 are_in circuit and chopper 18 is not conducting. Speed is increased by increasing the conduction period of the chopper 18 until resistor 19 is at least partially short circuited and a minimum armature current (Io, Fig. 5, not shown), is detected. Then the chopper conduction period is reduced so that the variable resistance is equal to the starting resistor 5 to be shunted, the armature current rising smoothly, in a short time such that the motor speed does not increase, until the armature maximum current (Ic) is reached, then switch 11 is closed by controller 21 to shunt resistor 5, the chopper conduction being simultaneously reduced to zero. The chopper conduction is then increased to repeat the cycle for each starting resistor, until, at full speed, resistors 5 to 10 and 19 have been shunted by switches 11 to 16 and 20 respectively. Thus the armature current range is limited to a minimum (Io) and a maximum (Ic), which may be the maximum permissible armature current, allowing the minimum number of starting resistors, and overshoot when shunting the starting resistors is avoided. The switches 11 to 16 may be solenoid operated or SCR switches, and the variable resistance 17 could comprise further switchable resistors in parallel with resistor 19, Fig. 2 (not shown).