GB241391A - Improvements in direct current dynamo electric machine groups - Google Patents

Abstract

241,391. English Electric Co., Ltd., and Calverley, J. E. Oct. 22, 1924. Exciting motor - generators. - In a continuous - current motorgenerator set in which the motor supply volts vary considerably, as in the case of a lighting set en an electrically-driven train, a substantially constant voltage is obtained at the generator terminals by means of an exciting winding, either on the motor or generator, carrying a current which depends on the difference in voltage between the generator and an exciter. Fig. 1 shows the application to a double commutator motor 9 driving a generator 1 and exciter 2, the motor being relatively unsaturated and the generator saturated at normal line volts and speed. The exciter is preferably less saturated than the generator and at low speeds there is a material difference between the voltages of these two machines which falls off as the speed rises. The opposing machines 1, 2 have a common connection on one pole and are connected on the other pole through compounding coils 3, 4 and an optional regulating resistance 5. At low speeds, the generator volts predominate and the compounding assists both of the main exciting coils 6, 7, the coil 7 being connected across the line in series with the motor shunt coil 8 and so giving the exciter and excitation proportional to the volts applied to the motor. Increase in line volts considerably increases the volts of the unsaturated exciter in comparison with these of the generator and so cuts down the current in the compounding coils 3, 4 and reduces the generator volts. If the volts supplied to the motor are too high to render shunt excitation desirable, it may be excited from the generator terminals, the exciter coil 7 being either in series or parallel with the motor field coils. The regulation to constant volts may also be effected by controlling the motor speed, as in Fig. 3, in which case the generator has a plain shunt winding 6 in parallel with the main motor coil 8, and the compounding coil 13, which carries a current due to the difference between the generator and exciter volts, is transferred to the motor in opposition to the coil 8. Fall of speed of the set, caused by reduced line volts, is corrected by an increase in the compounding current and consequent weakening of the motor field. The motor in any of the cases described may be compounded.