GB509884A - Improvements relating to d.c. dynamo electric machines controlling the supply to electric motors and other variable loads - Google Patents

Abstract

509,884. Exciting dynamos. ENGLISH ELECTRIC CO., Ltd., BINNEY, E. A., CORNER, H. S. POUND-, and SEDGFIELD, H. B. Jan. 10, 1938, Nos. 718/38 and 623/39. [Class 35] [Also in Group XXXVII] A motor-generator set comprises a machine excited by a shunt field winding in series with which winding is an exciter having three fields, one energised in accordance with the armature current of the machine, another separately excited, and a third connected across the exciter armature, the exciter being mechanically coupled with the machine, and the set operating to maintain a predetermined current in the load circuit. The machine 6 is driven by a motor 1 and controls series motors 7, 7b by first bucking and then boosting the voltage of the suppiy. The motor 1 is first run up to speed and the motor circuit made by closing a switch 11. The field 6a of the machine 6 is thus excited and builds up a voltage equal and opposite to the supply voltage. To accelerate the motors a switch 8 is closed, and subsequently the field 5b of the exciter 5 energised by closing a switch 13. The voltage of the exciter reduces the excitation of the machine 6, and the motors accelerate, the motor current flowing through the exciter field 5a and setting up a field opposing the field 5b. The motor current is maintained constant by the balancing action of the windings 5a, 5b, the value being determined by a regulator 5c for the field 5b. As the motors accelerate the field 5a is reduced and the exciter voltage effects a decrease of the excitation of the machine 6 which decreases the voltage applied from its armature to its field 6a and further reduces the excitation. The action continues and the motors 7, 7b accelerate until the voltage of the machine'6 6 is zero. The action is allowed to continue while the machine 6 builds up a voltage equal to the line voltage. The exciter shunt field 5d may assist or oppose the field 5a in maintaining the motor current, and it may assist during the bucking and boosting control of the motors, while opposing during excitation of the motor fields from the machine 6 after the motors at full voltage have been transferred to the external source. A series winding may be added to the exciter 5. A resistance 10 in the circuit of the field 6a may be controlled by a relay to compensate for the difference in the action of the set during bucking and boosting operations. The driving motor 1 may be arranged so that its armature reaction causes changes in speed which assist in maintaining the motor current during boosting control. The series winding of the motor 1 may be in circuit for the boosting control only, and this motor may have a field energised from the armature of the machine 6 to strengthen the motor field during bucking control and weaken it during boosting. Alternatively this additional field may be connected for boosting only. Specifications 485,312, 509,041, 509,138, 509,239; [both in Group XXXVII], and 509,884 are referred to.