Patent GB-191010370-A (GB)
Title: Improvements in Systems for Controlling Electric Motors.
IPC: H02P7/34
Filed: 1910-04-27
Granted: 1911-01-12
Abstract: 10,370. Marks, E. C. R., [Felten & Guilleaume-Lahmeyerwerke Akt.-Ges.]. April 27. Dynamos and motors combined for transmitting power.-In a power transmission system, the shunt or separately excited field of the dynamo is controlled by an electromotive force which is proportional to but independent of the main current, in order that the speed of the motor shall be independent of the remanence of the dynamo and the loss of voltage in the main circuit, and exclusively dependent on the regulation of the shunt or separately excited field of the generator. In the arrangement shown in Fig. 2, the generator a is provided with a series field c and a separately excited field f, the current through which is regulated by means of a resistance r. To the separately-excited driving motor m is coupled a generator d producing an electromotive force proportional to the speed of the motor m, which electromotive force may act in conjunction with the current in the field winding f upon a differential device to regulate automatically the current in the field winding f. A resistance s is placed in the circuit of the field winding f, and the generator d connected across this resistance. If the speed of the motor m causes the generator d to produce a voltage equal to the fall of voltage across the resistance s, no current will flow through the generator d. If the remanence of the generator acts in a positive sense and the speed of the motor m is consequently above the normal, the electromotive force of the generator d is increased, and the current through the winding f is reduced to decrease the speed of the motor m. If, however, the remanence of the generator a acts in a negative sense and the motor m is at rest, the generator d short-circuits the resistance s, thereby increasing the current through the winding f to cause the motor to start. Since the percentage differences due to remanence and ohmic losses decrease as the excitation of the generator a increases, the resistance s is decreased as the excitation of the generator a increases, and vice-versa. In a modification of this arrangement, the generator d may be replaced by an extra winding on the motor, or by the back electromotive force of the motor m; while in a further modification, shown in Fig. 3, the generator d is in series with the resistance across the terminals of the field winding f. Under normal load conditions, the voltage of the generator d equals the voltage across the field winding f; while under abnormal load conditions, the voltage of the generator d falls, thereby forming a shunt to the field f, which reacts further to lower the speed of the motor m. The maximum current in the motor circuit, when the motor is at rest, is determined by means of the resistance r. The generator d is designed to produce a comparatively high voltage at low speeds, so that at full speed the voltage of the machine must be reduced. This is effected by weakening the field of the generator as its speed increases, by placing it across the varying resistance r connected up as shown in Fig. 2. In the arrangement shown in Fig. 5, the armature w<4> of the motor m is placed in one arm of a wheatstone-bridge arrangement, the points o, p of which are connected through the resistance s in series with the field winding f. Under normal conditions, the voltage across the points o, p is equal to the fall of voltage across the resistance s. Under abnormal conditions, however, the voltage across the points o, p is caused to increase or decrease the strength of current through the field winding f. At high speeds of the motor m, the resistances w<2>, w' in the arms of the bridge arrangement may be thrown out of operation to avoid loss of energy.