Patent GB-190311304-A (GB)
Title: Improvements relating to the Control of Electric Motors.
Filed: 1903-05-18
Granted: 1903-12-03
Abstract: 11,304. Johnson-Lundell Electric Traction Co., [Lundell, R.]. May 18. Motors, controlling.-Relates to the starting and controlling of compound-wound motors which are at times driven as dynamos by the load, such as those described in Specification No. 26,668, A.D. 1902, especially such as are applied to overbalanced electric elevators or lifts, and comprises means for giving the motors a wide range of predetermined or fixed speeds which are practically independent of the armature currents, means for starting the motors and automatically accelerating the speed up to the lowest fixed speed, means for changing the armature circuits of two or more motors from series to parallel, or vice versÔ, without interrupting the current from the power circuit and without departing from the predetermined or fixed speeds while the circuits are being changed, and means for applying a brake when the electromotive force of the motor exceeds that of the power circuits owing to a failure of the power circuit from any cause. In the form shown, two motors, which are mechanically connected by gearing, are employed, each provided with two armature windings, viz., A', AA' and A<2>, AA<2>, but four motors with single-wound armatures, or two motors with single-wound armatures in combination with two different voltages in a three-wire system, might be used. Fig. 1 shows the fixed contacts f<1> to 12 of a main cylinder and 1 to 28 of a reversing-cylinder, and developments of the movable contacts of these cylinders. It also shows the armature windings, the series field windings F<1>, F<2>, shunt windings Sh<1>, Sh<2>, low resistances r<1>, r', for practically short-circuiting the series windings, high resistances b<1>, c', d' and b<2>, c', d<2> for the shunt windings, a relay, several electromagnetic switches, and a starting-resistance Sr. Fig. 12 shows the connections made at each position of the controller, which is operated electrically or manually by a suitable rope connection with the car. Commencing with the reversing-switch closed in either the up or down position, and the main switch in its 'off' position 0-0, the shunt fields Sh<1>, Sh<2> are weakly energized, and the ground connections of the switches C, D are closed. The first movement of the main switch energizes the magnet B, thereby releasing a friction brake, closes the starting-switch C, and short-circuits the resistances b<1>, c', d<1>, b<2>, c<2>, d<2>, whereby the shunt fields are strongly energized. The circuit through the motors is thus established as shown in the second diagram, and, as the switch C closes, the electromagnet D is energized and short-circuits the starting-resistance Sr, as shown in the next diagram in Fig. 2. Thereupon the electromagnets M<2>, M' operate to short-circuit the series field windings F', F<1> through the low-resistances r<2>, r<1>, as shown in the diagram for first speed, thereby causing the field strength and the speed of the motors to become practically independent of the armature currents. Further movement of the main cylinder successively makes the connections shown in the remaining diagrams in Fig. 2, whereby the speed of the motors is increased step by step. In the second position, the field strength of the second motor is reduced by the introduction of the resistances b<2>, c<2>, d' into the shunt-field circuit. In the third position, the shunt-field circuit is opened. In the fourth position, the short-circuit round the series field F<2> is opened, and a by-path is closed round the second motor, the speed becoming now about double the first speed. In the fifth position, the armature and series field of the second motor are opened, and its shunt field is closed through b<2>, c<2>, d<2>; the shunt field Sh<1> is also weakened by the introduction of the resistance b<1>. In the sixth position, the second motor is connected in parallel with the first, while the series field F<2> adjusts the field strength of the second motor ; the shunt Sh<1> is also further weakened by the introduction of the resistance c<1>. In the seventh position, the second motor becomes the controlling-one, the armature circuit of the first being opened. In the eighth position, the two armature circuits A' and AA' are put in parallel to the power circuit, with the series field F<1> in series, making the field strength of the first motor self-regulating. The speed is now about four times that at the first position. In the ninth position, the second motor is again cut out and the first again becomes the controlling-one, with a weaker field. In the tenth position, the armature circuits of the second motor are connected in parallel to the power circuit with the series field F<2> in series for causing self-adjustment of field strength. In the final position, the motors are run in parallel with weak shunt fields, the series fields F<1>, F<3> being short-circuited through the low resistances r', r<2>, so that the speed is fairly independent of the armature currents. The speed is now about eight times the first speed. A relay, Fig. 1, breaks the circuit through the brake coil B and the starting- switch coil C. Whenever the electromotive force between the terminals L+, L-becomes greater than that for which the relay has been adjusted, so that, when the motors cease to act as regenerative brakes, a friction orake is applied.