Patent GB-190625203-A (GB)
Title: Improvements in and relating to Electric Motor Control Systems
Filed: 1906-11-08
Granted: 1907-11-08
Abstract: 25,203. British Thomson-Houston Co., and sporborg, H. N. Nov. 8. Switches.-Relates to the control of alternating- current electric motors by means of separatelyactuated switches which vary the voltage progressively, a ' preventive' resistance being switched into and out of the motor circuit during each complete change of voltage, for the purpose of preventing the formation of a short-circuit across the points of different voltage, and also for reducing the abruptness of the effect. According to the present invention, the separately-actuated voltage-controlling 'contactors' are arranged in groups, the contactors in each group being connected to a common bus-bar. A motor-circuit controlling-switch is provided for each group, and is adapted to connect the bus-bar in the motor circuit. The voltage contactors are so interlocked with the motor circuit switches that the latter, when closed, are rendered independent of the former. The separately-actuated contactors &c. are operated electrically by a master controller, or by other means, e.g. electro-pneumatic. The required voltages may be obtained by a variableratio transformer or by variable resistances. The Figure shows an arrangement in which two motors A, A' of the compensated-series type' are supplied with current from a variable-ratio transformer or compensator d. Alternate taps d<1>, d<3>, d<5> are connected to a common bus-bar a through contactors 1, 2, 3, respectively ; the other set of alternate taps d<2>, d<4>, d<6> is connected to another busbar b through contactors 6, 7, 8, respectively; the bus-bars have connexions through contactors 4, 5 with the line 20 leading to the motors, and the preventive resistance c is permanently connected between the bus-bars. The Figure shows the arrangement before current is turned-on. When the master controller C is moved to its first position, the actuating-coils of the contactors 1, 4 are excited and the contactors are closed, drawing current from the first transformer tap d' through the bus-bar a. The current traverses the motor armatures in series, and then flows, if the reversing-switch R is set for forward running, through contactors 9, 11 and the field windings F, F<1> in series, the actuating-coils 9, 11 being excited simultaneously with the contactors 1, 4. The motors may have additional field windings F<2>, F<3>. When the master controller is moved to its second position, the circuits are actuated as follows: the contactor 8 leading to the second transformer tap d<2> is closed first, the resistance c preventing the formation of a short-circuit; then the contactor 1 is opened, leaving the resistance c momentarily in circuit with the motors ; and, finally, the contactor 5 is closed and the contactor 4 is opened, leaving the motor in series directly with the second tap d<2>. A similar set of operations takes place at the third and each succeeding step of the master controller. To ensure that the contactor 5 does not close while any of the voltage-controlling contactors 1, 2, 3 of the other bus-bar remain closed, these are provided with auxiliary interlocking switches g<1>, g<2>, g<3>, which open when the corresponding contactors are closed and break the ground circuit from the actuating-coil 5. An interlock of the same nature is arranged between the contactors 4 and 6, 7, 8. Auxiliary switches g<4>, g<5> provide ground circuits for the contactors 4, 5 when these are once closed, independent of the other auxiliary switches. The contactors are of the kind described in Specifications No. 20,274, A.D. 1898, and No. 18,330, A.D. 1901.