Patent GB-190721363-A (GB)
Title: Improvements in or in connection with the Control of Electric Motors.
Inventor: RAWORTH JOHN SMITH
Filed: 1907-09-26
Granted: 1908-07-09
Abstract: 21,363. Raworth, J. S., and Raworth, A. B. Sept. 26. Switches; motor control systems.-Relates to the control of series-wound electric motors for traction or haulage purposes, and more particularly to those systems of control in which the speed of the motor is reduced or restricted by placing a source of electromotive force across the series field windings, and consists in effecting this automatically by a switch controlled by the ordinary controller. This switch connects the electromotive force across the series field windings whenever the controller is moved from one running position to another towards the 'off' position, and disconnects it when the controller moves in the contrary sense. Fig. 1 shows a controller barrel developed and the connexions of the motors and sources of electromotive force, and Figs. 13 and 14 show a sectional side view and end view respectively of the additional switch mounted at one end of the controller barrel spindle 10. Fig. 1 shows the source of power 1, 2 for propelling the motors, the armatures 3, 4, the field windings 5, 6, and the additional source 7 of electromotive force for control purposes. In starting the motors, the controller is moved successively to 'running' positions I to IV, the contacts 20 of the additional switch being out of action. Whenever the controller is moved backwards towards the 'off' position, the contact 20 is automatically brought into action, and connects the battery 7 across the field windings in such a manner that the current passes through them in the same direction as the current from the propelling source 1, 2. The contact 20 is mounted on an arm 23 pivoted at 24 to a sleeve 26 loosely carried by another sleeve 18 secured to, but insulated from, the spindle 10. The arm 23 has a pin 27 secured to it, which is adapted to engage in a slot 28 in a disk 17 formed integral with or secured to the sleeve 18. When the controller is moved from the 'off' position in the direction of the arrow, the action of the slot on the pin causes the arm 23 to move inwards, thus putting the contact 20 out of action. A movement of the controller towards the 'off' position, whatever position it is in at the instant of reversal, causes the arm 23 to move outwards, the contact 20 then being in the position to engage the contactfinger 21. When the controller is in the position V, the main battery 1, 2 and the battery 7 are connected in series for charging. A modified arrangement is also described in which the battery 7 is connected in series with the battery 1, 2 and the motors during ordinary running, but is disconnected and placed across the field windings when it is desired to reduce the speed. With this arrangement, it may happen that the battery 7 becomes discharged sooner than the battery sections 1, 2, which would cause trouble. This is overcome by connecting one end of a resistance, when the controller is in positions I, II, III, between the battery sections 1, 2 and the battery 7, and the other end between the armatures 3, 4 and field windings 5, 6.