GB611172A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

611,172. Control of D.C. motors. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. April 24, 1946, No. 12350. Convention date, Sept. 19, 1944. [Class 38 (iii)] Dynamic braking is automatically applied to an electrically-propelled vehicle on failure of the supply by a normally closed switch which is opened by the application of supply voltage before actuation of one motor controller from its " off " position. Supply of current to the motors is dependent upon the opening of this switch and after emergency braking current cannot be restored to the motors until the controller has been returned to its " off " position. The operation of one overload relay does not cause dynamic braking. The invention is described as applied to an electric trolley vehicle. In the Figure, when switch CS is closed, the supply voltage energizes a magnet coil to open the normally-closed contacts S in the dynamic braking circuit and to close contacts S1. Movement of controller C will now energize-through contacts S1-a coil to close contacts M and auxiliary contacts M1; the former connect motors 10 and 11 to the supply, the latter parallel contacts closed only on the first step of the controller. Failure of the supply causes contacts S1-and hence contacts M-to open; contacts S close to connect the motors 10 and 11 in two closed circuits through braking resistance BR, each motor energizing the series field of the other. Contacts M cannot be reclosed until, on restoration of the supply, contacts S1 reclose and, because contacts M1 are open, until the controller is returned to its first position. The overload magnet causes contacts M to open, without affecting contacts S, and also closes the circuit of a coil for maintaining itself until the controller is brought to the " off " position.