GB413038A - Improved means of control for regenerative electric motors - Google Patents

Abstract

413,038. Control of D.C. motors. GUY MOTORS, Ltd., Fallings Park, Wolverhampton, and STEVENS, W. A., Castlemaine, London Road. Maidstone. Kent. Jan. 31, 1933, No. 2930. [Class 38 (iii).] Regenerative braking.-In a control system for a compoundwound traction motor b with regenerative braking and means for shunting the series field winding c during motoring and regeneration, a magnetic system controlled by the armature current is provided for automatically increasing the resistance of the said shunt whenever the armature current exceeds a predetermined maximum. In the arrangement shown, movement of the driving pedal to its first position closes contactors e, el, short-circuits a resistance m in series with the shunt field winding k, and connects the motor to the line through the main series resistance d. Further movement of the driving pedal closes contactors f and successively short-circuits sections of the resistance d, after which a contactor h closes to insert a shunt i across the series field winding c. Further forward movement of the pedal successively short-circuits sections of the shunt field resistance l until the motor attains a high speed. On allowing the pedal to return towards the middle position, with resulting strengthening of the shunt field, the machine acts as a generator and returns current to the line through the series field winding c. When this happens, a polarized relay controlled by windings a<1>, j closes a contactor n, which inserts a variable shunt across the winding c, to reduce the demagnetizing effect of the latter. This shunt comprises a resistance o and a series of parallel resistances s<1>-s<4> adapted to be cut in or out by movable contact arms q<5>-q<8> carrying armatures q<1>-q<4> mounted above an elongated core p magnetized by a winding p<1> in series with the armature b. The contact arms are normally held in engagement with fixed contacts r<1>-r<4> by adjustable springs r. As long as the current through the winding p<1> is below the predetermined value, the series winding c is practically short-circuited through s<1>, but as soon as the current exceeds this value the circuit is opened at s', with the result that the series winding will set up a field opposing that of the shunt winding k and tending to reduce the current. If the current is still excessive, one or more of the shunt resistances s<2>-s<4> is cut out by attraction of the corresponding armature q<2>-q<4> to increase still further the demagnetizing effect of the series winding. In a modification, Fig. 4 (not shown), the contacts r<2>-r<4> following the contact connected to the short-circuiting piece s<1> are of carbon, and the resistance at the contacts increases when the pressure is reduced by the action of the armature current.