GB253127A - Improvements in and relating to the control of electric generators and interconnected motors - Google Patents

Abstract

253,127. British Thomson-Houston Co., Ltd., (Assignees of Macmillan, C.). June 3, 1925, [Convention date]. Dynamos and motors combined for transmitting power.-In a system comprising an induction motor supplied from an alternating current generator the variations of secondary circuit resistance to obtain variations of motor speed are associated with abrupt changes of excitation of the generator so that either (a) a series of definite speeds without great variation of primary circuit voltage or (b) a steady variation of motor speed may be attained. The means for varying the secondary circuit resistance are correlated with means for suddenly increasing or decreasing the excitation of the primary circuit so that, allowing for the true constants of the circuits, each alteration of secondary circuit resistance may be accompanied by a sudden variation of field excitation in the appropriate sense, followed by a gradual variation of excitation as the motor accelerates. An arm 32 controlling the field circuit resistance is geared to a sector 23 controlling current supplied to contactors 16 - - 19 controlling the rotor resistance 2 so that one turn of the arm moves the sector over the space between two adjacent brushes 25 - - 28. Movement of the arm 32 counterclockwise from the position shown suddenly reduces the field excitation and causes the sector 23 to energize contactor 17 to reduce the rotor resistance, thus producing a gradual acceleration of the motor at each variation of rotor circuit resistance. By reversing the switch 31 a reduction of rotor resistance is accompanied by a sudden increase of generator excitation followed by its slow decrease as the motor accelerates, this arrangement providing a series of definite motor speeds without great variation of voltage.