GB337906A - Improvements in electric motors - Google Patents

Abstract

337,906. General Electric Co., Ltd., and Saunders, N. F. T. Sept. 20, 1929. A.C. induction machines; armatures, cooling and ventilating.-In a squirrel-cage induction motor, the primary of which is adapted to give more than one pole number, the rotor bars are divided into sets, each of which has separate end rings, and the rings of different sets are connected by resistances through which current flows only when operating on the higher pole numbers. For the low pole numbers, the currents in the various sets are independent. The number of sets is equal to the ratio of a larger to a smaller number of poles, and the number of resistances between adjacent rings is equal to the lower pole number. In the form shown, the thirty-two bars of the rotor of a 4 or 8-pole motor are divided into two sets, and each set is divided into groups. One set comprises groups 1, 3, 5 and 7 connected between the end rings 9 and 10, and the other set is composed of groups 2, 4, 6 and 8 between rings 11 and 12. During four-pole operation, current flows in the direction of the single arrows, and as the resistances 13-20 are connected across substantially equipotential points, they do not increase the rotor resistance, whereas they do increase it during eight-pole operation since the currents then flow in the direction indicated by double arrows. The invention is applicable to machines arranged for more than two pole numbers, additional end rings and sets of resistances then being required. Preferably the resistances are in the form of arms' extending radially from a ring or hub concentric with the rotor shaft, and' may be so shaped and inclined as to act as a fan.