GB320931A - Improvements in or relating to induction dynamo-electric machines - Google Patents

Abstract

320,931. Gill, J. F., and Chaviara, J. N. July 25, 1928. Alternating - current induction machines.- For power-factor improvement in induction motors or generators of the type consisting of two rotors, coupled both electrically and mechanically and giving equal or different voltages and equal currents, and two stators directly connected in series or parallel to a common supply, the ratio of stator to rotor ampere turns on load in the two machines is made respectively greater and less than unity and the k.v.a. capacity of the machine with the smaller ratio is made greater than that of the other; in addition, the two machines operate at different flux densities and stator magneto-motive forces, the machine which has the higher density and magneto-motive force having a lower k.v.a. capacity than the other one. The Specification describes, with the aid of vector diagrams, the actions in such a pair of coupled motors whereby one part is caused to act as a normal motor and the other as an under-excited machine so that the leading wattless k.v.a. in the one compensates the lagging k.v.a. in the other. Fig. 4 shows in outline a squirrel-cage machine in which the two portions a<1>, b<1> of the rotor are separate and carry a common cage. The stator element b, which has a magneto-motive force greater than that of its rotor, has a greater number of turns than the other stator a, this being effected by employing two sets of star-connected series-wound turns one of which is wound around the stator b only and the other around both stators in a 3-phase star system. The total k.v.a. rating of the machine a, a<1> is greater than that of the machine b, b<1> but per unit length of rotor it is less. In place of using a single machine divided into two parts as in Fig. 4, two separate machines may be employed with their slip-ring rotors mechanically and electrically coupled. Specifications 9534/00 and 6956/09 are referred to.