Design synthesis of double-cage induction motors

The paper presents a method for synthetising the equivalent-circuit parameters of double-cage induction motors to attain specified levels of starting, accelerating, breakdown torque and running performance. New equations are derived, avoiding certain approximations which have commonly been made hitherto, and these equations are used to relate the equivalent-circuit parameters to the motor performance. A new synthesis procedure is then developed, based on these equations and relationships. The procedure includes a number of sections which are essentially iterative, and it is consequently most conveniently embodied in a digital-computer program. Since the reduction of leakage reactances owing to magnetic saturation is an important factor in motors with arduous starting duties, a method is proposed for taking this effect into account. Using, as a starting point, an approximate representation of the shape of typical curves of leakage reactance against current, equations are derived to represent the saturation effect in a form which isconveniently incorporated in the computer program. Only two additional items of input data are required to specify the saturation effect, these being the current at which saturation commences and the ratio of saturated to unsaturated starting currents. The successful operation of the synthesis procedure is demonstrated by a number of examples, including some in which the computed design is compared with a prior manual design to the same specification.