SQUIRREL-CAGE MOTOR WITH ADDITIONAL RING IN ROTOR

It is explained why certain parasitic synchronous torques generated in a squirrel-cage motor do not arise in the same motor having an additional ring in the midst of a rotor and having the both halves of a rotor turned by the certain angle γ. In other words, it is shown that an additional ring in a rotor can be employed as one of very effective means for suppressing parasitic synchronous torques in squirrel-cage motors. The expressions enabling us to calculate synchronous torques and to analyse the influence of an additional ring on their amplitudes are presented. The above allows us to determine the rule of the choice of the angle γ which enables us to suppress the synchronous torque at the chosen synchronous speed. As regards the motors in which synchronous torques arise at some different synchronous speeds the various possible cases are considered and the possibility of suppression of synchronous torques at two or more synchronous torques is discussed. As an example, a squirrel-cage motor in which large synchronous torque was suppressed with the help of an additional ring is analysed. Calculations on amplitudes of all synchronous torques are compared with results of measurements.