Induction motors used as synchronous machines

The object of the paper is to determine the overload capacity of an induction motor when operated synchronously, and the pulling-in capacity at synchronism. Incidentally, in view of suggestions made in this connection in periodicals, experimental data have been obtained for (1) two methods of using a star-connected rotor for excitation, and (2) the resulting heating of rotor windings under the two methods of excitation. Further readings have been taken so as to enable curves of efficiency, power factor and stator current to be drawn. The conclusions are that the advantages of synchronous operation of induction motors are most pronounced when the method is utilized at times of light load and up to about 70 per cent of full load. At heavier loads there is a logs of efficiency and only a slight improvement in power factor. Owing to the necessity of adjusting the excitation to the load, synchronous operation is unsuitable in the case of fluctuating loads.