STARTING OF INDUCTION MOTORS AT FREQUENCIES OTHER THAN NORMAL

Abstract

The conflicting requireriaents of starting and running of induction motors efficiently are discussed. The effect of higher frequency voltages on the starting of induction motors designed for operation at normal commercial frequency is analysed theoretically and test results on a commercial motor are given. The problem is dealt with both for the case of a single higher frequency voltage wave and for voltages of different frequencies applied simultaneously. The equivalent cage resistance and reactance values for a double cage motor as adopted in standard design procedures are considered and a simple expression is developed where by a double cage motor can be represented by an equivalent circuit of a single-cage motor with suitable expressions for the rotor resistance and reactance. Test results on a commercial I 1 H.P. double cage induction motor are given to indicate the similarity of results obtained theoretically and by experiment.