Operation of an induction motor supplied by voltage containing subharmonics

Abstract

The paper discusses the effects of the presence of subharmonics (i.e. frequencies lower than the basic 50 Hz) in the voltage supplying the induction machine. Subharmonics in a three-phase grid are the result of the oscillations of peak values of the voltages. In induction machines, this results in the subharmonic and interharmonic currents, the generation of alternating moments, the increase in the rms value of the current of the fundamental harmonic and the oscillations of the rotor speed. In the paper is derived expression on the thermally acceptable load of the motor (by torque and power), in the case of supplying it by three-phase voltage containing a positive sequence of subharmonics. It presented the obstacles to derive the analogical expression for power supply containing a negative sequence of subharmonics.