The Electromagnetic Torque Ripple of Three-Phase Induction Electric Machine, Operating as a Part of the Auxiliary Electric Drive Onboard of AC Electric Locomotive - a Factor Contributing to the Failure of Bearings

The paper deals with the results of computer simulation of electromagnetic torque of auxiliary induction motors and phase splitters type NVA-55 (4-pole, 55 kW) onboard of AC electric locomotive “Ermak”, which made in Russia. Because of the unbalanced system of electrical voltages (sinusoidal taken as a first approximation), except a constant electromagnetic torque component comprises in all cases the significant harmonic component of 100 Hz frequency, and in cases of squirrel cage broken bars presence - in the time harmonics spectrum frequencies from 10 Hz to 110 Hz. If we take into account non-sinusoidal form of feeding voltages signals then we shall have frequency range from 10 Hz to 700 Hz. As the NVA-55 motor bearing failures are significant, it is assumed that a contributing factor is the cyclic alternating load on the electromagnetic torque ripple causing metal fatigue failure. Proposed to use the AC variable frequency drive based on autonomous voltage inverter with pulse-width modulation control for feeding an auxiliary induction electric machines. This ensures symmetry and three-phase voltage stabilization that provides a constant sign for the electromagnetic torque of the motor with low ripple, shifted to higher frequency range.