Mechanical vibration of three-phase induction motors fed by nonsinusoidal currents

The problem of failures in large electrical machines is a great concern due to its decisive influence over industrial productivity. On the other hand, recent developments in the power electronics field have lead to an extensive use of static drives to control the current, torque and speed of AC motors. In these cases, new mechanical stresses invariably appear which have detrimental effects on the motor performance. This work describes from practical and theoretical points of view, a method method to establish the relationships between current measured induction motor vibrations. The theoretical model includes the effect of airgap eccentricity, iron saturation, and stator and rotor slotting on the harmonic vibration analysis. The method is useful to detect anomalous behaviour associated to singular incipient motor failures. To analyze these problems, the measured three-phase current waveform is used for calculating the forces causing the main dynamic disturbances. Airgap eccentricity and saturation levels as both included in a computer based diagnostic analysis system. The vibration spectrum is obtained and related with the harmonic currents; also, a classification of electromagnetic forces using the stress space distribution is carried out. The study reports that the harmonic current from static inverters can produce high stator frame vibration and the degree of severity of this phenomena is related with motor airgap eccentricity and the saturation level of the induction motor