Mathematical analysis of unbalanced magnetic pull and detection of mixed air gap eccentricity in induction motor by vibration analysis using MEMS accelerometer

Air gap eccentricity fault existing in the induction motor may be of the form static or dynamic or together known as mixed eccentricity. Due to this, an unbalanced magnetic pull (UMP) will be setup between stator and rotor. This can cause bearing damage, rubbing of rotor with stator and may develop unwanted vibration and noise, which may results in premature failure of the motor. In this context, this paper presents the mathematical analysis of unbalanced magnetic pull due to air gap eccentricity in induction motor. Experimental investigations have been carried out to detect mixed airgap eccentricity fault by vibration signature analysis using Micro-Electro-Mechanical Systems (MEMS) accelerometer under different operating conditions. The spectral analysis of motor vibration has been carried out using radix-2 decimation in time Fast Fourier Transform algorithm (DIT-FFT). The presence of side band harmonic frequencies around fundamental component in the motor vibration signal spectrum indicates mixed eccentricity fault. The experimental results demonstrate that it is possible to identify the mixed airgap eccentricity fault by vibration signature analysis using MEMS accelerometer. A simple method has been proposed to find the fault severity in the motor under variable load conditions due to mixed air gap eccentricity.