Mixed eccentricity in three phase induction machines: analysis, simulation and experiments

Fault diagnosis of electrical machines is gaining particular importance in view of machine downtime and revenue losses to the industry. Often, these machines run critical loads and their sudden breakdown can be catastrophic. Thus, the drive system of the motor should also have diagnostic features to predict machine faults at their very inception. Consequently, it becomes very important to have machine models and control techniques that can distinguish between the healthy and faulty condition of machines. Quite a few of these faults are eccentricity related. In practice, static as well as dynamic eccentricity, happen to exist simultaneously. With this point in mind, an analytical approach to evaluate performance of a three-phase induction motor under mixed eccentric condition has been presented in this paper. A clear relationship between the high and low frequency components reported earlier in literature has been established. The analysis is validated by the line current spectrum of the eccentric machine obtained through simulation. The effects of the number of rotor slots, machine pole numbers and load conditions; which can change the current spectrum considerably; can also be studied. The fault condition has been simulated using modified winding function approach (MWFA). Finite element results to substantiate the inductance values used in the simulation are presented. Experimental results to substantiate simulations have been included.