I. Introduction
Three phase squirrel cage induction motor is one of the most used machines in different types of industries such as petrochemical, mining etc., for having several advantages over the other types of machines e.g. robustness, being less expensive, easy maintenance, ranging from small (a few watts) to large (up to 10,000 hp) ratings etc. Nevertheless, industrial induction machines operate in an industrial environment and hence are prone to various faults caused by different electrical, mechanical and environmental factors. Depending on their types and severity, faults may cause a small deterioration in the motor performance developing into a catastrophic damage, which may take a few months or only a few seconds to escalate. Therefore, one of the main concerns of the researches related to induction motors are focused on detecting the faults at an incipient stage, so that the maintenance and/or replacement cost can be reduced by a significant margin. For example, the cost for replacement of a 100 hp, 3 phase AC motor is 7,500 USD (approx.), whereas replacing the same motor's bearings costs only 250 USD (approx.) [1].