*2.3. Mechanical Unbalance Fault (UNB)*

When the mechanical load of the induction motor is not evenly disseminated, displacing the center of mass out of the motor rotating axis, there is an unbalance fault. A manufacturing defect is the principal cause of rotor unbalance; also, heating dilation has an effect on the internal misalignment or the shaft deviation that produces an unbalanced rotor. The unbalance state occurs when there is an uneven distribution of weight around the rotor center of rotation, generating an unbalance force *U*, which is given by

$$
\mathcal{U} = m \times r \tag{3}
$$

where *m* is the mass and *r* is its eccentricity, which is the separation between the rotor center of mass and its rotating axis. Unbalance force fluctuates with the rotating speed and drags the rotor off from the stator center bore to a distinct position, which is known as the heavy spot. Mutual inductances between stator and rotor loops get to be uneven because of the rotor unbalance, which results in frequency components induced in the stator current that are given by

$$f\_{unb} = f\_s \left[ 1 \pm k(1 - s) / p \right], \ k = 1, 2, 3, \dots \tag{4}$$

where *f* s is the fundamental frequency of the electric current supply, *k* is an integer number, *s* is the motor slip, and *p* is the number of pole pairs in the SCIM [21].
