In the literature we can find two approaches to make diagnosis: Model approach - a specific method for automation engineers. Depending on the mechanism adopted, we can distinguish three branches in this method: monitoring by observers, by analytical redundancy and by parametric estimation. Signal approach - this approach is based on measurable signals data, such as current, torque, stray flux, noise and vibration, temperature. The principle of this method is to look for frequencies unique to the healthy or fault operation. Faults in electrical
rotating machines can induce other phenomena such as noise and vibrations and possibly other faults like friction between the stator and the rotor or accelerated wear of insulations.