Objectives
The objective of this experiment is to detect fault in an induction motor by using motor current signature analysis (MCSA)
Introduction
The induction motor is the most commonly used type of ac motor. Its simple, rugged construction, costs relatively little to manufacture. Large motors and permanently mounted motors that drive loads at fairly constant speed are often induction motors. Examples are found in washing machines, refrigerator compressors, bench grinders, and table saws. The induction motor has a rotor that is not connected to an external source of voltage. The induction motor derives its name from the fact that ac voltages are induced in the rotor circuit by the rotating magnetic field of the stator. In many ways, induction in this motor is similar to the induction between the primary and secondary windings of a transformer.
The most important mechanical failures are rotor broken bars, bearings damage, irregular gaps due to static or dynamic eccentricities, unbalances etc. A large number of techniques for monitoring and diagnosis of an AC motors are based on the analysis of the frequency spectrum, resulting from the FFT.
Fault detection is performed in 4 different types of motors:
1) Normal AC motor
2) AC motor with built-in broken rotor
3) AC motor with built-in bowed rotor
4) AC motor with rotor misallignment
Method of fault detection is based on the following assumptions:
i.The speed of the machine is constant and known.
ii.The stator fundamental frequency is constant
iii. The load is constant.
iv. The machine is sufficiently loaded in order to separate the sidebands frequency from the fundamental frequency.
