The rotor is a non-stationary part of a rotary electric motor, which rotates to produce the torque by wires and magnetic field arrangement. Before knowing how a rotor eccentricity affects motor performance, it is essential to know about rotor eccentricity. Eccentricity is the behavior of any entity. Just as we learn to calculate the eccentricity of parabola, hyperbola, etc., in a similar context, calculating the eccentricity of rotors occurs because the rotor is also a geometrical figure. The eccentricity of rotors can affect the whole operation according to the size and function of the motors.
Eccentricity errors occur during the operation of electrical machines in cases of change in rotor position. The most common error occurs if the space fills with air in the motor, i.e. if some blank space fills with air at the time of designing. There is the probability of introducing irregular stresses in the cage of the rotor during the process of its manufacture. This may cause bending of the lamination stack of the rotor.
The eccentricity that arises owing to the blank air space gives negative results like more stress on the machine during the operation, decrease in efficiency, and some mechanical problems. All these issues lead to improper functioning of a motor. There are two types of blank air spaces in motors. They give rise to static and dynamic eccentricity.
Rotor pullover is one of the most common instances of the rotor rub, which can lead to the twisting of the motor shaft, thereby causing the rotor to compress. This causes a blank air space error in the motor. This open-air space is an error, which has materialized during the motor production; this is a type of mechanical error, not an electrical error.
This error generally occurs when the distance between motor and shaft varies. In other words, the cause of the blank air space is the uneven pull between the stator and rotor during operation, which leads to the increase in above stated problems. There is equipment used to check the eccentricity of the rotor like an MCE RIC test and an EMAX test (high frequency spectral analysis test).
Eccentricity is a mathematical error that will reduce by opting for some numerical methods. It arises due to a rotor’s shape that is somewhat spherical in nature. The shape cannot change, but some variations in design and functionality can solve the problem. These resolutions can deliver efficient functionality of the motor and even increase its productivity.