Investigation of the power losses in induction machines with rotor eccentricity

Abstract

Due to manufacturing tolerances and bearing ageing, rotor eccentricity is inevitable in electrical machines. The existence of rotor eccentricity in electrical machines will cause unbalanced magnetic pull (UMP), which would increase bearing friction losses. In addition, the additional magnetic flux harmonics caused by rotor eccentricity may incur additional copper and iron losses. Here, induction machines are analysed as they are more sensitive to rotor misalignment due to smaller air gap compared to other types of machines. The magnetic flux distribution and UMP for both squirrel cage and wound rotor induction machines are discussed, as they have a dissimilar rotor configuration. The existence of rotor eccentricity would increase rotor copper loss in squirrel cage induction machines and would increase iron losses in wound rotor induction machines, where the additional power losses are a function of the degree of eccentricity. Analytical models are used to estimate the additional power losses, and they were validated using finite element analysis. Finally, we investigated the impact of power losses when implementing the slip control method which is proposed in our previous literature, in order to reduce UMP.