Induction Machine Efficiency Evaluation Using the Finite Element Analysis Software and a New Mechanical Loss Formula

The ability to consider saturation of core magnetic materials, skewed rotor bars, stator winding distribution and leakage fluxes has led to the widespread use of finite element method (FEM) in analyzing the performance of different electric machines. However, due to the FEM's inability to determine mechanical losses, stray load loss and core loss of the machine, FEM results are not reliable for efficiency estimation. This paper provides some useful points to evaluate efficiency of electric machine at different loads. For this purpose, losses of the machine are directly calculated by utilizing FEM results and empirical formulas. Furthermore, by investigating more than 100 IMs with 4 poles at different rated power, a new formula based on the rated power of the machine is proposed to estimate the mechanical losses. The new formula is used to improve the accuracy of estimated efficiencies. Experimental results are utilized to validate the proposed formula.