Equivalent core length consideration of synchronous motor with radial air-ducts by using 3D electromagnetic finite element method

Abstract

This paper presents the analysis results on the equivalent core length of MW salient pole synchronous motor with the air-ducts in the radial direction. The use of radial cooling channels has an effect on the electromagnetic performance of its motor. The main effect is that the actual core length must be replaced with the effective core length from the point of view of two dimensional electromagnetic circuit. Some papers or books for the design of the rotating machine explain this phenomenon as the fringing effect and express it as the formulas. 2D electromagnetic FEM analysis is carried out based on the formula for the calculation of effective core length. 3D FEM is also carried out to confirm if the use of the calculation is appropriate or not. As a result, there is 10% deviation of the no-load voltage between 2D and 3D FEM result. It means that the calculation, which stands for the fringing effect has to be reconsidered. Hence, it is needed to analyze the cause of the error by using 3D FEM analysis for more precise calculation of the core length, which affects values such as no-load voltage, field current and load torque in 2D perspective. Open circuit characteristic test is also carried out to compare and verify 3D FEM result.