Analysis of stray loss and its determination with equivalent circuit for double cage rotor induction motor

Abstract

For accurate determination of induction motor (IM) efficiency, precise knowledge of motor losses are required to be known. Stray loss constitute a part of the total loss and hence its detailed analysis and accurate determination is required. Classical IM theory and its equivalent circuit do not consider stray loss in it, resulting in inaccurate performance evaluation. In this work, analysis of the stray losses and its determination using proposed equivalent circuit is done. Finite element method (FEM) is used for core loss analysis and to obtain the stray losses for an inverter fed double cage rotor IM. Stray loss in IM due to loading, presence of harmonics frequency voltage, and slot harmonics is determined by observing core loss increase using FEM. Core material with known core loss data at different frequencies is used. FEM facilitates precise core loss calculation due to the availability of accurate magnetic field density distribution on loading, presence of harmonics frequency voltage and slot harmonics. Individual equivalent resistance each representing stray load loss and stray harmonics loss is determined. A complete equivalent circuit of double cage rotor IM considering the stray loss is then proposed, and its parameters are also determined. This work is applicable for all rotor types in IM. Different components of stray loss with varying load condition is calculated from the proposed equivalent circuit and are compared with those obtained from FEM to validate the results.