A Hybrid Methodology for Analyzing the Performance of Induction Motors with Efficiency Improvement by Specific Commercial Measures

Abstract

This paper presents a hybrid methodology to analyze the commercial measures of changing stator windings and adjusting air gap length to upgrade efficiency of typical three-phase direct-on-line induction motors with die-cast copper rotor (DCR). The calculation is carried out through combining the time-stepping and time-harmonic finite element analysis (FEA) and the circuit equivalent circuit model. Typical full-load performance of stator windings with different air gap lengths are computed by MATLAB invoking the 2D transient and eddy current field analysis in ANSYS/MAXWELL. Then, MATLAB scripts about post-processing of the FEA results are used to obtain the full-load running performance including the loss distribution and circulating current. The MATLAB scripts of circuit model built based on the FEA results is used to compare the overload and starting performance. After that, four stators with the four windings and three DCRs with different air gap of an 11 kW motor are fabricated and tested to validate the calculations. By comparing results from both calculations and measurements, it is shown that the factors of stator windings and air gap length can effectively improve the efficiency of the 11 kW DCR induction motor without the addition of extra materials. The motor with the 11/12 pitch Y-∆ series winding and 0.6 mm air gap has the best performance, in terms of efficiency, overloading capability and starting performance. Its efficiency can increase from 90% to the highest 92.35% by sole adjustment of stator winding and air gap length.Many technical measures have been investigated for improving the efficiency of induction motors. The higher efficiency can usually be achieved by increasing the active materials, such as increasing the stack length [5,6], in induction motors. Another measure of upgrading materials such as premium electrical grade lamination steel is used for decreasing core losses and Ohmic losses [6][7][8].The efficiency can also be improved by enhancing the performance of cooling and bearing systems to reduce the mechanical losses [7] and improving cooling performance to make Ohmic losses less significant [9]. These methods either rise the raw material cost or increase manufacturing complexity. Although geometry optimization techniques [10][11][12][13][14][15][16] can be used to increase the efficiency of induction motors without increasing the active materials, this technique ends up producing a different design from the original one. Consequently, a new stator and rotor punching mold is required and additional cost results. It can be seen that in practice these measures can only be used to design a new motor, therefore many manufacturers have paid more attention to ways of increasing the efficiency of their induction motors with the least cost. That means the techniques should change construction or parameters of the existing motors as little as possible. Die-cast copper rotor (DCR) technology that involves the development of heated nickel-base alloy dies presents a potential route to design hi...

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