In this work, the optimum design of three-phase squirrel-cage induction motor has been carried out on the basis of maximization of efficiency with permissible active material cost of the motor. The objective is formed to minimize the annual cost, which is taken as the sum of the annual operating cost and a part of the initial cost accounting for annual interest and depreciation.

The problem of design of the induction motor is solved using a nonlinear programming approach. The objective function of the nonlinear design optimization problem is deduced in terms of thirteen independent motor design variables. These variables are also used to compute eleven motor performance indices, which act as design constraints. Three objective functions are considered to facilitate selection of the motor for specific applications.

Two methods, namely the SUMT (Sequential Unconstrained Minimization Technique) in conjunction with a modified Hooke and Jeeves algorithm and the Random Search algorithm are employed for a cross check and comparison. Modification to the original Hooke and Jeeves algorithm is made to improve its performance in optimizing the design of the motor. The random search method is further improved to handle integer and discrete variables. Design optimization is illustrated for a 3.73 kW three-phase squirrel cage induction motor and the results are presented and discussed in detail.

Mr. Bibhu Priya Sahu is presently working as Manager (HR-EDC) in Talcher Super Thermal Power Station of NTPC. His communication address is -Talcher Super Thermal Power Station, NTPC / Kaniha,
P.O. Deepshikha - 759147,
Distt. Angul (Orissa).