Determination of NEMA Design Induction Motor Parameters From Manufacturer Data

This paper proposes a simple method of determining the equivalent circuit parameters of National Electrical Manufacturers Association (NEMA) design A and B types of induction motors from standard manufacturer data such as rated output power, starting torque, breakdown torque, and efficiency and power factor at rated output power. A set of nonlinear equations for various quantities is first derived from the equivalent circuit with a single-cage rotor model, and then, equate to the corresponding actual values supplied by the manufacturer. These equations are then solved using a least-squares based algorithm to determine the motor parameters. The rotor parameters are considered as slip dependent to predict the starting torque of the motor and that requires refining the breakdown torque equation as well as the slip at which the breakdown torque occurs. The proposed method of determining the motor parameters is then tested on more than 300 large-size HV induction motors. The effectiveness of the proposed method is evaluated by calculating various external quantities of the motors through the estimated parameters and comparing them with the corresponding actual values supplied by the manufacturer.