Background. The calculation of equivalent circuit parameters of induction motors according to nameplate data is widely used in engineering practice and implemented in several software packages (such as MATLAB, ETAP, Power Factory, and others). However, such tools do not always provide reliable reproduction of starting characteristics or accurate control of deviations from nameplate values. In some cases, physically inconsistent results are observed, such as the appearance of two extrema on the electromagnetic torque curve. In domestic practice, algorithms have been developed that are suitable for adaptation and integration into modern calculation tools, as well as a software prototype for simulating electromechanical transients.
Materials and methods. The study is based on equivalent circuit models of induction motors. Various mathematical approximation methods have been applied to describe the dependence of circuit parameters on slip. The materials include nameplate and experimental data of 45 induction motors of different power ratings, rotational speeds, and applications.
Results. Several alternative approaches to approximating the dependence of the equivalent circuit parameters of induction motors on slip have been examined. Particular attention has been devoted to the selection of mathematical formulations capable of ensuring improved accuracy in reproducing both starting and rated characteristics. To assess the effectiveness of the proposed methodology, a series of computations has been carried out on a dataset of 45 motors with varying rated power, rotational speeds, and industrial applications. The results of the study have revealed certain instabilities and specific features of existing algorithms implemented in widely used software packages, including cases that resulted in an unreliable representation of the electromechanical characteristic.
Conclusions. The conducted study has shown that the use of alternative approaches to approximating the equivalent circuit parameters makes it possible to significantly reduce the error when calculating the starting and operating characteristics of induction motors compared with conventional methods. The proposed approach has demonstrated more stable and accurate reproduction of nameplate parameters across a wide range of motor types, thereby covering a broad spectrum of typical operating conditions and improving the reliability of the obtained results. The modification of the rotor parameter approximation algorithm with respect to slip substantially enhances the accuracy of equivalent circuit calculations, particularly in the field of starting characteristics. The proposed expressions provide a more consistent functional form without complicating computations. The developed approach is intended for and recommended to be incorporated into domestic engineering software tools aimed at simulating electromechanical transients in power systems.