Combined Field and Circuit Theories in Squirrel-Cage Induction Motors Based on Micro-T Circuit Model

This paper presents an equivalent circuit derived directly from Maxwell's equations in a manner to show the amalgamation of field models and the circuit theory. A micro-T equivalent circuit is obtained from the solution of Maxwell's equations for a cylindrical representation of a squirrel cage induction motor. First, a general form of the field solution is obtained using transfer matrices. A variable transformation is then applied, which makes it possible to derive a circuit for each annular region in the motor. By joining the equivalent circuits in cascade, a complete equivalent circuit for the motor is obtained. The voltages and currents in the equivalent circuit relate directly to the field quantities within the actual motor. Accuracy of the method is verified with comparisons against finite elements and a commercial motor design program.