NEW DIFFERENTIAL EQUATIONS FOR DOUBLE-CAGE INDUCTION MOTOR

Abstract

The double-cage induction motor became known soon after invention of single-cage motor and since then it had been designed and used in particular applications where frequent starting and higher starting torque are required. Contrary to single-cage induction motor which has universally same equivalent circuit, the researchers of the double-cage induction motor introduced several different equivalent circuits for determination of steady-state performance and calculation of design parameters1-18 Uptil 1970 no theoretical or practical work was done for determination of transient behavior of the double-cage induction motor. That year Bandopadhayay11, being the first in this connection, suggested an equivalent circuit for both steady-state and transient analysis and is the same circuit used by Burdi14,15,19. Bandopadhayay also derived a set of differential equations from which both the steady-state and the transient behaviour of a double-cage induction motor could be determined. The same equations were derived independently and used for the prediction of transient behaviour of an experimental double-cage induction motor14. During research it was found that although the total torque predicted by the differential equations was exactly the same as that of the experimental motor, individual predicted cage torques were not true representation of the individual cage torques of the motor. For this reason, entirely new set of differential equations were required since then. Formation of a new set of differential equations for the double-cage induction motor became possible only after the present author wrote a companion paper in which he introduced a direct method of developing differential equations of different machines. Here he describes the direct method to form a new set of differential equations for the double-cage induction motor, which surely remove the disadvantage of previous equations.