A study of the power angle concept of polyphase induction machines

Abstract

With the aid of field maps and the basic fundamental equations related to polyphase induction motors, a torque angle is defined on a vector diagram. The electromechanical torque developed by the rotor, the stator or input current, the rotor current, the slip, and the induced voltage in the rotor are evaluated as functions of this torque angle for normal operation of polyphase induction machine. Other operating characteristics including input power, power factor, and efficiency are obtained using the power angle concept. This torque angle is found to be analogous to the one defined for synchronous machine. A mechanical equivalent circuit of polyphase induction machine is also established. For electromechanical transient behavior after a load change, differential equations have been set up and solved by utilizing the torque angle concept and the mechanical equivalent circuit of polyphase induction machine. The performance characteristics of the synchronous-tie are also obtained by using the power angle concept. Experiments were performed on a phase wound rotor induction machine and the results were compared with those of the power angle concept. The power angle concept has thus been extended from synchronous machines and single phase induction machines to polyphase induction machines.