A review of methods of starting induction motors

The normal methods of starting induction motors are well known but the theory of these methods is usually taken for granted. This paper is an attempt to supply in simple form a practical theory directly applicable to the majority of everyday problems and compare the various methods of starting commonly employed. Theoretical accuracy has been sacrificed to practical utility and simplicity. It is hoped that the result will appeal to the practicing engineer. The stickler for accuracy and mathematical exactitude is warned that this paper is not for him. The general induction motor theory is reduced to a theory of the rotor current and torque. Direct-on-line and star-delta starting are considered and the load-torque-speed limitation of the latter noted. Devices for use in the stator circuit are reviewed in some detail and compared. Devices for use in the rotor circuit are similarly reviewed and compared. Finally, a new method of designing a rotor starting resistance is described.