Investigation of Squirrel–Cage Induction Motor Properties

Abstract

The assumption is often made when investigating induction motor’s magnetic field that the rotor winding is polyphase and the polyphase current flows in the bars of rotor. The assumption causes difficulties in the evaluation of rotor winding’s geometrical parameters and in the determination of bars location in the slots of the rotor. The geometrical peculiarities of squirrel-cage rotors winding, such as the angle β, are not taken into consideration by the theory of squirrel-cage induction machine given in literature. It is proved that the strength of magnetic field, creating the torque rotating the rotor, depends on the angle β. The expression of resultant torque created by squirrel-cage rotor’s teeth of induction motor has been derived. The two-layer winding of rotor is often used for the wound-rotor induction machines. In this case the angle of rotor winding section’s magnetic axis γ ≠ 0. Though the initial starting torque of induction motor having wound-rotor with two-layer winding is relatively small because the angle γ amounts just 3° – 5°. Meanwhile the angle γ of squirrel-cage rotor’s construction referred in the paper reaches 25° – 35° and therefore the induction motor having the squirrel-cage rotor of described construction creates relatively larger initial starting torque. Ill. 6, bibl. 7 (in English; summaries in English, Russian and Lithuanian).