Performance of Polyphase Induction Motor Without Loading

Author: E.E. Kimberly

The approximate characteristics of a polyphase induction motor may be found without the necessity of loading. It is possible to construct a circuit of resistances and reactances in a series and parallel combination such that, when one of the elements is varied, the current variations simulate those in an induction motor. Such a circuit, which is shown in up, but is shown to justify the vector diagrams of Figs. 18-14 and 18-15. The quantities R₁, X₁, R₂ and X₂ of the motor are also in its equivalent circuit; but RL is a variable resistance in the circuit whose variation may be made to simulate a variable load on the motor. The vector diagram and locus resulting from changes in the motor load is called the circle diagram of the motor.4

Fig. 18-15. Circle Diagram for Example 18-2