In slip-ring, induction motor rotor circuit can be opened. Under this condition, when stator is connected to three-phase supply, it draws a very small current called no-load current I0. This current has two components, that is,working component Iw and magnetizing component Imag. Working component is in phase with the supply voltage, and it supplies the stator iron losses. Whereas magnetizing component lags behind the supply voltage V by 90° and produces the mutual flux that links with stator and rotor winding and induces E1 and E2s.
The equivalent circuit and phasor diagram of the motor under this condition is shown in Figure 12.16.
Fig. 12.16 (a) Equivalent circuit of an induction motor with open circuited rotor (b) Phasor diagram of an induction motor with open circuited rotor
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