
Induction Motors - Rotating Field, Slip and Torque 157
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Figure 5.8 Phasor diagram under no-load conditions, showing magnetizing
current I
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Viewed from the supply the stator looks more or less like
a pure inductance, a fact which we would expect intuitively
given that - having ignored the rotor circuit - we are left
with only an arrrangement of flux-producing coils sur-
rounded by a good magnetic circuit.
Summary
When the stator is connected to a three-phase supply, a
rotating magnetic field is set up in the air-gap. The speed of
rotation of the field is directly proportional to the frequency
of the supply, and inversely proportional to th ...