25-04-2012, 01:22 PM
Torque Production
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Principles of Torque Production
In the earlier section, we saw how a rotating flux is produced. Now let us consider a rotor,
which is placed in this field. Let the rotor have a coil such that the coil sides are placed
diametrically opposite each other. This is shown in the fig. 1. Since the flux generated by
the stator rotates flux linked by this rotor coil also changes.
At t = 0, one can see that current in a phase coil is at negative maximum, while b and
c phases have positive current of 0.5 units. Now if we consider the current flux profiles at
coil sides a, b′ , c, the picture that emerges is shown in fig. 8.
Since main flux at the a coil side is close to zero, there is very little torque produced
from there. There is a tendency to move due to the b′ and c coil sides, but they are in
opposite directions however. Hence there is no net torque on the rotor. This brings up
another important conclusion — the resistance of the rotor is an important part of torque
production in the induction machine. While a high resistance rotor is better suited for torque
production, it would also be lossy.