In a three-phase induction motor which component represents mechanical load in the equivalent circuit?

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  1. R2 (1 - s)
  2. \(\rm \frac{R_2(1-s)}{s}\)
  3. \(\rm \frac{sR_2(1-s)}{s}\)
  4. \(\rm \frac{R_2}{s}\)

Answer (Detailed Solution Below)

Option 2 : \(\rm \frac{R_2(1-s)}{s}\)
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Detailed Solution

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Equivalent circuit of a 3ϕ induction motor

The total resistance at the rotor is represented as \(\rm \frac{R_2}{s}\) where s is the slip.

Now, if we create an equivalent transformer circuit for an induction motor, the secondary resistance will be R2. Thus, the load resistance will be \(\rm \frac{R_2(1-s)}{s}\).

Induction motor modelled as a transformer:

qImage68135ecd00709ffd3bc562e7

When all the rotor parameters are shifted to the stator side induction motor circuit is given by:

qImage68135ece00709ffd3bc562e8

\(\rm \frac{R_2(1-s)}{s}\) is the resistance that represents mechanical load in the equivalent circuit.

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