In case of a Squirrel-cage induction motor using three-phase bridge inverter, which one of the following statements is correct for speed control?

Question

Question

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UPSC IES Electrical 2022 Prelims Official Paper

if frequency increases, then starting torque decreases with constant supply voltage.
if frequency increases, then starting torque increases with constant supply voltage.
if frequency decreases, then starting torque increases with constant supply voltage.
both (a) and (c)

Answer 1

Solution:-
In an induction motor, approximate torque eqⁿ considering stator impedance is negligible is given below:-

At starting, s = 1

∴

∴ x ∝ f

∴

given voltage is constant

∴

Hence, if frequency increases, then starting torque decreases and if frequency decreases, then starting torque increases.

Hence, both option 1 and option 3 are correct.

The correct answer is option "4"

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