GATE EE 2017 Set 1 — Question 45
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Electrical Machines → Single-Phase Induction Motors → Starting Methods
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Question
A 375 W, 230 V, 50 Hz, capacitor start single-phase induction motor has the following constants for the main and auxiliary windings (at starting): (main winding), (auxiliary winding). Neglecting the magnetizing branch, the value of the capacitance (in ) to be added in series with the auxiliary winding to obtain maximum torque at starting is ________.
Correct answer
145 to 155
Solution
The starting torque of a single-phase induction motor is proportional to .
Let be the capacitive reactance added. The new auxiliary winding impedance is .
To maximize , we differentiate with respect to and set to zero:
Given , , , , .
.
The value lies in the range 145 to 155.
Let be the capacitive reactance added. The new auxiliary winding impedance is .
To maximize , we differentiate with respect to and set to zero:
Given , , , , .
.
The value lies in the range 145 to 155.
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