GATE EE 2017 Set 1 — Question 47
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Electrical Machines → DC Machines → Speed Control & Starting
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Question
A 220 V DC series motor runs drawing a current of 30 A from the supply. Armature and field circuit resistances are and , respectively. The load torque varies as the square of the speed. The flux in the motor may be taken as being proportional to the armature current. To reduce the speed of the motor by 50%, the resistance in ohms that should be added in series with the armature is ________. (Give the answer up to two decimal places.)
Correct answer
9.5 to 12
Solution
1.Initial state: V, A, .
V.2.Given and . Since , we have .
3.New speed A.
4..
.V.
5..
..
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