GATE EE 2025 Set 1 — Question 44
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Electrical Machines → DC Machines → Speed Control & Starting
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Question
A DC series motor with negligible series resistance is running at a certain speed driving a load, where the load torque varies as cube of the speed. The motor is fed from a DC source and draws armature current. Assume linear magnetic circuit. The external resistance, in , that must be connected in series with the armature to reduce the speed of the motor by half, is closest to
Correct answer
(A) 23.28
Solution
1.Torque Relationships:
- Load torque .
- Motor torque . For a linear magnetic circuit, , so .
- At steady state, .
- , , .
- Since is negligible, .
- .
- .
- .
- .
- .
- .
- .
- .
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