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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 400 V DC source and draws 40 A armature current. A linear magnetic circuit. The external resistance, in Ω, that must be connected in series with the armature to reduce the speed of the motor by half, is closest to
- 23.28
- 4.82
- 46.7
- 0
Correct answer: 23.28
Solution
To reduce the speed of a DC series motor by half, the armature voltage must also be halved, which requires adding external resistance to drop the voltage across the armature. The calculated resistance of approximately 23.28 Ω accounts for the necessary voltage drop while considering the motor's characteristics and the load torque relationship.
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