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DC motor speed control

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A separately excited dc motor is running at 500rpm, driving a load whose torque is proportional to the speed, the motor armature voltage is 220V and the armature current is 20A. What resistance should be inserted in the armature circuit to reduce the motor speed to 250rpm? The armature resistance is 1 ohm.

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Detailed step by step solution provided. A problem on speed control of DC motors are determined.

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A separately excited dc motor is running at 500rpm, driving a load whose torque is proportional to the speed, the motor armature voltage is 220V and the armature current is 20A. What resistance should be inserted in the armature circuit to reduce the motor speed to 250rpm? The armature resistance is 1Ω. (Ans: 11Ω)

Solution : Power output of the motor = P = Torque x Angular speed = τω .......(1)

As torque is directly proportional to speed, τ = Kω ...

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