Electrician Red Seal · Question
A 10 hp, 460 V, 3-phase induction motor is connected to a variable frequency drive (VFD). If the VFD is programmed to operate the motor at 30 Hz (half of its rated 60 Hz frequency), what would be the approximate impact on the motor's power output and cooling capability?
Operating a standard motor at half its rated frequency with a VFD (typically constant V/Hz) means the motor runs at half speed. At half speed, the motor's cooli
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Question: A 10 hp, 460 V, 3-phase induction motor is connected to a variable frequency drive (VFD). If the VFD is programmed to operate the motor at 30 Hz (half of its rated 60 Hz frequency), what would be the approximate impact on the motor's power output and cooling capability?
Answer options:
- Power output would remain 10 hp, but cooling would be reduced. ✅ Both power output and cooling capability would be significantly reduced.
- Power output would be halved to 5 hp, and cooling would be improved.
- Power output would remain 10 hp, and cooling would remain unchanged.
Correct answer: Both power output and cooling capability would be significantly reduced.
Explanation: Operating a standard motor at half its rated frequency with a VFD (typically constant V/Hz) means the motor runs at half speed. At half speed, the motor's cooling fan is less effective, significantly reducing its cooling capability. Also, the power output of an induction motor is roughly proportional to its speed at constant torque, so reducing the speed to 30 Hz will reduce its potential power output significantly.
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