Among available 5 HP, 50 Hz, 3-phase, 440 V induction motors of various RPM ratings, which one is the most expensive ?
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Answer: A. 730 r.p.m.
Explanation
Lower synchronous speed motors require a greater number of magnetic poles for a fixed frequency. Manufacturing motors with more poles demands larger physical frames and significantly more copper windings. Increased material usage and complex manufacturing processes make low RPM induction motors much more expensive. Synchronous speed equals one hundred twenty times frequency divided by the number of motor poles. Motor physical size scales directly with torque requirements and inversely with operating speed. Higher pole counts require intricate internal wiring patterns that increase labor costs during production.
Industrial machinery often selects high-speed motors paired with gearboxes to reduce initial equipment costs. Purchasing heavy duty equipment requires balancing upfront motor costs against mechanical transmission efficiency. Specialized low-speed drives are chosen only when direct drive mechanics are strictly necessary. Option b features a higher RPM rating, requiring fewer poles and lower manufacturing expenses. Option c features an even higher RPM rating, resulting in a smaller physical frame size. Option d features the highest RPM rating, making it the most compact and least expensive option.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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