- In the low horsepower range, the induction motor is being challenged by permanent magnet and reluctance motors which have higher efficiency.
- These advanced motors do not have losses in the rotor and feature higher torque and power/weight ratio.
- Efficiency improvements can reach 10%–15%, compared with single- phase induction motors for small scale motors.
- Compared to the shaded-pole motors commonly used in small fans, these types can more than double motor efficiency.
Motor Speed Controls - AC induction and synchronous motors are essentially constant-speed motors. Most motor applications would benefit if the speed could be adjusted to the process requirements.
- The potential benefits of speed variation include increased productivity and product quality, less wear in the mechanical components, and substantial energy savings.
- In many pump, fan, and compressor applications, the mechanical power grows roughly with the cube of the fluid flow; to move 80% of the nominal flow only half of the power is required.
- Conventional methods of flow control have used inefficient throttling devices such as valves, dampers and vanes. These devices have a low initial cost, but introduce high running costs due to their inefficiency.
- Use only the power that’s needed.
Multi-Speed Motors - In applications where only a few operating speeds are required, multi-speed motors may provide the most cost- effective solution.
- These motors are available with a variety of torque- speed characteristics.
- Motor systems are often oversized as a result of the compounding of successive safety factors in the design of a system .
- The magnetic losses, friction, and windage losses are practically constant as a function of the load.
- Therefore, motors which are oversized (working all the time below 50% of capacity) present not only lower efficiency but also poor power factor
- Efficiency drops significantly when a motor operates lightly loaded (below 40% ).
- The power factor drops continuously from full load.
- It is essential to size motors correctly and to identify motors which run
grossly under loaded all the time.
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