Final answer:
General purpose NEMA motors are rated to operate at 10% of the rated voltage for efficiency and durability. High-performance motors, with higher efficiency ratings like 90% for a 100-hp motor, save energy and costs. Calculations for motor operation like resistance and back emf are based on Ohm’s law.
Step-by-step explanation:
Most general purpose National Electrical Manufacturers Association (NEMA) motors are rated to operate within 10% of the motor's rated voltage to ensure efficient performance and longevity. This rating is crucial because operating a motor at the correct voltage ensures that it performs effectively and also prevents undue stress on the motor's components which could lead to premature failure.
Utilizing high-performance motors is important because they have higher efficiency rates. For instance, a 100-hp motor can have an efficiency of 90%, and a 1-hp motor can have an efficiency of 80%. High efficiencies mean less electrical energy is wasted, which leads to cost savings over time, as well as a reduced environmental impact due to less energy consumption.
Answering a question about the necessary operating voltage for a general-purpose motor involves calculations based on Ohm’s law and understanding the concept of back electromotive force (back emf), which opposes the supplied voltage. For an operational example: a motor operating on 240 V electricity might have a 180 V back emf at operating speed, and if it draws a 12.0 A current, the resistance can be calculated using the formula V = IR.