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Understanding Premium Efficiency Motors

Dec 2, 2016

After the rise in energy conservation awareness around the globe, the US Congress established minimum efficiency levels for electric motors in their 1992 Energy Policy Act (EPAct). In 2007, the Energy Independence and Security Act (EISA) was signed into law. The National Electrical Manufacturers Association (NEMA) took an active part in providing EISA with increased motor efficiency levels. As a result, new motor efficiency regulations were made for general purpose electric motors, and some categories of definite/special purpose electric motors.

How NEMA Defines Premium Efficiency

As part of the EISA initiative, the NEMA Premium efficiency motor standard was introduced to:

1. Reduce energy operating costs of electric motors on industrial & commercial buildings

2. Help purchasers find higher efficient motors that save money & improve system reliability

3. Optimize efficiency in motor systems regarding power supply & utility deregulation issues

4. Reduce energy consumption & pollution associated with electrical power generation

NEMA Premium standards bring a new question to electric motor purchasers: Are the motors you’re buying as efficient as they could be? Or are your motors wasting energy and money?

How to Determine Motor Efficiency & Energy Loss

In order to determine the efficiency of an electric motor, you must find the ratio of usable shaft power to electrical input power.

shaft power (HP) ÷ input power (HP) = motor efficiency (%)

Shaft power is the energy a motor transfers to drive a machine. Input power is the energy a motor pulls from a power supply (the energy that costs money). In order to determine loss in motor efficiency, you must determine the difference between a motor’s input power and shaft power.

input power (HP) – shaft power (HP) = losses of electric motor power (HP)

What might be causing your electric motor’s loss in efficiency? Below are some of the most common factors that cause energy/power loss in an electric motor:

  • Loss from the coil winding (resistance)
  • Loss in the rotor bars & slip rings
  • Loss due to magnetizing of the iron core
  • Loss from friction of bearings

How Premium Efficiency Motors Conserve Energy

In order to minimize and balance the common energy/power losses listed above, premium efficiency motors must be designed by manufacturers who have plenty of knowledge and experience in test facilities with precision instrumentation.

Premium efficiency motors are designed by including more iron and copper material than is used on standard electric motors. As a result, premium efficiency motors are typically larger and heavier than standard electric motors. Other common characteristics of premium efficiency motors include:

  • Higher slot fill in the copper winding
  • Thinner laminations of improved steel properties
  • Reduced air gap
  • Optimized cooling fan designs
  • Special & improved bearings

Copper is a valuable material in a premium efficient design because it produces higher electrical conductivity compared to other metallic conductors. Manufacturers can increase a motor’s electrical energy efficiency if they increase the mass and cross section of copper in its coil winding.

Premium Efficiency Motor Advantages

According to the U.S. Department of Energy, it would only take ten years for the NEMA premium efficiency motor program to:

  • • save 5.8 terawatts of electricity
  • • prevent ≈80 million metric tons of CO2 from being released into the atmosphere

To put this into perspective, the results would be the same as keeping 16 million cars off the road.

Energy & Cost Savings

Electric motor systems are responsible for consuming 40% of the world’s electricity to drive compressors, pumps, and fans, and other mechanical applications. Premium efficiency motors can help to significantly lower global greenhouse gas emissions.

However, motor buyers generally concentrate on price, not electricity consumption. What some buyers don’t know is that, because energy accounts for over 97% of a motor’s total lifetime operating costs, improvements in efficiency could bring enormous savings on energy and cost. If you pay a little more money upfront for a premium efficient motor you’re sure to receive significant payback in energy savings.

Ready to save money on lifetime operation costs and reduce energy consumption with your electric motor systems? Contact us to learn more about your premium efficiency motor options.