The Efficiency of AC Motors: Past, Present, and Future

While electric motor technologies began emerging in the 1820s, they didn't make their way into industry until 50 years later. Furthermore, they didn't become the industry standard until well into the 20^th century. Then came the energy crisis of the 1970s.

Oil prices jumped a whopping 350% during the energy crisis, causing massive disruptions throughout the world economy. Increasing energy efficiency became a major topic of discussion in the industry. Many governments and large corporations made a big push to design new, more efficient products across the board – including electric motors.

Efficiency Standards

Since the 1980s, governing bodies and organizations have released standards for electric motor efficiency. As the top manufacturers in North America serve both Canada and the United States, some of the standards we discuss below will be US-based. Canadian industry still strives to meet and exceed these standards.

• Consortium for Energy Efficiency: Seven utilities and advocacy groups joined forces in 1991 to create the Consortium for Energy Efficiency. The CEE's goal is to influence national markets, large corporations, and governments to encourage a focus on and movement towards energy efficiency. CEE has created efficiency programs for individual industries as needed.
• EPAct 1992: The first notable release of electric motor efficiency standards was through the Energy Policy Act of 1992, an act by the United States government. EPAct established efficiency standards for a variety of industries, including electric motors and their use.
• NRCan: Natural Resources Canada regularly releases federal Energy Efficiency Regulations to set minimum energy efficiency levels for products. Products must meet these regulations to be manufactured in or imported into Canada. Currently, NRCan's regulations for electric motors are that of the NEMA Premium® standard.
• NEMA: The National Electrical Manufacturers Association was founded in 1926 to create a space for members to discuss and solve industry-wide concerns. They released their NEMA Premium® efficiency motor program in June of 2003. The program became the gold standard for electric motor efficiency.
• EISA 2007: The Energy Independence and Security Act of 2007 mandated that all motors imported or sold in the US must be Premium Efficient as of Dec 2010.
• IEC: In 2008, the International Electrotechnical Commission published the new Super-Premium Efficient standard to encourage manufacturers to keep striving for more efficient motor designs.

Why Focus on Efficiency

First, let's start with some surprising stats:

• Motors and the equipment they drive account for 63% of the total energy consumed in the industrial sector. That is 25% of the total energy consumed. (US stat)
• The purchase price of an electric motor only accounts for 3% of its total lifetime costs. The remaining 97% is electricity (and a small fraction for maintenance).
• A 1% increase in efficiency to each motor in North America would lead to a cost savings of up to $1.4b yearly! (US stat)
• Companies that develop and implement a motor efficiency program generally uncover a cost savings of 33%.

It's clear to see that you would want to increase the energy efficiency of the electric motors you use for various reasons. For many businesses, the sole basis of cost savings is big enough to make the change. However, the benefits of reduced downtime, a smaller carbon footprint, and increased equipment reliability should garner buy-in for everyone else.

Efficiency Losses

Electric motors are energy conversion devices, converting electrical energy into mechanical energy. Energy conversions are rarely, if ever, perfectly efficient; there are always energy losses in some form, usually to heat.

Motor efficiency is the measure of the difference between power consumed and power available at the output shaft. Here are the ways energy is lost along the way:

• Power Losses: Heat generated by resistances in the stator windings and conductive rotor plates.
• Rotor Slip: The difference between the RPM of the rotor and the rotational speed of the magnetic field.
• Magnetic Core Losses: Hysteresis effect, eddy currents, and magnetic saturation.
• Friction: Resistance creating heat losses.

Finding solutions to these efficiency losses has proven fruitful; manufacturers are constantly innovating and designing more efficient motors. Most of these efficiency losses can be cured with improved design and more premium materials.

Premium Efficient Motors

One brand didn't wait until the Energy Crisis to start looking into ways to increase efficiency. Baldor-Reliance began working on improving the efficiency of their motors 100 years ago in the 1920s. They're an industry leader in developing new technologies improving motor reliability. And were the first electric motor brand to release a premium efficient motor.

The Super-E Premium Efficient motor by Baldor was born in 1983. This motor became the first electric motor brand to be recognized by The Consortium for Energy Efficiency because of their impressive efficiency ratings.

Electric motors rated as Premium Efficient meet or exceed the NEMA Premium® efficiency standards. It should be noted that not all manufacturers submit their designs for an efficiency rating. As such, many motors may not sport the NEMA Premium® efficiency logo but may meet the standards.

Severe Duty Efficient Motors

More electric motor manufacturers have crossed their energy efficiency upgrade over from their general purpose motors to their severe duty motors in recent years. You'll find many severe duty motors on the market. All are capable of handling harsh environments, high altitudes, and other extreme conditions, all while offering the efficiency of NEMA Premium® efficient motors.

Ultra-Premium Permanent Magnet Three-Phase Motors

The strive for Super-Premium efficient motors pushed manufacturers out of the box with their designs. Increasingly more efficient motors are released to market every year. One such motor is the Ultra-Premium Efficient permanent magnet three-phase motor. Massive improvements in materials technologies and improved inverter compatibility have moved these motors to the front of the electric motor efficiency race, with ratings that far exceed the NEMA Premium® efficiency standards.

"These include more energy-dense permanent magnets, new electromagnetic topologies for three-phase permanent magnet motors, availability of lower-loss electrical sheet steels, improved inverter control algorithms in commercial off-the-shelf variable frequency drives (VFDs), improved thermal management materials and systems, and the improved performance and packaging of semiconductor switching devices for the inverters."

(Source: Advanced MotorTech LLC)

Efficiency Improvements/Developments

With all this talk about efficiencies and improved motor designs, you're likely wondering what electric motor improvements have come about.

• Bearings: Bearings are the number-one mechanical reason for motor failure. This failure often comes from stray currents on the shaft, which can be mitigated by switching them out for insulated bearings and installing shaft grounding rings. Another reason for failure is poor-quality grease. This can cause friction and the loss of power to heat. However, these problems can be mitigated by regular maintenance and using the adequately rated grease for the application.
• Grease: Polyurea grease is becoming a standard for electric motor bearings. This type of grease outperforms the competition. It is more durable to mechanical shearing forces and has an additive that is more resistant to washout, rust, and corrosion.
• Copper: More copper has been added to the rotor to increase electrical conductivity, lower operating temperature, reduce weight and size, and extend the motor's life.
• Windings: The grade of the materials used in the windings has increased. Allowing for better conductivity, reducing heat losses due to resistance.
• Steel: Upgrade laminations to premium-grade steel.
• Updated Design: Precision air gaps between rotor and stator means lower resistance and better cooling capabilities.
• Inverter Protection: With the increasing use of VFDs, motor manufacturers are now designing motors with built-in inverter protection to mitigate voltage spikes from the controller.
• VFDs:Variable Frequency Drives are being used more and more in industry, and it's no wonder why. VFDs help manage motor efficiency by providing the exact amount of power needed while mitigating any power issues from source. Meaning less energy is lost, and the motor runs smoothly and reliably.

Payback Calculators

Sometimes it's hard to make the decision to buy into a new program, especially one where the initial investment is higher than if you were to stick to the status quo. Premium Efficient motors are often more expensive than their standard efficient counterparts. That certainly doesn't mean they aren't worth the investment.

You can use a motor efficiency payback calculator to determine if the investment is worth it for your business. A payback calculator will tell you how many months it will take for the energy cost savings of a new premium efficient motor to equal and surpass that of the old standard efficient motor. The payoff can come in as little as a few months for some motors and continue over the motor's lifetime.

Are you ready to save on energy costs?

You don't have to wait for your motors to break down before looking into more efficient models. The cost savings from switching to premium efficient motors will bring such savings on power costs that it's worth making the switch now.

Summary

To save, or not to save? Energy efficiency isn't just a buzzword; it's an initiative that can directly impact your bottom line. Take advantage of the advances in technology and electric motor design to save more money, decrease downtime, and increase the reliability of your valuable equipment.

Interested in speaking to a technical expert to see if switching over to premium efficient motors is worth it for your business? Get in contact with us today; we're ready to get to work on your electric motor project.