Efficient Electric Motors at Community Motors Inc.
Just glance at some recent headlines about Efficient Electric Motors, energy costs and power shortages. Never has it been more timely to implement prudent use-not repressive use-of electric energy. Come to CMI to learn more.
Efficient Electric Motors in general, and industry’s ‘workhorse’ ac induction motors in particular, represent great potential and realizable energy savings. Electric motors account for more than 60% of the overall electricity consumption by U.S. industry. For other parts of the world and specific industries, the percentage is still higher.
Of course, energy efficiency applies to all elements of a system or process. For example, use of adjustable-speed drives has grown slowly but steadily, bringing dramatic energy savings to applications where variable motor speed is required. But that’s another story.
Management of the motor over its life cycle is also an issue (see later in article).
Many industrial applications run at constant speed and for prolonged periods. This is where motor efficiency can be practical. A point of perspective is that less than 3% of a motor’s life-cycle costs represents purchase price and installation costs-the rest goes to electricity charges. So far, the efficiency focus has been on larger induction motors (M1 hp/0.75 kW), because of the number of motors and operating hours involved.
A different breed
Better design and material content differentiate Efficient Electric Motors from earlier standard models. Quality of manufacturing, such as narrower air gaps between the rotor and stator, also comes into play.
Power losses are inherent in any energy conversion process. More efficient motors reduce losses and have longer lives (see ‘How to…’ sidebar). Efficient design often leads to less temperature rise, which reduces motor maintenance. For example, bearing lubrication and motor insulation lasts longer at lower temperatures. ‘Generally, motor life doubles for each 10 °C reduction in operating temperature,’ according to Rockwell Automation Power Systems (Greenville, S.C.).
A cooler running motor is not always assured. Marv Thomas, product manager, NEMA Frame Motors at Siemens Energy & Automation (Little Rock, Ark.) points out a paradox. Lower total losses in an energy-efficient, fan-cooled motor often permit downsizing of the fan to cut windage losses and fan noise (significant in some applications). But as a result of less ventilation, an energy-efficient motor may not run cooler than a standard-efficiency motor of the same size.
Mr. Thomas verifies the substantial mechanical design needed to raise energy-efficiency of an induction motor. He cites use of more and thinner stator/rotor laminations made of higher grades of steel as important, along with ‘physically more copper’ in the motor windings. He puts the typical added cost of higher efficiency motors in the 17-30% range. Premiums decrease with larger motor sizes.
Life-cycle, total cost views
Baldor Electric Co. (Fort Smith, Ark.) looks at energy-efficiency issues of cost and motor management from the full life-cycle viewpoint. ‘Electricity costs account for nearly 98 percent of the lifetime cost of an electric motor,’ according to the company. ‘Efficiency is critical to long-term economical operation. Modest efficiency improvements yield substantial energy savings.’
Most motor manufacturers have more than one energy-efficient product line. Baldor’s top-of-the-line Premium Efficiency Super-E motor (see lead graphic) has a 1-500 hp size range in the general-purpose version. Efficiency ratings have been raised recently for some 125 models of this line, reaching over 96% at 200 hp and above. The Standard-E line meets efficiency requirements of the EPAct legislation (see below).
At Rockwell Automation Power Systems, ‘total cost of ownership’ for the customer has been a long-standing approach to market energy efficiency. This includes various initiatives to show how energy can be saved and costs associated with power usage reduced. ‘Most customers look for a one-year payback and seek information on which to make a good, sound decision,’ explains Thad Roberts, general products manager, Large AC Motors, at Greenville.
Mr. Roberts mentions an ‘Energy Efficiency Calculator’ tool that can aid the decision process. Available from Rockwell Automation, the software tool calculates comparative motor efficiencies and power savings based on application inputs-prior to the purchase of a motor.
All motor manufacturers include some form of analysis tool to evaluate potential energy savings. Baldor Electric offers its Save Plus software that compares operating costs, shows annual savings, and calculates payback time for specific applications. GE Industrial Systems (Fort, Wayne, Ind.) provides an energy cost calculator for ‘electrical machines.’ Most tools are available online.
EPAct took the lead
Major manufacturers have supplied energy-efficient ac induction motors for a long time. Enlightened users applied these ‘premium’ motors in industries and plants where life- cycle costs justified the higher initial price. However, this left a tremendous number of standard induction motors to consume increasingly precious extra power.
The U.S. has taken the lead to put energy efficiency into legislation as part of wider energy conservation issues. Enacted in 1992, the Energy Policy and Conservation Act (EPAct) finally became effective in October 1997. The U.S. Department of Energy (DOE) enforces the rules of EPAct. Scope of the legislation is limited, but it targets the most numerous motor sizes and types used in industry. EPAct was a groundbreaking regulation for a basic level of motor efficiency.
In essence, EPAct covers NEMA design A and B, three-phase, integral horsepower, general-purpose ODP (open, drip-proof) and TEFC (totally enclosed, fan-cooled) motors with 1,200, 1,800, and 3,600 rpm base speeds in the 1-200 hp size range. IEC equivalent NEMA frame sizes and standard kW power ratings are included because EPAct rules apply to motors imported to North America.
EPAct stipulates allowable nominal full-load efficiency for these motors. Nominal efficiency is the average efficiency of a population of motors identical in design and manufacture. Similar legislation is contained in Canada’s NRCan (Natural Resources Canada) and Mexico’s NOM 74 regulations.
An additional line of energy-efficient motors had to be created by most manufacturers to satisfy minimum EPAct requirements. Of course, government regulation of any business activity or equipment sourcing brings its share of negative user response. Still, EPAct is a step forward. Read More
