Premium Motor Efficiency: Taking Care Of The Latest And Greatest
This article first appeared in IMPO's March 2013 issue.
Motors are well-known in the industry as huge users of electricity. Electric motor-driven systems are everywhere: powering a small office cooling fan or creating the energy needed to move the conveyor that runs the entire length of a warehouse. In U.S. factories, these motors account for over 60 percent of the total energy consumed – and 25 percent of the total energy used in the United States overall – a staggering amount of energy that is worthy of a second look to be sure your facility is maximizing its motor performance.
A More Efficient Motor
Due to the costs of running an electric motor, and growing legislation, industrial motor manufacturers are continually striving to create the latest and greatest in efficient motors. “For industrial motors, the biggest evolution has been in efficiency,” says Tim Albers, director of marketing, Nidec Motor Corporation. “North America is leading the way with legislated NEMA Premium® efficiency levels, which equates to IE3 (premium efficiency standard) for the IEC standard for the rest of the world,” he says, “but countries and regions around the world are moving toward IE3.” This shift means major mechanical changes for motors.
“The growing addition of grounding rings to industrial electric motors to ‘short circuit’ the motor and take voltage off the shaft and protect the motor bearings when used on an inverter is a major change,” Albers explains. In the past, the use of shaft grounding devices on a motor was not very common, but its use has accelerated in the last few years. Adding grounding rings to an electric motor potentially extends the motor’s uptime and increases productivity by channeling harmful electrical currents away from bearings to ground, mitigating electrical bearing damage that may eventually result in motor failure and is “one way that motor and drive performance continues to improve,” he explains.
The growing addition of grounding rings in the U.S. market continues to accelerate this trend. Albers adds, “At least three component suppliers have entered the grounding ring market as suppliers to the industry.”
Another change that helps motor life is a cooler running motor. Albers explains, “The higher the temperature of a motor, the lower the corona inception voltage and therefore the shorter the life of the winding.” Corona inception voltage (CIV) is a measure of the ability of a motor’s windings to withstand voltage stress. The move to higher efficiencies has led to lower temperature rise in many industrial motors, “particularly motors that are general purpose and have traditionally been purchased based on price.” Albers adds, “Many of those motors have significantly lowered temperature rise now that the product has moved from standard to EPAct (Energy Policy Act) to now NEMA Premium efficiencies” – the result of growing legislation.
In 1992, Congress, as part of EPAct, set minimum efficiency levels for electric motors in response to a worldwide movement for energy conservation. This legislation was followed in 1998 by a voluntary agreement of motor manufacturers to follow three efficiency classes: standard, improved, and high efficiency; this agreement was issued by the European Committee of Manufacturers of Electrical Machines and Power Systems. And the Energy Independence and Security Act of 2007 (EISA) is the most recent energy law to go into effect. The National Electrical Manufacturers Association (NEMA) participated in crafting critical provisions of EISA and focused on new motor efficiency regulations and now, “any equipment sold in the U.S. for use here needs to have compliant motors,” says John Malinowski, senior product manager – AC motors, Baldor Electric Company. “Some foreign manufacturers have not been able to meet the higher efficiency levels and have withdrawn from U.S. sales.”
But those motor manufacturers who have been able to meet ever-increasing efficiency demands have continued to create motors with new, efficient technologies. “New technologies with efficiency beyond conventional AC squirrel case induction motors are being introduced,” Malinowski explains, “such as interior permanent magnet, switched reluctance, and synchronous reluctance.” He includes that all of these have efficiencies higher than what is possible with conventional induction motors and are smaller in size in most cases. Today, “we have motors now that have efficiencies above 96 percent.”
Improving Motor Performance
For those hoping to use motor drives to gain even more operational efficiency, Malinowski explains that is a common misconception. “The motors do not gain efficiency when used with drives,” he explains, “they actually are slightly less efficient because they are no longer operated from a sine wave power supply.” The drive produces direct current for motor operation and “it is the use of the motor in an adjustable speed operation that is more efficient – particularly on a centrifugal load such as a fan or pump,” he says. As speed is decreased, the horsepower required to drive the pump drops by the cube of the speed change. “On constant torque applications such as conveyors,” Malinowski adds, “an adjustable speed system could add to efficiency by improving the plant’s productivity if one were to look at widgets produced per kWh.”
“A motor cannot usually be made more efficient than what was originally done by the manufacturer,” he explains. “There is no extra room in the slot for additional copper windings these days.” But he adds that maintenance can ensure that an efficient motor is operating at its design points.
Do not “undersize motors where they operate in their service factor,” Malinowski says, which can be a common practice on compressors.
Albers agrees: “Size the motor correctly for the load; a severely over or under loaded motor significantly lowers efficiency.”
“If a NEMA Premium motor is already installed,” says Albers, “then have a plan with your service repair facility on what will be done with that motor to maintain its efficiency upon repair.” A facility’s maintenance program can optimize motor efficiency and maximize uptime by also having a plan in place for the replacement of all motors in service that includes the exact model of the NEMA Premium motor that will replace what is currently installed. Albers offers a few tips to help manufacturers choose wisely when it comes time to replace an existing motor:
- Check the max and average loading of the motor to determine an accurately sized motor when a replacement is needed. “Using amps versus full load amps and correcting for voltage is a pretty good proxy,” he adds.
- Choose a NEMA Premium motor. While some variation exists among motor manufacturers, “you cannot go wrong by always specifying a NEMA Premium product,” says Albers.
- Be aware of mechanical components losses. A NEMA Premium motor will optimize efficiency in terms of the motor, but low efficiency gearing or belting will adversely affect system efficiency. “We need to look at system efficiency for the highest gains rather than component replacement,” stresses Malinowski.
Maintenance might create the most efficient motors unless a technological motor breakthrough occurs: “I think the age of dramatic motor changes will only occur with an advent in new technology beyond IGBT inverters and induction motors,” says Ablers, “exactly what that will be is still to be determined.”
But one thing is certain, adds Malinowski, “more premium motors are being built for sure.”