When electricity was cheap, efficiency was not necessarily top of mind for many. However, current energy prices force manufacturers to further analyze where they use energy and how they spend their energy dollars.
According to NEMA, electric motor and generator driven systems account for nearly 70% of the electricity consumed in the U.S. industrial manufacturing sector. Thanks to leading motor manufacturers and groups such as Motor Decisions Matter, manufacturers are beginning to replace motors with NEMA Premium motors, improve rewind practices and follow U.S. Department of Energy and Electrical Apparatus Service Association best practices.
However, some manufacturers are still using EPAct and pre-EPAct motors. Some manufacturers and OEMs are still applying larger motors than loads require, which is extremely inefficient. Some are still starting motors that could be used with soft starters or adjustable speed drives across the ac line.
Too large for the load
Many of the motors in operation today in the U.S. are larger than they have to be. Many motors are loaded at less than 50%. However, they use almost as much electricity at lighter loads as they do fully loaded MDASSML an expensive mode of operation. Appropriately matching the motor and its load produces savings that add directly to the bottom line.Too large for the load
Tim Albers, director of marketing, Emerson Motor Co., St. Louis described a scenario where a facility wanted to upgrade to Premium Efficiency motors. According to Albers, many of their motors had been there 30 to 40 years. “More than half of their motors were 50% loaded or less. In many cases, the actual load on the belt was 15 hp MDASSML and they were using a 50 hp motor!”
For this application, Albers explained a 20-hp motor provides a 25% safety factor; 25 hp provides a 40% safety factor. “Do they think they need more than 40%? No, they had a 150% safety factor on this motor!”
Motors designed into original equipment are typically ‘right sized’ if the OEM is following best practices. Albers said companies such as Ingersoll Rand, ITT Goulds and Flowserve have the tools in place to do an appropriate job. “When ITT Goulds or Flowserve is sizing a pump motor, or Ingersoll Rand is sizing a compressor motor, they understand that they’re sizing motors between 75% or 80% to 105% of rated horsepower. They know exactly what they’re doing. They know whether they need the extra safety factor or not. They know the questions to ask to get a correctly sized product,” Albers said.
Not all end users fall into the inefficient category. “The same thing I said about the large OEMs is also true about the large end users,” Albers said. “There are guys who have written papers about efficiency in their operation; they know exactly what’s going on. They are sizing them %%MDASSML%% because they know that as long as they are at 70% loading or more, they are getting the full efficiency of the product MDASSML and they know exactly where they are going with it.”“The biggest issue we run into is when people who are not experienced try to size a motor or choose a motor for an application,” Albers continued. “The biggest issue is either smaller manufacturers or end-user maintenance personnel who say ‘I had a 40 hp, it failed, why don’t I put a 50 hp on this time?’ That 40 hp (motor) might have lasted 12 or 14 years, which is an appropriate life of the motor. Upsizing the motor may or may not be a good thing. For efficiency, it’s probably a bad thing.”
Right-size the motor for the load
“Reduce system load,” said John Malinowski, product manager, ac and dc motors, at Baldor Motors and Drives, speaking at the Plant Engineering Manufacturing Summit in Chicago. “In the U. S., we always think bigger is better. Well, it isn’t. You need the right size. Motor downsizing is on the DOE list. I don’t like calling it ‘downsizing;’ I like to call it ‘right-sizing.’”
“Match the equipment to the load,” continued Malinowski. “Something as simple as going to one of these notched V-belts, instead of a solid V-belt, can add 3% to system efficiency.”
To optimize efficiency, determine whether the specific torque capabilities of a motor meet the torque requirements of the application’s load. Although motors that operate with constant flux are said to have constant torque, the demand of the load determines the actual amount of torque produced. Compare the motor’s speed-torque curve with the load’s speed-torque requirements.
Motor manufacturers supply torque characteristics for the motors they manufacture. NEMA’s publication MG 1 is another good source for this information. The most accurate way to obtain torque characteristics of a given load is to obtain them from the equipment manufacturer.
