AC Motor Efficiency - A Guide to Energy Savings
What we have done, and what we are doing
Part 4: MOTOR LABELING | Efficiency as a Range of Numbers | Reliance Duty Master XE Motors | Efficiency as a Range of Numbers The purpose of indicating the efficiency on a motor nameplate is to inform the buyer so that the most efficient motor can be selected for a given application. When a single unique number is used, a buyer is not sure whether that number is a minimum, average, or maximum efficiency value. Nor is there any guarantee that the stated value is the actual efficiency of any or all motors in that rating. The buyer also has no idea of how the efficiency was determined. Further, a unique number connotes exactness - a specified efficiency value which requires each motor of a given design to be individually tested. Since motors are sample tested on a statistically valid quality control schedule, and are also subject to variations in manufacturing methods and raw materials which result in variations in watts losses affecting efficiency, it is not reasonable to state efficiency as a single number, without qualification. Consistent with NEMA’s Energy Management Committee Proposal, NEMA Suggested Standard MG 1-12.58.2 was adopted and calls for the efficiency of polyphase motors 1-125 HP to be identified on the motor nameplate. Reliance was the first motor manufacturer to adopt the NEMA standard, and in June, 1977, implemented the NEMA motor efficiency labeling program and supported efforts to adopt a revision to this Suggested Standard. This standard MG 1-12.58.2 calls for the nominal efficiency of polyphase motors 1-125 HP to be identified on the motor nameplate (Figure 11). Because the NEMA standard is based on testing motors according to a statistically valid sample, the NEMA/Reliance Efficiency Table (Figure 10) includes both a nominal and a minimum full load efficiency value expected from a large population of motors of a given motor design. The nominal efficiency value represents a value not greater than the average efficiency of a large population of motors of the same design. The minimum value is the lowest efficiency allowed for a motor of specific design within a designated efficiency band. Reliance guarantees full load efficiencies an efficiency band higher than NEMA standards require. In addition, Reliance recommends that energy efficiency evaluations be based upon full load guaranteed efficiencies established in accordance with NEMA standard MG 1–12.58.1 and that these efficiencies be NEMA values as defined in table 12-8.
Figure 10
RELIANCE ELECTRIC
During August, 1977, Reliance introduced a High Performance design of energy efficiency motors which stressed several performance factors, in addition to high efficiency, and was aimed at the motor user who seeks premium motor value. In 1979 Reliance introduced a new family of energy efficient motors 1-1/2 to 200 HP designed as "XE" that reduced energy losses by as much as 50% over standard industrial designs
Figure 12
These energy efficient motors can reduce power consumption significantly so operating costs savings can more than offset their initial price premium. The following table (Figure 13) illustrates the annual savings of 1800 RPM designs 3-300 HP XE vs. standard industrial designs based on $.08 per kilowatt hour, 7,200 hours of operation per year.
Figure 13
The reduction of watts loss, as much as 50 percent, is achieved by optimized design, improved material selection and quality control in the five areas of watts loss in an AC motor, as Figure 14 illustrates.
Figure 14
|
|||||||||||||||||||||||||||||||||||||||||||||||||
| Copyright ©2007, Baldor Electric Company.
All Rights Reserved. |