PUSHING MOTOR EFFICIENCY TO THE LIMIT

Transcription

1 PUSHING MOTOR EFFICIENCY TO THE LIMIT Federal legislation mandating energy efficiency standards promise more reliable electric motors and lower operating costs for equipment manufacturers A Reliance E!ecW employee at the Cleveland, Ohio, plant vibration tests a fofally assembled, high-efficiency motor to NEMA standards fo ensure fhaf if meets quality and efficiency s fandards EDWW SWAlV Reliance Electric Industrial Co Cleveland, Ohio M otors today use more than 50% of all electrical energy produced in the US It s no surprise then that advocacy groups and the government have pushed for legislation that mandates highei efficiency in motors aid va;iab!espeed drive systems In fact, a recent study performed by the Department of Energy indicates that by the year 2010, US industry could save 240 billion kw-hr annually by replacing standard-efficiency motors and drives with m:=t~rs thzt xc only 2 to 6% more efficient Today, only about 15% of the motors sold nationwide are energy-efficient One problem is that traditional buying practices don t factor in the real cost of energy For example, buyers responsible for purchasing motors often concentrate on a low purchase price They are largely unaware that higher efficiency motors, although more expensive initially, often more than make up the difference with lower operating costs over the machine s life Another reason for the lack of widespread interest in high-efficiency motors is that few buyers and users understand the relationship between motor efficiency and life-cycle costs Worse, motor manufacturers around the world determine efficiency in different ways, bombarding consumers with confusing and often conflicting marketing data and test results The US government finally stepped in last year to help reduce the confusion and to promote energy conservation It now mandates use of high-efficiency motors for new applications and encourages development of advanced energy-efficient motors and variable speed drives Further, the legislation clears up labeling and performance claims and eliminates old misunderstandi~gs ahst mator efficiency The result is that consumers can run their systems and

2 equipment at high efficiency and know what the costs are I;ettig in the act The vehicle for improving industry-wide efficiency is a comprehensive set of governolent regulations, the Energy Policy Act of 1992 (Epact) The scope of the legislation covers standards for a variety of electrical components, including electric motors, and establishes that the DOE will further prescribe and develop testing and labeling procedures for these regulated products Most large motor makers support the Epact It will level the playing field for all manufacturers, both US and foreign, forcing them to follow the same minimum standards for design, testing, and labeling Furthermore, it ensures users in the US that the energy-efficient motors they pur- chase under any brand name will perform t= specificpbions* Epact dictates that motor manufacturers provide designs typically two to six percent more efficient than current standard motors This improvement comes from reducing motor losses in five areas: winding copper, rotor slip, core, friction and windage, and stray-load loss Motor losses can drop by as much as 50% through use of improved materials, optimized geometry, and better matching the rimtor ST drive system to the husi mzehine And improved manufacturing processes

3 with strict quality control ensure consistently reproduced, high-efficiency motors It s the law The efficiency standards, by law, go into effect on October 24, 1997 They apply to polyphase, integral general-purpose miiiois manufactured or imported for use in the US whether sold separately or as a component in another piece of equipment The standards define nominal full-load efficiencies or the average efficiency of a population of motors of duplicate design These standards are the same as those in the XEMA Stafidards MG- 1, Table 12-K, fgr open and enclosed motors with two, four, 42 MACHlNEDESICNOCTOBER 8,1993

4 2005 and six poles The Department of Energy, Office of Codes and Standards, is respdnsible for clarifying the intent of the Epact, as well as administering and ruling on the motor standards The Epact contains exemptions for definite purpose and special-purpose motors or motors that are determined to be not technically feasible or economically justified These include step motors and servomuiois for exafiiple The initial price premium of an energyefficient motor over a standard motor is typically 15 to 30% Though the efficiency improves only two to six percent, the cost difference can be recovered rapidly because of the larger ratio of the annual operating cost to initial purchase price A comparison of price premium per kilowatt saved illustrates the economies The Epact mandates that for cost-benefit evaluation, the value of energy saved must offset the initial purchase cost premium in less than three years For example, a motor running for three years typicaiiy logs in about 6,000 operating hours Multiplying that by a $008/kW-hr utility rate yields a $480 premium justified for every kw saved To find the savings for a 25 hp motor, calculate the power input for an 883%-efficient motor and compare it to a new 93%-efficient motor The power saved is the difference betureen the two results To calcdata: power, P,, = Ph, x Ef, where P,, = input power, kw; Php = motor, hp; and Ef = motor efficiency For an 883%, 25-hp standard efficiency motor, P,, = 25 x 0746/0883 = 21P2kW9 and for a 93% efficiency motor, P,,, = 25 x 0746/093 = 2005kW Therefore, the power saved = 2112 ~ = 107 kw, and the premium = 107 kw x $480/kW = $513 saved by using the higher &c % *iiciency motor These simple calculations provide the

5 first cut for comparing motors However, users must consider many other factors when evaluating long-term projects Net present value and internal rate of return better indicate the long-term benefits of alternative choices The economic study should also include maintenance cost, demand cost, and expected cost of energy discounted back to the present value in the year of initial installation (Refer to Motors Get a Mandate for Efficiency, MACHINE DE- SIGN, May 14, 1993) Many electric utility companies provide incentives in the form of rebates that can be applied to the purchase of an energy-efficient mctor, This should obviously be in- cluded with any economic analysis The Epact encourages utilities to continue these programs, and the subsidies (rebates) will be partially tax free beginning in 1995

6 I,, ~ ' ~,, F,