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Advances In Construction Techniques Of AC Induction Motors Preparation For Super-Premium Efficiency LevelsAdvances inConstruction Techniquesof AC Induction MotorsPreparation forSuper- PremiumEfficiency LevelsThis material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement ofany of Baldor Electric Company’s products or services. Internal or personal use of this material is permitted. However, permissionto reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale orredistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org. By choosing to view this document, youagree to all provisions of the copyright laws protecting it.Copyright Material IEEEPaper No. PCIC-2004-SF1John MalinowskiIEEE Senior MemberBaldor Electric CompanyPO Box 2400Fort Smith, AR 72902USAJim McCormickIEEE Senior MemberBaldor Electric CompanyPO Box 2400Fort Smith, AR 72902USAAbstract - Design, material and productiontechniques are evolving on AC induction motors leadingto improved efficiencies over older designs. IEEE 841and even NEMA Premium efficiency levels are nowquite easy to meet and exceed. New research andproduction techniques will allow construction of ACmotors with die cast copper rotors allowing even higherefficiency levels and greater longevity.Index Terms: Motor efficiency, Premium efficiency, NEMAPremium , EPAct, IEEE 841, die-cast copper rotor.Kevin DunnIEEE MemberBaldor Electric CompanyPO Box 2400Fort Smith, AR 72902USAI. INTRODUCTIONThe paper will review design and production techniquesrequired for premium efficiency motors and introducenew research being done to further raise efficiency,including better lamination steel slot designs and diecast copper rotors. Development to increase efficiencywith existing practices and materials may be nearingthe end of its cycle.1
Advances In Construction Techniques Of AC Induction Motors Preparation For Super-Premium Efficiency LevelsHistory of premium efficient motors and standardswill be reviewed. The various standards from IEEE,CSA, IEC and JEC will be compared. Segregated motorlosses will be discussed and how they effect efficiency.Using copper rotors can reduce rotor losses andimprove die-casting consistency compared to die castingwith aluminum. Challenges for production include toolingstresses and thermal shock from the higher melting pointof copper versus aluminum.Above-NEMA Premium efficiency levels are possiblewithout the additional cost and complexity of superconducting designs. Motors of all IEEE 841 output ratings(1 HP - up) can be built using these design features toachieve higher efficiencies.II. MOTOR EFFICIENCYA. History of Premium EfficiencyThe high efficiency levels of today’s IEEE 841 motorshave been developed over the last twenty years. Severalmanufacturers introduced “premium” efficient motors inthe early 1980’s. These motors used better laminationmaterial, more active material (laminations and copper)and lower loss cooling fans. But there were no guidelinesas to what efficiency the motor was required to produceto be called a “high efficiency” motor.standard first defined in NEMA MG 1-1998, Rev 2does not differentiate between mounting configurationsand all types of motors are covered.IEEE 841 covers 1 – 500 HP (0.75 – 370 kW)TEFC 2, 4, 6 and 8-pole motors. With adoption of IEEE841-2001, minimum nominal motor efficiency was setat the EPAct level plus 1 NEMA efficiency level. Theprevious 841-1994 was at EPAct levels. Looking at theefficiencies of motors from most manufacturers, theirnominal efficiency complies with NEMA Premium . It isexpected that the NEMA Premium efficiency levels willbe the new minimums for the next revision of IEEE 841.A comparison of 4-pole TEFC efficiencies is shown inTable 1.The European Union (EU) and Committee ofEuropean Manufacturers of Electrical Machines andpower Electronics (CEMEP) have developed a motorefficiency classification scheme for motors in the rangeof 1.1 – 75 kW. These nominal efficiencies are shownin Table 2. Motors sold in Europe will have en efficiencymarking designating Eff1 for their best efficiency, Eff2for standard efficiency. There is a lower Eff3 level for afamily of motors that the EU is encouraging manufacturersto discontinue. Eff1 motor efficiency is comparable tothe U.S. EPAct motor. There are current discussions to setminimum regulated standards as the U.S. has done withEPAct.The National Electrical Manufacturers Association(NEMA) first made a definition between Standardand Energy Efficient motors in MG 1-1987 with theirSeptember 1990 revision. These “Energy Efficient”motor efficiencies later became the standards for theEnergy Policy Act of 1994 (EPAct).In October 1997, the Energy Policy Act of 1994 tookeffect mandating minimum efficiency levels for generalpurpose TEFC and ODP 1 – 200 HP (0.75 – 150 kW)2, 4, 6 and 8-pole foot-mounted motors. This requiredthat any EPAct motor sold in the United States complywith minimum nominal efficiency, testing and labelingstandards. EPAct does not cover “special purpose”motors such as footless motors with C-faces; pumpmountings or other non-standard mountings.The Consortium for Energy Efficiency (CEE) established“premium” efficiency guidelines used by many utilitiesfor rebate programs in 1996. In mid-2001, NEMA andCEE harmonized their efficiency standards, establishingNEMA Premium efficiency standards for ODP and TEFC1 – 500 HP (0.75 – 370 kW) 2, 4 and 6-pole motorsin low and medium voltage. The NEMA Premium 2
Advances In Construction Techniques Of AC Induction Motors Preparation For Super-Premium Efficiency LevelsTABLE 1NOMINAL EFFICIENCY FOR 4-POLE TEFC MOTORSTABLE 2CEMEP MINIMUM NOMINAL EFFICIENCYSTANDARDS FOR 4-POLE MOTORSIEC TEST METHODHPKWEPActIEEE841-2001NEMAPremium 10.7582.584.085.51.51.184.085.586.5HPkWEff 1Eff 221.584.085.586.51.51.183.876.21.585.078.5Motor SizeMotor 340-95.496.2500370-95.496.2Source: European Union – CEMEP 1999Efficiency standards are being developed andadopted throughout the world, mostly by governmentenergy organizations. Some countries adopt theIEEE/CSA methodology and others choose the IECtesting methods. England, Australia, Brazil, Thailand,Singapore and China are among those countries thathave adopted efficiency standards.B. Development of electrical grade lamination steelOver the last 20 years, development and refinementof the motor designs have reduced internal lossesproducing efficiency levels consistent with NEMAPremium . The primary advancement is better electricalgrade steel. Lamination coatings have evolved frombasic organic (C3) to various inorganic / combinationconfigurations (C4/C5/C6) and recently to oxidecoatings. Actual losses in the steel have gone from 4-5watts per pound of steel to less than 2 watts per pound.See the chart in Appendix A showing the reduction iniron loss over the last 20 years.In API 541, C5 inorganic core plate is specified forlow electrical losses and a good resistance to degrading3
Advances In Construction Techniques Of AC Induction Motors Preparation For Super-Premium Efficiency Levelsduring any burnout and rewind process. EASA guidelinesfor burnout temperatures during rewind are 400 C(752 F). Some new proprietary oxide coatings allowtemperature limits of 480 C (896 F) without damage.Damage of lamination steel during an improperlyperformed motor rewind burnout causes increased corelosses. Table 3 illustrates the effect of increased core losson a 50 HP (37 kW) 2-pole ODP motor. If the rewindwas incorrectly performed, it will not take long for theoperating costs of a poorly rewound motor to cost morethan the rewind. Select a service shop that followsANSA/EASA AR100-1998 Recommended Practice forthe Repair of Rotating Electrical Apparatus.TABLE 3EFFECT OF INCREASED CORE LOSS ON MOTOROPERATING COST AND INSULATION LIFE FOR A50 HP 2-POLE ODP MOTORCore LossIncreaseIncrease inAnnualOperating CostTemp.Rise CApprox.Decreasein Insulation Life%%Watts % 3832138200206010841102962Source: Montgomery 1989C. Additional benefits of premium motorsAdditional active material (laminations and copperwire) is added to increase efficiency. IEEE 841 motorsspecify cast iron motor housings that are usually finnedfor increased heat dissipation. Laminations are fullyround on their outer diameter to better provide forincreased thermal conductivity to the motor housing.Smaller internal and external fans are used due to lowerlosses, thus decreasing windage losses.In addition to using better laminations and morecopper, NEMA Premium efficient motor manufacturingtolerances and practices are held to tighter tolerances.Typically vibration levels are lower, generally to halfof NEMA limits or better. NEMA Premium motors areavailable in most enclosures.TEFC motors through 10 HP (7.5 kW) are offeredas either steel band or cast iron housings. Steel bandconstruction is available on ODP motors through 200HP (150 kW) with cast iron on the higher outputratings. Cast iron frames offer greater structural rigidity,increased vibration damping and a flatter mountingbase for easier alignment. When compared to rolledsteel frame motors, the radial finned housing of thesecast iron TEFC motors provides better heat dissipation.D. How Efficiency Is MeasuredThe U.S. standard test for motor efficiency is IEEEStandard 112, Method B. The equivalent CanadianStandards Association (CSA) test is C390-98 and is alsoaccepted by the U.S. Department of Energy. The IEC teststandard is 60034-2. This is not an equivalent test toIEEE 112 because IEC 60034-2 and the proposed IEC61972 tests assign specific values to stray load lossesrather than measuring the losses as in IEEE tests. Table 4shows the IEC assigned losses.TABLE 4IEC DEFAULT VALUES FOR STRAY LOAD LOSSESMotor SizeAssumed stray load losses(% of full-load input power)HPkWIEC 60034-2IEC 70.501.602682000.501.504
Advances In Construction Techniques Of AC Induction Motors Preparation For Super-Premium Efficiency LevelsWhile the IEC procedure assigns stray load losses,the JEC-37 efficiency test standard for Japan ignoresstray load losses altogether. Only IEEE 112 and CSAC390-98 tests actually compare measured input andoutput watts giving a true measurement of the motor’sactual efficiency. Test results using IEC and JEC methodscannot be directly compared with IEEE 112 or CSAC390-98 because they do not contain a measurementof all of the motor’s losses. A comparison of efficiencyof a single motor when testing by each method is shownin Table 5.IEEE and CSA methods accurately measures wattsin and watts out that allow for segregating the motor’slosses into five categories:Iron Core Losses – Magnetic losses in laminations,inductance and eddy current losses.Stator Resistance – Current losses in the windingsRotor Resistance – Current Losses in the rotor barsand end ringsWindage and Friction – Mechanical drag in bearingsand cooling fansStray Load losses – Magnetic transfer loss in the airgap between the stator and rotorTABLE 5APPROX. ESTIMATION OF COMPARABLE EFFICIENCYLEVELS USING JEC, IEC AND IEEE TEST METHODSMotor SizeMotor EfficiencyHPkWIEEE112B/C390-98IEC 94.394.6The charts in Appendix B illustrate segregated lossesbased on C390-98 tests in various motors designs.While some losses remain consistent, others are reduced,resulting in improved overall efficiency of the machine.Motor designers debate on how these losses should bedistributed for a motor’s performance characteristics,but the total of the losses is most important to efficiency.For example, certain losses might be further reduced,but this could result in a motor that would not be capableof starting across the line. Such a motor might be wellsuited for use with an adjustable speed drive or softstart that limits inrush current but the motor would havedifficulty starting across the line with a control bypass.General-purpose motors often have design compromisesas a result of the designer’s effort to balance performanceparameters.E. Additional efficiency-gaining considerationsReduced motor losses allow use of a smaller coolingfan with less friction and windage. Bearing sizes couldbe reduced for greater efficiency, but shaft loadingwould be limited especially with belted loads.For maintenance reasons, some users prefer the useof the same size bearing on both ends of the motor.Addition of a larger bearing on the opposite drive end(making it the same as the drive end) increases frictionand reduces motor efficiency. The opposite drive endbearing is lightly loaded and doesn’t require this largebearing for typical loads. Reviewing IEEE 841 motorsproduced by various manufacturers, about half use thesame bearings on each end and the other half use asmaller bearing on the fan-end than the drive end. Table6 illustrates the additional power losses when using twobearings of the same size compared to use of a smallerbearing on the opposite drive end for NEMA 250 – 360frame motors.Using hybrid bearings that have ceramic balls insteadof steel balls may further reduce bearing losses. Testshave shown that these bearings also run cooler andprovide longer life than conventional deep-groove ballbearings. The ceramic balls would have the additionalfeature of isolating the shaft and preventing bearingfluting from circulating currents caused by ASDs.Source ERM 19995
Advances In Construction Techniques Of AC Induction Motors Preparation For Super-Premium Efficiency LevelsTABLE 6COMPARISON OF SAME-SIZE BEARINGON BOTH ENDS OF IEEE 841 MOTORS TOCONVENTINAL CONSTRUCTION WITHTWO DIFFERENT SIZE BEARINGS%Increasein creasein .17.936511609.19.27.9IEEE 841 specifies a Polyurea-based grease to beused in motors. Many users specify lithium-based orsynthetic greases. Non-petroleum greases may offerlower losses, operation at higher temperatures andlonger life between lubrication. The IEEE 841 committeewill be reviewing grease considerations for the nextrevision.According to EASA figures, about 60% of prematuremotor failures involve the motor bearing system. MostIEEE 841 motors utilize a non-contact labyrinth sealto minimize contamination of the bearings. Somemanufacturers supply these seals on both the drive andfan-end of the motor. Contact seals cause friction lossesand their sealing capabilities are reduced as wear takesplace.Bearing manufacturers are also working on noncontact and lower friction bearing seals for applicationswhere sealed bearings are required. Ceramic balls inanti-friction bearings may offer lower losses, reducedlubrication intervals and a “self-healing” feature ifcontamination is introduced into the bearing.F. Future DevelopmentsSeveral technical improvements promise to produceAC induction motors with efficiency levels exceedingNEMA Premium . High temperature super-conductingshows promise on higher-powered motors. Developmentof better lamination steel, such as EMTX (Enhancedmagnetic textures that fundamentally change themagnetic characteristics of steel), also shows promise.Amorphous materials may become a factor in futuremotor design but their costs are still prohibitive, materialis difficult to obtain and manufacture. Copper rotors area proven technology, accepted on higher horsepowermotors, but not available as general-purpose productsfor motors less than 250 HP (190 kW).III. USE OF COPPER ROTORS1 – 500 HP (.75 – 373 kW) TEFC motors used inthe petroleum and chemical industry are often built incompliance with IEEE Standard 841-2001, which doesnot specify copper rotors. Most of these motors havedie cast aluminum rotors. Use of copper bar rotors iscommon on above-NEMA sized motors, 250 HP (190kW) and larger. API (American Petroleum Institute)Standard 541 specifies that AC induction motors shouldutilize copper bar rotors.Copper bar rotors are exactly that, extruded copperbars, fabricated in the rotor by brazing to copper endrings. Reasons for copper rotors are lower rotor currentlosses producing higher motor efficiency and betteroverall performance. Copper has better conductivitythan aluminum by nearly 60%, therefore the crosssection of the rotor bar for copper motors is smallerthan that of an aluminum rotor motor. Less volume ofcopper is required, somewhat offsetting its higher costper pound.IV. DEVELOPMENT OF NEW CASTINGDIE MATERIALHigh-pressure die casting of aluminum squirrel-cagerotors is a mature process performed by most motormanufacturers on motors through 2000 HP (1500 kW).The melting point for aluminum alloys is in the 676 C(1250 F) range. The material used for the rotor’s diecasting mold is often H-13 tool steel, which is not highlystressed at these temperatures. Die life can be in thehundreds of thousands of rotors depending on diecomplexity. Copper melts at 1083 C (1982 F). This highmelting temperature results in failure of conventional diesteels by thermal fatigue of the surface (“heat checking”)in less than 100 shots.Recent development work has demonstrated that hightemperature nickel-base alloy dies (e.g. INCONEL alloy617) will markedly increase die life when die-castingcopper. Although not tested in this work, HAYNES alloy6
Advances In Construction Techniques Of AC Induction Motors Preparation For Super-Premium Efficiency Levels230 has similar properties and is conventionally weldrepairable. Production experience will determine actualuseful die life in production of copper rotors using the new,elevated temperature nickel-base alloy die technology. Toreduce thermal stressing, the die is pre-heated to 600650 C (1112-1202 F) before casting the copper.V. COPPER ROTOR RESEARCHA. Initial copper rotor researchDuring development, a 15 HP (11 kW) 4-poleTotally enclosed fan-cooled (TEFC) motor design waschosen because the rotor size fit the capabilities of thedie casting press at the research facility. During thefirst phase, rotor laminations that were designed foraluminum rotors were used to prove the copper castingprocess. One motor stator and set of endplates wereused to test the consistency of the rotor performance.Rotors were cast in a 750-ton (650-metric ton)horizontal die-casting machine. Chopped copper wirerod was used for the casting material. The copper wasmelted as required for each shot in an induction furnaceto control the problems of oxygen and hydrogen in themolten copper over time. With only a 60 kW supply,the furnace required about 13 minutes for the melt to1230 C (2246 F), providing about 150 C (302 F) ofsuperheat.A heated shot sleeve surrounded with a thermalwrap was used. The shot sleeve was sized for the rotorrequirements to minimize air entrapment and porosity inthe casting. After casting, the rotor was water quenchedbecause it was believed that the rapid cooling wouldbreak the copper away from the laminations a
accepted by the U.S. Department of Energy. The IEC test standard is 60034-2. This is not an equivalent test to IEEE 112 because IEC 60034-2 and the proposed IEC 61972 tests assign specific values to stray load losses rather than measuring the losses as in IEEE tests. Table 4 shows the IEC assigned losses. TABLE 3 EFFECT OF INCREASED CORE LOSS .
Image restoration techniques are used to make the corrupted image as similar as that of the original image. Figure.3 shows classification of restoration techniques. Basically, restoration techniques are classified into blind restoration techniques and non-blind restoration techniques [15]. Non-blind restoration techniques
construction techniques grows, it is expected that some of these theories will prove to be transferable to the homcbuilder\ list of radon-resistant construction options. The soil ventila-tion techniques described HAVE been extensively tested in existing homes and show good potential for application m new construction and are, therefore .
TECHNOLOGY IN CONSTRUCTION . There are many reasons why time and technology is important in construction. so time management will help control salary costs and construction cost. Another reason for time management in construction is to carry and finish the work as per the schedule, Time management in construction also is vital
The construction industry experiences a larger burden of deaths at road construction sites than any other major industry. From 2011 to 2016, 532 construction workers were killed at road construction sites, more than twice as many fatalities as all other industries combined (chart 3). The number of fatalities among construction workers at
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techniques were described in chapter 4. It's important to combine two or more diversity techniques to get full advantage of diversity techniques. Some diversity combining techniques were described in chapter 5. The mathematical equations needed for simulation in diversity combining techniques were collected and defined in chapter 6.
2.1 A Review of Credit Scoring Techniques . Credit Scoring techniques are divided into two parts . i. Statistical Based Techniques ii. Artificial Intelligence Based Techniques . 2.1.1 Statistical Based Techniques . Various credit scoring statistical based techniques have been researched on and implemented. These statistical based tech-
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