NEMA MG 10-2013 Energy Management Guide for Selection and Use of Fixed Frequency Medium AC Squirrel-Cage Polyphase Induction Motors.pdf

1、 NEMA MG 10-2013 Energy Management Guide for Selection and Use of Fixed Frequency Medium AC Squirrel-Cage Polyphase Induction Motors NEMA MG 10-2013 Energy Management Guide For Selection and Use of Fixed Frequency Medium AC Squirrel-Cage Polyphase Induction Motors Published by National Electrical Ma

2、nufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2014 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Lit

3、erary and Artistic Works, and the International and Pan American copyright conventions. NOTICE AND DISCLAIMER The information in this publication was considered technically sound by a consensus among persons engaged in its development at the time it was approved. Consensus does not necessarily mean

4、there was unanimous agreement among every person participating in the development process. The National Electrical Manufacturers Association (NEMA) standards and guideline publications, of which the document herein is one, are developed through a voluntary standards development process. This process

5、 brings together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. Although NEMA administers the process and establishes rules to promote fairness in the development of consensus, it does not write the documents, nor does it independently

6、 test, evaluate, or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guideline publications. NEMA disclaims liability for any personal injury, property, or other damages of any nature, whether special, indirect, consequential, or

7、 compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on this document. NEMA disclaims and makes no guaranty or warranty, express or implied, as to the accuracy or completeness of any information published herein, and disclaims and makes no warranty t

8、hat the information in this document will fulfill any particular purpose(s) or need(s). NEMA does not undertake to guarantee the performance of any individual manufacturers or sellers products or services by virtue of this standard or guide. In publishing and making this document available, NEMA is

9、not undertaking to render professional or other services for or on behalf of any person or entity, nor is NEMA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advi

10、ce of a competent professional in determining the exercise of reasonable care in any given circumstance. Information and other standards on the topic covered by this publication may be available from other sources, which the user may wish to consult for additional views or information not covered by

11、 this publication. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test, or inspect products, designs, or installations for safety or health purposes. Any certification or other statement of compliance with any healt

12、h- or safety-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. MG 10-2013 Page i 2014 National Electrical Manufacturers Association CONTENTS Foreword . ii Scope ii Section 1 INTRODUCTION . 1 1.1 Referen

13、ced Standards . 1 1.2 General 3 1.2.1 Medium Motors 3 1.2.2 Usual Service Conditions 3 1.3 Power Supply. 3 1.3.1 Ratings 3 1.3.2 Effects of Variation in Voltage and Frequency 4 1.3.3 Effects of Voltage Unbalance 4 1.4 Efficiency . 4 1.4.1 Motor Losses . 8 1.4.2 Variations in Motor Losses 8 1.4.3 Eff

14、iciency Testing Methods . 9 1.4.4 Testing Variations . 9 1.4.5 Manufacturing Variations 9 1.4.6 NEMA Standards on Efficiency Nomenclature and Labeling 9 1.5 Evaluation of Efficiency Economics . 13 1.5.1 Simple Payback Analysis 13 1.5.2 Present Worth Life Cycle Analysis 13 1.6 Motor Selection 15 1.6.

15、1 Induction Motors 15 1.6.2 Multispeed Motors . 15 1.7 Power Factor . 16 1.8 Application Analysis . 18 1.8.1 Applications Involving Load Cycling 18 1.8.2 Applications Involving Extended Periods of Light Load Operation . 21 1.8.3 Applications Involving Throttling or Bypass Control 21 1.8.4 Applicatio

16、ns Involving Overhauling Loads 23 Section 2 MAINTENANCE 24 MG 10-2013 Page ii 2014 National Electrical Manufacturers Association Foreword The Motor and Generator Section of NEMA published the first edition of MG 10 with the statement to periodically review the guide for the purpose of keeping it up

17、to date with advancing technology. This edition, MG 10-2013 is the result of this commitment to include typical characteristics of IEC Design H and N induction motors and information on the NEMA energy efficient and Premium efficiency motor standards. The goal of this guide is to assist the reader i

18、n the choice of equipment for his application. The practice of periodically reviewing and updating the guide will be continued. Comments on the guide from readers are welcomed and should be addressed to: Senior Technical Director, Operations National Electrical Manufacturers Association 1300 North 1

19、7th Street, Suite 900 Rosslyn, Virginia 22209 Scope This energy management guide provides practical information concerning the proper selection and application of medium AC polyphase squirrel-cage induction motors including installation, operation, and maintenance in fixed frequency applications MG

20、10-2013 Page 1 2014 National Electrical Manufacturers Association Section 1 INTRODUCTION The shortage and large cost increases of vital national energy resources has demonstrated the need to conserve such resources. In 1992 the Energy Policy Act mandated minimum levels of nominal efficiency which so

21、me classes of motors were required to meet after October 27, 1997. As a result of the market demand for standardization in the identification of motors having efficiency that exceeded the levels set by the Energy Policy Act, NEMA introduced the new Premium efficiency motor standard in June of 2001.

22、In 2007 the U.S. Congress passed the Energy Independence and Security Act increasing the level of the efficiency standards on existing covered electric motors and added efficiency standards for additional types of electric motors manufactured on or after December 19, 2010. In February of 2011 NEMA r

23、evised Premium Efficiency Motor tables for medium motors by adding efficiency values for 8 pole Premium efficiency motors. It is important that motor users and specifiers understand the selection, application, and maintenance of electric motors in order to improve the management of electrical energy

24、 consumption. Energy Management as related to electric motors is the consideration of the factors that contribute to reducing the energy consumption of a total electric motor-driven system. Among the factors to be considered are the motor design and application. An electric motor is an energy conver

25、ter, converting electrical energy to mechanical energy. For this reason, an electric motor should be considered as always being connected to a driven machine or apparatus, with specific operating characteristics, which dictate the starting and running load characteristics of the motor. Consequently,

26、 the selection of the motor most suitable for a particular application is based on many factors, including the requirements of the driven equipment (e.g., starting and acceleration, speed, load, duty cycle), service conditions, motor efficiency, motor power factor, and initial motor cost. These appl

27、ication factors often conflict with one another. The driven system efficiency is the combination of the efficiencies of all of the components in the system. In addition to the motor, these components include the driven equipment (such as fans, pumps, and compressors) power transmission components (s

28、uch as belts, pulleys, gears and clutches). Other components which are not a part of the driven system will affect the overall system efficiency; some of these are refrigerator and air conditioning evaporator and condenser coils, piping associated with pumps, ducts and baffles associated with fans a

29、nd blowers, and motor controllers (ac variable speed drives and power factor controller). Good energy management is the successful application of the motor controller, motor, and the driven components that results in the least consumption of energy. Since all motors do not have the same efficiency,

30、careful consideration must be given to their selection and application. 1.1 REFERENCED STANDARDS Canadian Standards Association 178 Rexdale Boulevard Toronto, Ontario, Canada M9W 1R3 CSA 390-10 Energy Efficiency Test Methods for Three-Phase Induction Motors Institute of Electrical and Electronics En

31、gineers (IEEE)1 1 Also available from ANSI. MG 10-2013 Page 2 2014 National Electrical Manufacturers Association 445 Hoes Lane Piscataway, NJ 08855-1331 IEEE Std 112-2011 Standard Test Procedure for Polyphase Induction Motors and Generators MG 10-2013 Page 3 2014 National Electrical Manufacturers As

32、sociation National Electrical Manufacturers Association 1300 North 17th Street, Suite 900 Rosslyn, VA 22209 NEMA MG 1-2011 Motors and Generators 1.2 GENERAL 1.2.1 Medium Motors The standards publication, NEMA MG 1 Motors and Generators, defines a medium machine as a machine: (1) built in three- or f

33、our-digit frame number series in accordance with MG 1-4.2.1 (or equivalent for machines without feet); and (2) having a continuous rating up to and including the following: Synchronous Speed, RPM Horsepower 1201-3600 500 901-1200 350 721-900 250 601-720 200 515-60 150 451-514 125 1.2.2 Usual Service

34、 Conditions The proper selection and application of fixed frequency medium AC squirrel-cage polyphase induction motors involves the consideration of many factors affecting installation, operation, and maintenance. The basic steps in selecting a motor consist of determining the power supply, horsepow

35、er rating, speed, duty cycle, motor type, and enclosure. In addition, environmental conditions, mounting, connections of the motor to the load, and mechanical accessories or modifications must be considered. Motors must also be properly selected with respect to the known service conditions, often re

36、ferred to as usual and unusual, as defined in NEMA Standards Publication MG 1, Motors and Generators. Usual service conditions are considered to be: a) Exposure to an ambient temperature within the range of -15C to 40C. b) Exposure to an altitude that does not exceed 3300 feet (1000 meters). c) Inst

37、allation in areas or supplementary enclosures that do not seriously interfere with the ventilation of the machine. d) Operation within a tolerance of 10 percent of rated voltage. e) Operation from a sine wave of voltage source (not to exceed 10 percent deviation factor). f) Operation within a tolera

38、nce of 5 percent of rated frequency. g) Operation within a voltage unbalance of 1 percent or less. Operation at other than usual service conditions may result in the consumption of additional energy. 1.3 POWER SUPPLY 1.3.1 Ratings In general, induction motors are designed for a rated voltage, freque

39、ncy, and number of phases. The supply voltage must be known in order to select the proper motor. For alternating-current motors, the motor rated voltage will normally be equal to the utilization voltage, which is less than the nominal power MG 10-2013 Page 4 2014 National Electrical Manufacturers As

40、sociation system voltage as shown in the following table for three-phase, 60-hertz motors: For alternating-current motors, the motor rated voltage will normally be equal to the utilization voltage, which is less than the nominal power system voltage as shown in the following table for three-phase, 6

41、0-hertz motors. Nominal Power System Voltage, Volts Utilization Voltage, Volts 120 115 208 200 240 230 480 460 600 575 2400 2300 4160 4000 6900 6600 In situations where the available voltage is equal to the system voltage, the motor rated voltage should be chosen appropriately. 1.3.2 Effects of Vari

42、ation in Voltage and Frequency Operation outside of the rated conditions of voltage and frequency may decrease both efficiency and power factor and may adversely affect other performance characteristics. The same condition is true when operating the motor on other than a sine wave of voltage. The ef

43、fect of a variation in supply voltage, wave form, or frequency on the motors efficiency and power factor characteristics depends on the individual motor design. 1.3.3 Effects of Voltage Unbalance A balanced voltage of the three-phase power supply to the motor is essential to the efficient operation

44、of the system. For example, a voltage unbalance of 3.5 percent can increase motor losses by approximately 20 percent. For this reason, single-phase loads taken from a three-phase power supply should be carefully allocated so that the voltage unbalance will be kept as low as possible at the motor ter

45、minals. 1.4 EFFICIENCY Motor efficiency is a measure of the effectiveness with which electrical energy is converted to mechanical energy, and is expressed as the ratio of power output to power input: L o s s e s Ou t p u t +Ou t p u t = In p u tOu t p u t = E f f i c i e n c y Motor efficiencies are

46、 usually given for rated load, 3/4 load and 1/2 load. The efficiency of a motor is primarily a function of load, horsepower rating, and speed, as indicated below: a) A change in efficiency as a function of load is an inherent characteristic of motors, see Figure 1. Operation of the motor at loads su

47、bstantially different from rated load may result in a change in motor efficiency. b) Generally, the full load efficiency of motors increases as the motor horsepower rating increases, see Figure 1. c) For the same horsepower rating, motors with higher speeds generally, but not necessarily, have a hig

48、her efficiency at rated load than motors with lower rated speeds. This does not imply, however, that all apparatus should be driven by high-speed motors. Where speed-changing mechanisms, such as pulleys MG 10-2013 Page 5 2014 National Electrical Manufacturers Association or gears, are required to ob

49、tain the necessary lower speed, the additional power losses could reduce the efficiency of the system to a value lower than that provided by a direct-drive lower-speed motor. d) Figure 1 TYPICAL EFFICIENCY VERSUS LOAD CURVES FOR 1800-RPM THREE-PHASE 60-HERTZ DESIGN B SQUIRREL-CAGE INDUCTION MOTORS A definite relationship exists between the slip and the efficiency of a polyphase induction motor, i.e. the higher the slip, the lower is the efficiency for slip is a measure of the losses in the rotor. Slip of an induction motor is the difference between synchronous speed and