1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA MG 10-2017Energy Management Guide for Selection and Use of Fixed FrequencyMedium AC Squirrel-Cage Polyphase Induction MotorsNEMA MG 10-2017 Energy Management Guide for Selection and Use of Fixed Frequency Medium AC Squirrel-
2、Cage Polyphase Induction Motors Published by National Electrical Manufacturers Association 1300 North 17thStreet, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2017 National Electrical Manufacturers Association. All rights, including translation into other languages, reserved under the Universal Co
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5、ch the document contained herein is one, are developed through a voluntary consensus standards development process. This process brings together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. While NEMA administers the process and esta
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13、nt. NEMA MG 10-2017 Page i 2017 National Electrical Manufacturers Association CONTENTS Foreword . ii Scope ii Section 1 Introduction 1 1.1 Referenced Standards . 1 1.2 General 2 1.2.1 Medium Motors . 2 1.2.2 Usual Service Conditions 2 1.3 Power Supply. 3 1.3.1 Ratings 3 1.3.2 Effects of Variation in
14、 Voltage and Frequency 3 1.3.3 Effects of Voltage Unbalance 3 1.4 Efficiency . 3 1.4.1 Motor Losses . 7 1.4.2 Variations in Motor Losses 7 1.4.3 Efficiency Testing Methods . 8 1.4.4 Testing Variations . 8 1.4.5 Manufacturing Variations 8 1.4.6 NEMA Standards on Efficiency Nomenclature and Labeling 8
15、 1.5 Evaluation of Efficiency Economics . 13 1.5.1 Simple Payback Analysis 13 1.5.2 Present Worth Life Cycle Analysis 14 1.6 Motor Selection 15 1.6.1 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.
16、2 Applications Involving Extended Periods of Light Load Operation . 21 1.8.3 Applications Involving Throttling or Bypass Control 21 1.8.4 Applications Involving Overhauling Loads 23 Section 2 Maintenance . 24 NEMA MG 10-2017 Page ii 2017 National Electrical Manufacturers Association Foreword The Mot
17、or 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 to date with evolving technology. MG 10-2013 is the result of this commitment to include typical characteristics of IEC Design H and N induction
18、motors and information on the NEMA energy efficient and Premium efficiency motor standards. The goal of this guide is to assist the reader in the choice of equipment for his application. The practice of periodically reviewing and updating the guide will be continued. Comments from readers are welcom
19、ed and should be addressed to: Senior Technical Director, Operations National Electrical Manufacturers Association 1300 North 17thStreet, Suite 900 Rosslyn, Virginia 22209 Scope This energy management guide provides practical information concerning the proper selection and application of medium AC p
20、olyphase squirrel-cage induction motors, including installation, operation, and maintenance in fixed frequency applications. NEMA MG 10-2017 Page 1 2017 National Electrical Manufacturers Association Section 1 Introduction The shortage and large cost increases of vital national energy resources has d
21、emonstrated the need to conserve such resources. In 1992 the Energy Policy Act mandated minimum levels of nominal efficiency that some classes of motors were required to meet after October 27, 1997. As a result of market demand for standardization in the identification of motors having efficiency th
22、at exceeded the levels set by the Energy Policy Act, NEMA introduced the new Premium efficiency motor standard in June 2001. In 2007 the U.S. Congress passed the Energy Independence and Security Act (EISA), increasing the level of the efficiency standards on existing covered electric motors and addi
23、ng efficiency standards for additional types of electric motors manufactured on or after December 19, 2010. In February 2011 NEMA revised Premium efficiency motor tables for medium motors by adding efficiency values for 8-pole Premium efficiency motors. It is important that motor users and specifier
24、s understand the selection, application, and maintenance of electric motors in order to improve the management of electrical energy consumption. Energy management as related to electric motors is the consideration of factors that contribute to reducing the energy consumption of a total electric moto
25、rdriven system. Among the factors to be considered are the motor design and application. An electric motor is an energy converter, 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, wi
26、th specific operating characteristics that dictate the starting and running load characteristics of the motor. Consequently, 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 accelera
27、tion, speed, load, duty cycle), service conditions, motor efficiency, motor power factor, and initial motor cost. These application 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
28、motor, these components include the driven equipment (such as fans, pumps, and compressors) and power transmission components (such as belts, pulleys, gears and clutches). Other components that are not a part of the driven system will affect the overall system efficiency. Some of these are refrigera
29、tor and air conditioning evaporator and condenser coils; piping associated with pumps, ducts and baffles associated with fans and blowers; and motor controllers (ac variable speed drives and power factor controller). Good energy management is the successful application of the motor controller, motor
30、, and the driven components that results in the least consumption of energy. Since all motors do not have the same efficiency, careful consideration must be given to their selection and application. 1.1 Referenced Standards Canadian Standards Association 178 Rexdale Boulevard Toronto, Ontario, Canad
31、a M9W 1R3 CSA C390-10 (R2015) Test methods, marking requirements, and energy efficiency levels for three-phase induction motors NEMA MG 10-2017 Page 2 2017 National Electrical Manufacturers Association Institute of Electrical and Electronics Engineers (IEEE)1445 and 501 Hoes Lane Piscataway, NJ 0885
32、4-4141 IEEE Std 112-2011 Standard Test Procedure for Polyphase Induction Motors and Generators National Electrical Manufacturers Association 1300 North 17thStreet, 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 Mot
33、ors and Generators defines a medium machine as a machine: (1) built in three- or four-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 12013600 50
34、0 9011200 350 721900 250 601720 200 515600 150 451514 125 1.2.2 Usual Service 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
35、 steps in selecting a motor consist of determining the power supply, horsepower 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 als
36、o be properly selected with respect to the known service conditions, often referred 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) Ex
37、posure to an altitude that does not exceed 3300 ft. (1000 m). c) Installation in areas or supplementary enclosures that do not seriously interfere with the ventilation of the machine. d) Operation within a tolerance of 10%of rated voltage. e) Operation from a sine wave of voltage source (not to exce
38、ed 10%deviation factor). f) Operation within a tolerance of 5%of rated frequency. g) Operation within a voltage unbalance of 1% or less. 1Also available from ANSI. NEMA MG 10-2017 Page 3 2017 National Electrical Manufacturers Association Operation at other than usual service conditions may result in
39、 the consumption of additional energy. 1.3 Power Supply 1.3.1 Ratings In general, induction motors are designed for a rated voltage, frequency, and number of phases. The supply voltage must be known in order to select the proper motor. For ac motors, the motor rated voltage will normally be equal to
40、 the utilization voltage, which is less than the nominal power system voltage as shown in the following table for three-phase, 60 Hz motors. Nominal Power System Voltage, V Utilization Voltage, V 120 115 208 200 240 230 480 460 600 575 2400 2300 4160 4000 6900 6600 In situations where the available
41、voltage is equal to the system voltage, the motor rated voltage should be chosen appropriately. 1.3.2 Effects of Variation 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 performa
42、nce characteristics. The same condition is true when operating the motor on other than a sine wave of voltage. The effect 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 Volta
43、ge Unbalance A balanced voltage of the three-phase power supply to the motor is essential to the efficient operation of the system. For example, a voltage unbalance of 3.5%can increase motor losses by approximately 20%. For this reason, single-phase loads taken from a three-phase power supply should
44、 be carefully allocated so that the voltage unbalance will be kept as low as possible at the motor terminals. 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
45、: Losses Output+Output= InputOutput= Efficiency Motor efficiencies are usually given for rated load, load and 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 characterist
46、ic of motors (see Figure 1). Operation of the motor at loads substantially different from rated load may result in a change in motor efficiency. NEMA MG 10-2017 Page 4 2017 National Electrical Manufacturers Association b) Generally, the full-load efficiency of motors increases as the motor horsepowe
47、r rating increases (see Figure 1). c) For the same horsepower rating, motors with higher speeds generally, but not necessarily, have a higher 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 sp
48、eed-changing mechanisms, such as pulleys or gears, are required to obtain 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. Figure 1 Typical Efficiency Versus Load Curves for 1800
49、RPM Three-Phase 60 HZ 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 less 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 full-load speed. Slip, expressed in percent, is the difference in speeds divided by the synchronous speed and multiplied by 100. Therefore, under steady load conditions, NEMA Design A, B, and C, and IEC Design H and N squirrel-cage
