Motors efficiency

High sihcon steels (historically 3.75—5.00% but more recentiy 6% Si) are used in power transformers and high efficiency motors, generators, and transformers, and in communications equipment. 

Further incentives to use energy-efficient motors are provided by various cost rebate programs offered by utilities based on norsepower rating and efficiency level. Another factor that will have a significant impact is the Energy Policy Act of 1992, in which the U.S. Congress established limits on the lowest level of nominal efficiency that certain classes of motors of standard design can have after 1997. 

Table 1 from the GPSA Engineering Data Book compares standard and high efficiency motors. Table 2 from GPSA compares synchronous and induction motors. Table 3 from Evans shows the effect of a large range of speeds on efficiency. 

Variable-speed fan drives permit conditioned air distribution to be matched more closely to a building s needs. High-efficiency electric motors are used to drive the fans, saving as much as half the energy once used. Both variable-speed and high- efficiency motors are being applied even in residential air conditioning systems. 

Refrigerators declined in efficiency following World War II due, apparently, to the substitution of lower-cost, lower-efficiency motors with improved thermal insulation to protect them from waste heat generation, and there is some evidence that water heater efficiency declined between the end of World War II and 1975, and that industrial dry-type transformers declined in efficiency between 1970 and 1993. 

Even when the time comes to make a purchasing decision, an energy-efficient motor purchase is not a certainty. Sometimes an energy-efficient motor will be the economically efficient choice at other times, not. The capital investment decision is based on the cost in relation to performance, efficiency and reliability. Moreover, the decision depends on the application and the amount of time the motor is in operation. It can be the major component of a product (drill or mixer), or a minor component (computer disk drive) it can be the major component cost of a product (fan), or it can be a minor component cost (stereo tape deck) it can run almost constantly (fan, pump, and machinery), or only a few minutes a day (vacuums and power tools). For example, contractors purchase circular saws almost solely based on performance and reliability. Time is money, and since the saw is operating only a few minutes a day and the contractor is often not responsible for the electricity costs to run the motor, energy efficiency is not a consideration performance and reliability are what matter most. On the other hand, an industrial user, who runs huge electric motors twenty-four hours a day to work pumps, machinery, and ventilation equipment, is very concerned tvitli energy efficiency as well as performance and reliability. 

Almeida, A. (1992). Energy-Efficient Motor Systems A Handbook on Technologies, Programs and Policy Opportunities. Washington, UC American Council for an Energy Efficient Economy. 

Full-Load Efficiencies of Energy-Efficient Motors... 

Montgomery, D. C., Evaluation of Energy Efficient Motors, pr sented to Textile Industry Electrical Conference, MO, (1979). The Institute of Electrical and Electronics Engineers, Inc., NY... 

Parke, H. G., Can Energy Efficient Motors Save You Money , Energy Management Technology, p. 42, May/June... 

Kohn, P. M., Energy-Efficient Motors Gain Wider Interest, Chem. Eng, V. 86, p. 49,July 16, (1979). 

Chapter 14, Mechanical Drivers, has been updated to inlcude the latest code and standards of the National Electrical Manufacturer s Association and information on the new energy efficient motors. 

You need a pump that will develop at least 40psi at a flow rate of 300 gpm of water. What combination of pump size, motor speed, and impeller diameter from the pump characteristics in Appendix H would be the best for this application State your reasons for the choice you make. What are the pump efficiency, motor horsepower and torque requirement, and NPSH for the pump you choose at these operating conditions ... 

Hirzel, J. Understanding premium-efficiency motor economics. Plant Eng. 1992, 7, 75-78. 

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