Electrical machines efficiency

Method tor determining losses and efficiency of rotating electrical machines... 

Another aspiect of the Energy Star pirogram is that efficient copy machines not only have the potential to lower direct use of electricity, they also should... 

This may be why cells use electric signals because these are in principle highly efficient. Electrochemical machines (i.e., storage batteries) are just the type that enable large concentration gradients to be balanced by electrical potential jumps so as to preserve the continuity of the electrochemical potential, which is the requirement for reversibility. The concentration gradients of K+ and Na across cell membranes that... 

Most rotating electrical machines above about 500 kW have efficiencies above 95%, which increases to about 98% for large machines in the hundreds of megawatts range. Their losses are dne to windage between the rotor and the stator, friction in the bearings and seals, iron and copper electrical losses. 

Typical applications for electrical steel are in large distribution and power transformers, large generators and high-efficiency rotating machines. To reduce eddy-current loss, electrical steels are laminated into sheets which are usually 0.27-0.64 mm thick. 

It could be noted that the best solution both from an environmental and economic perspective is the installation of high-efficiency electric motors for spinning machines, also related to the most critical process. The second best solution, economically and environmentally, is the substitution of the neon lighting system with the LED technology (Figure 8.6). With the implementafion of these two options it is possible to save 35,403 kg of CO2 equivalent (3% of the emission deriving from the consumption of electric energy). 

Table 8.13 Technical parameters and costs of high-efficiency electric motors for spinning machines...

An electrical machine may be used as a motor or a generator, although in practice the machine will work more efficiently when operated in the mode for which it was designed. 

Electric machines yield a much higher efficiency spreading over a wider area (Figure 35.6). It can exceed 90%, with a less pronounced drop towards part-load operation compared with internal combustion engines. 

Ceramic electromagnets are used in medical magnetic resonance imaging (MRI) machines and in high-efficiency electric motors and generators. 

Variable Flow Rate Conventional variable clearance volume and valve lifting devices are impracticable at high pressures and, should it be necessary to vary the flow rate, use has to be made of variable speed electric drives or magnetic clutches. Integral steam and gas engines have been used and Burckhardt (168) developed an hydrauhc drive to provide an integrated variable capacity machine, but its efficiency is less than that of a straight mechanical drive. 

At least two manufacturers have developed and installed machines rated to produce more than 210 MW of electricity in the simple-cycle mode. In both cases, the machines were designed and manufactured through cooperative ventures between two or more international gas turbine developers. One 50-Hz unit, first installed as a peaking power faciUty in France, is rated for a gross output of 212 MW and a net simple-cycle efficiency of 34.2% for natural-gas firing. When integrated into an enhanced three-pressure, combined-cycle with reheat, net plant efficiencies in excess of 54% reportedly can be achieved. 

Electrostatic-Separation Machines The first electrostatic machines to be used commercially employed the principle of contact elec trification. These were free-fall devices incorporating large vertical plates between which an electrostatic field was maintained. Tribo-elec tric separation (contact charging) has experienced an increase in apphcations due to advances in mechanical self-cleaning and electrical design as well as the development of efficient precharging techniques. 

The North American electric power transmission system has been described as the largest, most complex machine ever built by humanity. It is a massive network of generating stations, transmission lines, substations, distribution lines, motors, and other electrical loads all interdependently linked for the conversion, transportation, and control of electrical energy. Approximately 60 percent of all energy utilized in the United States passes through the interconnected electric power system. The major goal of the system is to most efficiently and reliably deliver electric power from generating stations to residential, commercial, and industrial consumers. 

Natural gas also has an efficiency advantage in electricity generation. The economic and operational superiority of gas-fired combustion turbines and combined-cycle machines (and prospectively, the superiority of gas-powered fuel cells) relative to coal-and nuclear-powered steam turbines made the combination of natural gas and natural gas turbines the supply favorite of most electric utilities in the 1990s. 

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