Archivo para enero 27th, 2016


Microturbina power plant

More recently, a new generation of very small gas turbines has entered the marketplace. Often referred to asmicroturbines, these units generate anywhere from about 500 watts to several hundred kilowatts. The figure illustrates the basic configuration including compressor, turbine, and permanent-magnet generator, in this case all mounted on a single shaft. Incoming air is compressed to three or four atmospheres of pressure and sent through a heat exchanger called arecuperator, where its temperature is elevated by the hot exhaust gases. By preheating the compressed incoming air, the recuperator helps boost the efficiency of the unit. The hot, compressed air is mixed with fuel in the combustion chamber and is burned. The expansion of hot gases through the turbine spins the compressor and generator. The exhaust is released to the atmosphere after transferring much of
its heat to the incoming compressed air in the recuperator.

Source:
Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004

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Typical Power Plant Power Output and End-Use Power Demands

In addition to economic benefits, other motivations helping to drive the transition toward small-scale, decentralized energy systems include increased concern for environmental impacts of generation, most especially those related to climate change, increased concern for the vulnerability of our centralized energy systems to terrorist attacks, and increased demands for electricity reliability in the digital economy.
A sense of the dramatic decrease in scale that is underway is provided in Table (top), in which a number of generation technologies are listed along with typical power outputs. For comparison, some examples of power demands of typical end uses are also shown. While the power ratings of some of the distributed generation options may look trivially small, it is the potentially large numbers of replicated small units that will make their contribution significant. For example, the U.S. auto industry builds around 6 million cars each year. If half of those were 60-kW fuel-cell vehicles, the combined generation capacity of
5-year’s worth of automobile production would be greater than the total installed capacity of all U.S. power plants.

Source:
Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004


Characteristics of Copper Wire

Wire size in the United States with diameter less than about 0.5 in. is specified by its American Wire Gage (AWG) number. The AWG numbers are based on wire resistance, which means that larger AWG numbers have higher resistance and hence smaller diameter. Conversely, smaller gage wire has larger diameter and, consequently, lower resistance. Ordinary house wiring is usually No. 12 AWG, which is roughly the diameter of the lead in an ordinary pencil. The largest wire designated with an AWG number is 0000, which is usually written 4/0, with a diameter of 0.460 in. For heavier wire, which is usually stranded (made up of many individual wires bundled together), the size is specified in the United States in thousands of circular mills (kcmil). For example, 1000-kcmil stranded copper wire for utility transmission lines is 1.15 in. in diameter and has a resistance of 0.076 ohms per mile. In countries using the metric system, wire size is simply specified by its diameter in millimeters. In Table gives some
values of wire resistance, in ohms per 100 feet, for various gages of copper wire at 68◦F. Also given is the maximum allowable current for copper wire clad in the most common insulation

Source:
Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004