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Electrical transmission and distribution reference book. byWestinghouse Electric Westinghouse electric & manufacturing company. Get this from a library! Electrical transmission and distribution reference book. [ Westinghouse Electric Corporation.]. Results 1 - 26 of 26 Electrical Transmission and Distribution Reference Book. The Central Station Engineers Of Westinghouse. Published by Westinghouse.
Energy is usually transmitted within a grid with three-phase AC. Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors. Higher order phase systems require more than three wires, but deliver little or no benefit.
The synchronous grids of the European Union The price of electric power station capacity is high, and electric demand is variable, so it is often cheaper to import some portion of the needed power than to generate it locally. Because loads are often regionally correlated hot weather in the Southwest portion of the US might cause many people to use air conditioners , electric power often comes from distant sources.
Because of the economic benefits of load sharing between regions, wide area transmission grids now span countries and even continents. The web of interconnections between power producers and consumers should enable power to flow, even if some links are inoperative. The unvarying or slowly varying over many hours portion of the electric demand is known as the base load and is generally served by large facilities which are more efficient due to economies of scale with fixed costs for fuel and operation.
Such facilities are nuclear, coal-fired or hydroelectric, while other energy sources such as concentrated solar thermal and geothermal power have the potential to provide base load power. Renewable energy sources, such as solar photovoltaics, wind, wave, and tidal, are, due to their intermittency, not considered as supplying "base load" but will still add power to the grid. The remaining or 'peak' power demand, is supplied by peaking power plants , which are typically smaller, faster-responding, and higher cost sources, such as combined cycle or combustion turbine plants fueled by natural gas.
Hydro and wind sources cannot be moved closer to populous cities, and solar costs are lowest in remote areas where local power needs are minimal. Connection costs alone can determine whether any particular renewable alternative is economically sensible. Costs can be prohibitive for transmission lines, but various proposals for massive infrastructure investment in high capacity, very long distance super grid transmission networks could be recovered with modest usage fees.
Grid input[ edit ] At the power stations , the power is produced at a relatively low voltage between about 2. The Losses[ edit ] Transmitting electricity at high voltage reduces the fraction of energy lost to resistance , which varies depending on the specific conductors, the current flowing, and the length of the transmission line.
Measures to reduce corona losses include conductors having larger diameters; often hollow to save weight,  or bundles of two or more conductors.
Factors that affect the resistance, and thus loss, of conductors used in transmission and distribution lines include temperature, spiraling, and the skin effect. The resistance of a conductor increases with its temperature. Temperature changes in electric power lines can have a significant effect on power losses in the line. Spiraling, which refers to the way stranded conductors spiral about the center, also contributes to increases in conductor resistance. The skin effect causes the effective resistance of a conductor to increase at higher alternating current frequencies.
Corona and resistive losses can be estimated using a mathematical model. As of , the longest cost-effective distance for direct-current transmission was determined to be 7, kilometres 4, miles. For alternating current it was 4, kilometres 2, miles , though all transmission lines in use today are substantially shorter than this.
These reactive currents, however, are very real and cause extra heating losses in the transmission circuit.
The ratio of 'real' power transmitted to the load to 'apparent' power the product of a circuit's voltage and current, without reference to phase angle is the power factor. As reactive current increases, the reactive power increases and the power factor decreases. For transmission systems with low power factor, losses are higher than for systems with high power factor.
Utilities add capacitor banks, reactors and other components such as phase-shifting transformers ; static VAR compensators ; and flexible AC transmission systems , FACTS throughout the system help to compensate for the reactive power flow, reduce the losses in power transmission and stabilize system voltages. These measures are collectively called 'reactive support'. Transposition[ edit ] Current flowing through transmission lines induces a magnetic field that surrounds the lines of each phase and affects the inductance of the surrounding conductors of other phases.
The mutual inductance of the conductors is partially dependent on the physical orientation of the lines with respect to each other. Three-phase power transmission lines are conventionally strung with phases separated on different vertical levels. The mutual inductance seen by a conductor of the phase in the middle of the other two phases will be different than the inductance seen by the conductors on the top or bottom.
An imbalanced inductance among the three conductors is problematic because it may result in the middle line carrying a disproportionate amount of the total power transmitted.
Similarly, an imbalanced load may occur if one line is consistently closest to the ground and operating at a lower impedance. Because of this phenomenon, conductors must be periodically transposed along the length of the transmission line so that each phase sees equal time in each relative position to balance out the mutual inductance seen by all three phases.
To accomplish this, line position is swapped at specially designed transposition towers at regular intervals along the length of the transmission line in various transposition schemes. It is uneconomical to connect all distribution substations to the high main transmission voltage, because the equipment is larger and more expensive.
Typically, only larger substations connect with this high voltage. It is stepped down and sent to smaller substations in towns and neighborhoods. Subtransmission circuits are usually arranged in loops so that a single line failure does not cut off service to a large number of customers for more than a short time.
Loops can be "normally closed", where loss of one circuit should result in no interruption, or "normally open" where substations can switch to a backup supply.
While subtransmission circuits are usually carried on overhead lines , in urban areas buried cable may be used. The lower-voltage subtransmission lines use less right-of-way and simpler structures; it is much more feasible to put them underground where needed.
Higher-voltage lines require more space and are usually above-ground since putting them underground is very expensive. There is no fixed cutoff between subtransmission and transmission, or subtransmission and distribution. The voltage ranges overlap somewhat. As power systems evolved, voltages formerly used for transmission were used for subtransmission, and subtransmission voltages became distribution voltages.
Like transmission, subtransmission moves relatively large amounts of power, and like distribution, subtransmission covers an area instead of just point-to-point. Finally, at the point of use, the energy is transformed to low voltage varying by country and customer requirements — see Mains electricity by country. Advantage of high-voltage power transmission[ edit ] See also: ideal transformer High-voltage power transmission allows for lesser resistive losses over long distances in the wiring.
This efficiency of high voltage transmission allows for the transmission of a larger proportion of the generated power to the substations and in turn to the loads, translating to operational cost savings. Electrical grid without a transformer.
Electrical grid with a transformer. In a very simplified model, assume the electrical grid delivers electricity from a generator modelled as an ideal voltage source with voltage V. Some features of WorldCat will not be available. Create lists, bibliographies and reviews: Search WorldCat Find items in libraries near you.
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East Pittsburgh, Pa. Subjects Electric power distribution. Electric lines. More like this Similar Items. Allow this favorite library to be seen by others Keep this favorite library private. Find a copy in the library Finding libraries that hold this item