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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.
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More efficient inverters use various methods to produce an approximate sine wave at the transformer input rather than relying on the transformer to smooth it. Capacitors can be used to smooth the flow of current into and out of the transformer. It is also possible to produce a more sinusoidal wave by having split-rail direct current inputs at two voltages, positive and negative inputs with a central ground. By connecting the transformer input terminals in a timed sequence between the positive rail and ground, the positive rail and the negative rail, the ground rail and the negative rail, then both to the ground rail, a 'stepped sinusoid' is generated at the transformer input and the current drain on the direct current supply is less variable.
This output is converted to DC at the same voltage, and then inverted again to a quasi sine wave output about V RMS. A disadvantage of the modified sine wave inverters is that the output voltage depends on the battery voltage. It is quite difficult to obtain a good sine wave from an inverter. Batteries[ edit ] Most home systems use conventional lead acid batteries for storage.
They are cheap, and are deep cycle batteries, i. You cannot use automobile batteries in inverters, as they are only used to provide a large starting current, and are not meant to be discharged completely. The lead acid batteries have the disadvantage that they have to be replenished with distilled water every few months, and if it dries out, it cannot be repaired.
However, they can provide the large surge currents which are required by many loads such as induction motors which may be connected to the system. Switched Mode Power Supply[ edit ] Wikipedia has related information at DC to DC converter A switched-mode power supply, or SMPS or switching regulator, is an electronic power supply circuit that attempts to produce a smoothed, constant-voltage, output from a varying input voltage.
Switched-mode power supplies may be designed to convert from alternating current or direct current, or both. They generally output direct current, although an inverter is technically a switched-mode power supply. Switched-mode power supplies operate by using an inverter to convert the input direct current supply to alternating current, usually at around 20 kHz.
If the input is alternating current but at a lower frequency such as 50 Hz or 60 Hz line power then an inverter is still used to bump the frequency up. This high frequency means that the output transformer of the inverter will operate more efficiently than if it were run at 50 Hz or 60 Hz, due to hysteresis in the transformer core, and the transformer will not need to be as large or heavy.
This high-frequency output is then fed through a rectifier to produce the output direct current. Regulation is achieved through feedback. The output voltage is compared to a reference voltage and the result used to alter the switching frequency or duty cycle of the inverter oscillator, which affects its output voltage.
Switched-mode PSUs in domestic products such as personal computers often have universal inputs, meaning that they can accept power from most mains supplies throughout the world, with frequencies from 50 Hz to 60 Hz and voltages from V to V. Unlike most other appliances, switched mode power supplies tend to be constant power devices, drawing more current as the line voltage reduces.
This may cause stability problems in some situations such as emergency generator systems. Also, maximum current draw occurs at the peaks of the waveform cycle. This means that basic switched mode power supplies tend to produce more harmonics and have a worse power factor than other types of appliances. However, higher-quality switched-mode power supplies with power-factor correction PFC are available, which are designed to present close to a resistive load to the mains.
The term power factor with respect to switched-mode supplies is misleading as it doesn't have much to do with leading or lagging voltage, but the way in which it loads the circuit i.
There are several types of switched-mode power supplies, classified according to the circuit topology. Another common single-phase AC motor is the induction motor, commonly used in major appliances such as washing machines and clothes dryers. These motors can generally provide greater starting torque by using a special startup winding in conjunction with a starting capacitor and a centrifugal switch.
When starting, the capacitor and special winding are temporarily connected to the power source and provide starting torque. Once the motor reaches speed, the centrifugal switch disconnects the capacitor and startup winding.
Shaded-pole synchronous motor[ edit ] Shaded-pole synchronous motors are a class of AC motor that uses single phase electric power to convert electric power to mechanical energy. They work by using a squirrel-cage rotor and a split stator that has copper shorting rings placed on it so as to shade a portion of the stator's magnetic field enough to provide starting torque. The number of poles in an induction motor is an important factor in its interaction with non sine wave input.
As a rule of thumb, motors with larger number of poles are more sensitive to harmonic distortion. Incandescent Lamps[ edit ] Early applications of lighting was using lamps which used a heated filament to provide light.
The filament was made of tungsten and was placed inside a near vacuum glass enclosure. While it was cheap, it produced a lot of heat, so that it was inefficient too. Note that the incandescent bulb is a purely resistive load power factor 1. Wikipedia has related information at inrush current The incandescent bulb is designed to operate at high temperatures.
At normal operating temperatures, a tungsten filament has a resistance nearly 20 times its room-temperature resistance. So when a bulb is turned on, it draws a current nearly 20 times the normal current until it warms up. This current surge is called the inrush current, which lasts for milliseconds. Again, something different from the "dumb load" point of view. The highest voltage then used was kV. The most efficient available plants could be used to supply the varying loads during the day.
Reliability was improved and capital investment cost was reduced, since stand-by generating capacity could be shared over many more customers and a wider geographic area.
Remote and low-cost sources of energy, such as hydroelectric power or mine-mouth coal, could be exploited to lower energy production cost. The interconnection of local generation plants and small distribution networks was greatly spurred by the requirements of World War I , with large electrical generating plants built by governments to provide power to munitions factories.
Later these generating plants were connected to supply civil loads through long-distance transmission. It also reroutes power to other transmission lines that serve local markets. This is the PacifiCorp Hale Substation, Orem, Utah , USA Engineers design transmission networks to transport the energy as efficiently as feasible, while at the same time taking into account economic factors, network safety and redundancy. These networks use components such as power lines, cables, circuit breakers , switches and transformers.
The transmission network is usually administered on a regional basis by an entity such as a regional transmission organization or transmission system operator. Transmission efficiency is greatly improved by devices that increase the voltage and thereby proportionately reduce the current , in the line conductors, thus allowing power to be transmitted with acceptable losses.
The reduced current flowing through the line reduces the heating losses in the conductors. According to Joule's Law , energy losses are directly proportional to the square of the current. Thus, reducing the current by a factor of two will lower the energy lost to conductor resistance by a factor of four for any given size of conductor.
The optimum size of a conductor for a given voltage and current can be estimated by Kelvin's law for conductor size , which states that the size is at its optimum when the annual cost of energy wasted in the resistance is equal to the annual capital charges of providing the conductor.
At times of lower interest rates, Kelvin's law indicates that thicker wires are optimal; while, when metals are expensive, thinner conductors are indicated: however, power lines are designed for long-term use, so Kelvin's law has to be used in conjunction with long-term estimates of the price of copper and aluminum as well as interest rates for capital. The increase in voltage is achieved in AC circuits by using a step-up transformer. HVDC systems require relatively costly conversion equipment which may be economically justified for particular projects such as submarine cables and longer distance high capacity point-to-point transmission.
HVDC is necessary for the import and export of energy between grid systems that are not synchronized with each other. A transmission grid is a network of power stations , transmission lines, and substations.
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.