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Conejo; Claudio Canizares.
Electric Energy Systems: Analysis and Operation (Electric Power Engineering) - PDF Free Download
CRC Press, Tape repair present. Otherwise, minor shelf wear. Binding is tight and inside appears free from writing. Bookseller: the-book-life , Missouri, United States Seller rating:. Budapest perfected the secondary generator of Gaulard and Gibbs, providing it with a closed iron core, and thus obtained the first true power transformer, which he dubbed with its present name.
Kennedy in , in which several power transformers have their primary windings fed in parallel from a high-voltage distribution line. The system was presented at the National General Exhibition of Budapest.
Electrical Power Systems, Analysis and Operation
In George Westinghouse , an American entrepreneur, obtained the patent rights to the Gaulard-Gibbs transformer and imported a number of them along with a Siemens generator, and set his engineers to experimenting with them in hopes of improving them for use in a commercial power system.
In , one of Westinghouse's engineers, William Stanley , also recognised the problem with connecting transformers in series as opposed to parallel and also realised that making the iron core of a transformer a fully enclosed loop would improve the voltage regulation of the secondary winding. By , the electric power industry was flourishing, and power companies had built thousands of power systems both direct and alternating current in the United States and Europe.
These networks were effectively dedicated to providing electric lighting. During this time the rivalry between Thomas Edison and George Westinghouse's companies had grown into a propaganda campaign over which form of transmission direct or alternating current was superior, a series of events known as the " War of Currents ". In , after a protracted decision-making process, alternating current was chosen as the transmission standard with Westinghouse building the Adams No.
Developments in power systems continued beyond the nineteenth century. In the first experimental high voltage direct current HVDC line using mercury arc valves was built between Schenectady and Mechanicville, New York.
It consisted of a layer of selenium applied on an aluminum plate. In , a General Electric research group developed a solid-state p-n-p-n switch device that was successfully marketed in early , starting a revolution in power electronics. In , also Siemens demonstrated a solid-state rectifier, but it was not until the early s that solid-state devices became the standard in HVDC, when GE emerged as one of the top suppliers of thyristor-based HVDC.
For example, the development of computers meant load flow studies could be run more efficiently allowing for much better planning of power systems. Advances in information technology and telecommunication also allowed for remote control of a power system's switchgear and generators. Electric power is the product of two quantities: current and voltage.
These two quantities can vary with respect to time AC power or can be kept at constant levels DC power. Most refrigerators, air conditioners, pumps and industrial machinery use AC power whereas most computers and digital equipment use DC power digital devices plugged into the mains typically have an internal or external power adapter to convert from AC to DC power. AC power has the advantage of being easy to transform between voltages and is able to be generated and utilised by brushless machinery. DC power remains the only practical choice in digital systems and can be more economical to transmit over long distances at very high voltages see HVDC.
The ability to easily transform the voltage of AC power is important for two reasons: Firstly, power can be transmitted over long distances with less loss at higher voltages. So in power systems where generation is distant from the load, it is desirable to step-up increase the voltage of power at the generation point and then step-down decrease the voltage near the load.
Secondly, it is often more economical to install turbines that produce higher voltages than would be used by most appliances, so the ability to easily transform voltages means this mismatch between voltages can be easily managed. Solid state devices , which are products of the semiconductor revolution, make it possible to transform DC power to different voltages , build brushless DC machines and convert between AC and DC power.
Nevertheless, devices utilising solid state technology are often more expensive than their traditional counterparts, so AC power remains in widespread use. One of the main difficulties in power systems is that the amount of active power consumed plus losses should always equal the active power produced.
Applied Mathematics for Restructured Electric Power Systems
If more power is produced than consumed the frequency wil rise and vice versa. Even small deviations from the nominal frequency value will damage synchronous machines and other appliances. Making sure the frequency is constant is usually the task of a transmission system operator. In some countries for example in the European Union this is achieved through a balancing market using ancillary services. All power systems have one or more sources of power.
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- Electrical Power Systems, Analysis and Operation | Victoria University | Melbourne Australia.
For some power systems, the source of power is external to the system but for others, it is part of the system itself—it is these internal power sources that are discussed in the remainder of this section. Direct current power can be supplied by batteries , fuel cells or photovoltaic cells.
Alternating current power is typically supplied by a rotor that spins in a magnetic field in a device known as a turbo generator. There have been a wide range of techniques used to spin a turbine's rotor, from steam heated using fossil fuel including coal, gas and oil or nuclear energy , falling water hydroelectric power and wind wind power. The speed at which the rotor spins in combination with the number of generator poles determines the frequency of the alternating current produced by the generator.
All generators on a single synchronous system, for example, the national grid , rotate at sub-multiples of the same speed and so generate electric current at the same frequency. If the load on the system increases, the generators will require more torque to spin at that speed and, in a typical power station, more steam must be supplied to the turbines driving them. Thus the steam used and the fuel expended are directly dependent on the quantity of electrical energy supplied.
An exception exists for generators incorporating power electronics such as gearless wind turbines or linked to a grid through an asynchronous tie such as a HVDC link — these can operate at frequencies independent of the power system frequency. Depending on how the poles are fed, alternating current generators can produce a variable number of phases of power. A higher number of phases leads to more efficient power system operation but also increases the infrastructure requirements of the system.
However, there are other considerations. These range from the obvious: How much power should the generator be able to supply? What is an acceptable length of time for starting the generator some generators can take hours to start? Is the availability of the power source acceptable some renewables are only available when the sun is shining or the wind is blowing? To the more technical: How should the generator start some turbines act like a motor to bring themselves up to speed in which case they need an appropriate starting circuit?
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What is the mechanical speed of operation for the turbine and consequently what are the number of poles required? What type of generator is suitable synchronous or asynchronous and what type of rotor squirrel-cage rotor, wound rotor, salient pole rotor or cylindrical rotor? Power systems deliver energy to loads that perform a function. These loads range from household appliances to industrial machinery. Most loads expect a certain voltage and, for alternating current devices, a certain frequency and number of phases. An exception exists for larger centralized air conditioning systems as in some countries these are now typically three-phase because this allows them to operate more efficiently.
All electrical appliances also have a wattage rating, which specifies the amount of power the device consumes. At any one time, the net amount of power consumed by the loads on a power system must equal the net amount of power produced by the supplies less the power lost in transmission. Making sure that the voltage, frequency and amount of power supplied to the loads is in line with expectations is one of the great challenges of power system engineering.
However it is not the only challenge, in addition to the power used by a load to do useful work termed real power many alternating current devices also use an additional amount of power because they cause the alternating voltage and alternating current to become slightly out-of-sync termed reactive power. The reactive power like the real power must balance that is the reactive power produced on a system must equal the reactive power consumed and can be supplied from the generators, however it is often more economical to supply such power from capacitors see "Capacitors and reactors" below for more details.
A final consideration with loads is to do with power quality. In addition to sustained overvoltages and undervoltages voltage regulation issues as well as sustained deviations from the system frequency frequency regulation issues , power system loads can be adversely affected by a range of temporal issues. These include voltage sags, dips and swells, transient overvoltages, flicker, high-frequency noise, phase imbalance and poor power factor.
For DC supply, the ideal is the voltage not varying from a prescribed level. Power quality issues can be especially important when it comes to specialist industrial machinery or hospital equipment. Conductors carry power from the generators to the load. In a grid , conductors may be classified as belonging to the transmission system , which carries large amounts of power at high voltages typically more than 69 kV from the generating centres to the load centres, or the distribution system , which feeds smaller amounts of power at lower voltages typically less than 69 kV from the load centres to nearby homes and industry.
Choice of conductors is based on considerations such as cost, transmission losses and other desirable characteristics of the metal like tensile strength. Copper , with lower resistivity than aluminum , was the conductor of choice for most power systems. However, aluminum has a lower cost for the same current carrying capacity and is the primary metal used for transmission line conductors.
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