ELECTRIC POWER GENERATION, TRANSMISSION, AND. ELECTRIC POWER GENERATION, TRANSMISSION, AND. PDF) This book contains information obtained from authentic and. Transmission and Distribution Electrical Engineering By Colin Bayliss, Brian Hardy: Format: PDF: Size.
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Electric power transmission - Wikipedia. Two- circuit, single- voltage power transmission line; . The interconnected lines which facilitate this movement are known as a transmission network. This is distinct from the local wiring between high- voltage substations and customers, which is typically referred to as electric power distribution.
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The combined transmission and distribution network is known as the . In the United Kingdom, the network is known as the . For example, there are four major interconnections in North America (the Western Interconnection, the Eastern Interconnection, the Quebec Interconnection and the Electric Reliability Council of Texas (ERCOT) grid), and one large grid for most of continental Europe. The same relative frequency, but almost never the same relative phase as ac power interchange is a function of the phase difference between any two nodes in the network, and zero degrees difference means no power is interchanged; any phase difference up to 9. High- voltage direct- current (HVDC) technology is used for greater efficiency over very long distances (typically hundreds of miles).
HVDC technology is also used in submarine power cables (typically longer than 3. HVDC links are used to stabilize large power distribution networks where sudden new loads, or blackouts, in one part of a network can result in synchronization problems and cascading failures.
Power is usually transmitted through overhead power lines. Underground power transmission has a significantly higher installation cost and greater operational limitations, but reduced maintenance costs. Underground transmission is sometimes used in urban areas or environmentally sensitive locations. A lack of electrical energy storage facilities in transmission systems leads to a key limitation.
Electrical energy must be generated at the same rate at which it is consumed. A sophisticated control system is required to ensure that the power generation very closely matches the demand. If the demand for power exceeds supply, the imbalance can cause generation plant(s) and transmission equipment to automatically disconnect and/or shut down to prevent damage.
In the worst case, this may lead to a cascading series of shut downs and a major regional blackout. Examples include the US Northeast blackouts of 1. US regions in 1. 99. Electric transmission networks are interconnected into regional, national, and even continent wide networks to reduce the risk of such a failure by providing multiple redundant, alternative routes for power to flow should such shut downs occur. Transmission companies determine the maximum reliable capacity of each line (ordinarily less than its physical or thermal limit) to ensure that spare capacity is available in the event of a failure in another part of the network.
Overhead transmission. The conductor consists of seven strands of steel surrounded by four layers of aluminium. High- voltage overhead conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands.
Copper was sometimes used for overhead transmission, but aluminum is lighter, yields only marginally reduced performance and costs much less. Overhead conductors are a commodity supplied by several companies worldwide. Improved conductor material and shapes are regularly used to allow increased capacity and modernize transmission circuits. Conductor sizes range from 1. American wire gauge) to 7. Thicker wires would lead to a relatively small increase in capacity due to the skin effect, that causes most of the current to flow close to the surface of the wire. Because of this current limitation, multiple parallel cables (called bundle conductors) are used when higher capacity is needed.
Bundle conductors are also used at high voltages to reduce energy loss caused by corona discharge. Today, transmission- level voltages are usually considered to be 1. V and above. Lower voltages, such as 6. V and 3. 3 k. V, are usually considered subtransmission voltages, but are occasionally used on long lines with light loads. Voltages less than 3. V are usually used for distribution.
Voltages above 7. V are considered extra high voltage and require different designs compared to equipment used at lower voltages. Since overhead transmission wires depend on air for insulation, the design of these lines requires minimum clearances to be observed to maintain safety. Adverse weather conditions, such as high wind and low temperatures, can lead to power outages.
Wind speeds as low as 2. Underground cables take up less right- of- way than overhead lines, have lower visibility, and are less affected by bad weather. However, costs of insulated cable and excavation are much higher than overhead construction. Faults in buried transmission lines take longer to locate and repair. Underground lines are strictly limited by their thermal capacity, which permits less overload or re- rating than overhead lines. Long underground AC cables have significant capacitance, which may reduce their ability to provide useful power to loads beyond 5.
Long underground DC cables have no such issue and can run for thousands of miles. History. Besides telegraph lines, multiple electric lines were required for each class of device requiring different voltages. In the early days of commercial electric power, transmission of electric power at the same voltage as used by lighting and mechanical loads restricted the distance between generating plant and consumers. In 1. 88. 2, generation was with direct current (DC), which could not easily be increased in voltage for long- distance transmission. Different classes of loads (for example, lighting, fixed motors, and traction/railway systems) required different voltages, and so used different generators and circuits.
It seemed, at the time, that the industry would develop into what is now known as a distributed generation system with large numbers of small generators located near their loads. It was powered by a 2. V, 1. 30. Hz Siemens & Halske alternator and featured several Gaulard secondary generators with their primary windings connected in series, which fed incandescent lamps. The system proved the feasibility of AC electric power transmission on long distances. It was powered by two Siemens & Halske alternators rated 3. W), 2. 00. 0- V at 1. Hz and used 2. 00 series- connected Gaulard 2.
V/2. 0- V step- down transformers provided with a closed magnetic circuit, one for each lamp. Few months later it was followed by the first British AC system, which was put into service at the Grosvenor Gallery, London. It also featured Siemens alternators and 2. V/1. 00- V step- down transformers, one per user, with shunt- connected primaries. Powered by a steam engine driven 5. V Siemens generator, voltage was stepped down to 1.
Stanley transformer to power incandescent lamps at 2. The design, an induction motor running on polyphase current, was independently invented by Galileo Ferraris and Nikola Tesla (with Tesla's design being licensed by Westinghouse in the US). This design was further developed into the modern practical three- phase form by Mikhail Dolivo- Dobrovolsky and Charles Eugene Lancelot Brown. These companies continued to develop AC systems but the technical difference between direct and alternating current systems would follow a much longer technical merger. These included single phase AC systems, poly- phase AC systems, low voltage incandescent lighting, high voltage arc lighting, and existing DC motors in factories and street cars. In what was becoming a universal system, these technological differences were temporarily being bridged via the development of rotary converters and motor.
Such polyphase innovations revolutionized transmission. The first transmission of three- phase alternating current using high voltage took place in 1. Frankfurt. A 1. 5,0. V transmission line, approximately 1.
Lauffen on the Neckar and Frankfurt. By 1. 91. 4, fifty- five transmission systems each operating at more than 7. V were in service. The highest voltage then used was 1.
V. 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 Pacifi. Corp Hale Substation, Orem, Utah, USAEngineers 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.