High Tension Line
Steel grounded shield conductors at the tops of the towers significantly reduce, but do not eliminate, the probability of direct lightning strikes to phase conductors. These cables virtually eliminate negative environmental effects and reduce electrocution hazards. This value is not the total impedance of the line, but rather the series impedance per unit length of line. The semiconducting glaze also ensures a more even distribution of voltage along the length of the chain of insulator units. Thus, during bad weather, corona discharge is more intense and losses are much greater. Each phase of the line is built with two, three, or four conductors connected in parallel and separated by about 1.5 ft (0.5 m). In 2007, the World health organization (WHO) released a report that linked ELF radiation with higher possibility of childhood leukemia. Surface irregularities such as water droplets cause local field concentration, enhancing corona generation. Overhead line is designed on the principle of one or more overhead wires situated over rail tracks. A typical high-voltage line has three phase conductors to carry the current and transport the energy, and two grounded shield conductors to protect the line from direct lightning strikes. The operation of circuit breakers causes switching surges that can result in interruption of inductive current, energization of lines with trapped charges, and single-phase ground fault. The placement of power lines sometimes use up sites that would otherwise be used by hang gliders.The first transmission of electrical impulses over an extended distance was demonstrated on July 14, 1729 by the physicist However the first practical use of overhead lines was in the context of In 1912 the first 110 kV-overhead power line entered service followed by the first 220 kV-overhead power line in 1923. Compact transmission lines may be designed for voltage upgrade of existing lines to increase the power that can be transmitted on an existing right of way.Low voltage overhead lines may use either bare conductors carried on glass or ceramic insulators or an Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains. Conductors must not get too close to each other. Most cities use underground cables to distribute electrical energy. Water provides natural cooling, and pressure reduces the possibility of void formation. Bundle conductors reduce corona discharge. With operating voltages less than 34.5 kV, the distribution system carries energy from the local substation to individual households, using both overhead and underground lines. In the area surrounding the overhead lines, it is dangerous to risk interference, e.g. The overhead transmission line is generally categorized into three classes,This categorization is mainly done for the ease of performance analysis of transmission lines, by power engineers. This is a source of concern given the considerable fraction of the population that lives in close proximity to high-voltage, above-ground power lines, also known as high-tension wires.
It is treated as bare cable, but often is safer for wildlife, as the insulation on the cables increases the likelihood of a large-wing-span raptor to survive a brush with the lines, and reduces the overall danger of the lines slightly. In some cases, a large industrial customer may receive electricity directly from overhead transmission lines. Feeder stations at regular intervals along the overhead line supply power from the high-voltage grid. The normal distance between the supporting towers is a few hundred feet.Transmission lines use ACSR (aluminum cable, steel reinforced) and ACAR (aluminum cable, alloy reinforced) conductors. Low-pressure oil-filled cable construction reduces void formation. Medium-voltage distribution lines may also use one or two shield wires, or may have the grounded conductor strung below the phase conductors to provide some measure of protection against tall vehicles or equipment touching the energized line, as well as to provide a neutral line in Wye wired systems. Better pollution and wet performance is leading to the increased use of such insulators. In cases where these conditions are suboptimal, longer insulators must be used.
With operating voltage exceeding 230 kV, the transmission system interconnects generating stations and large substations located close to load centers by using overhead lines.Overhead transmission lines distribute the majority of the electric energy in the system. A single-phase concentric cable has a hollow conductor with a central oil channel.
A short circuit generates large currents, overheating conductors and producing permanent damage.The power that a line can transport is limited by the line's electrical parameters. The number of disks is chosen based on line voltage, lightning withstand requirement, altitude, and environmental factors such as fog, pollution, or salt spray. Bundled conductors reduce the voltage gradient in the vicinity of the line. For a longer length of line (80–250 km), a shunt capacitance is added to the model. The standard frequency in North America is 60 Hz; in Europe, 50 Hz. Longer insulators with longer creepage distance for leakage current, are required in these cases.
With operating voltages of 69-138 kV, the subtransmission system distributes energy within an entire district and regularly uses overhead lines. Depending on the design criteria for a particular line, semi-flexible type structures may rely on the weight of the conductors to be balanced on both sides of each tower. Structures may be as simple as wood Each structure must be designed for the loads imposed on it by the conductors.A large transmission line project may have several types of towers, with "tangent" ("suspension" or "line" towers, UK) towers intended for most positions and more heavily constructed towers used for turning the line through an angle, dead-ending (terminating) a line, or for important river or road crossings. Use of the area below an overhead line is limited because objects must not come too close to the energized conductors.
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