There are several types of three-phase lines commonly used in electrical power systems:
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Overhead Lines: These consist of conductors suspended above the ground on towers or poles. They are often used for long-distance power transmission due to their relatively low cost and ease of installation. Overhead lines can be made of aluminum or copper conductors and are exposed to the elements.
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Underground Cables: These are buried beneath the ground and offer protection from the environment and less visual impact. Underground cables can be of various types, such as XLPE (Cross-linked Polyethylene) insulated cables or oil-filled cables. They are commonly used in urban areas or where aesthetics and space limitations are a concern.
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Bundled Conductors: In some cases, multiple conductors are grouped together in a bundle to reduce electrical losses and increase the power-carrying capacity of the line. This is common in high-voltage transmission systems.
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Shielded Lines: These have a shielding layer around the conductors to reduce electromagnetic interference and improve the line's performance in sensitive areas.
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High-Voltage Direct Current (HVDC) Lines: These are used for long-distance power transmission over very large distances. HVDC lines have unique converter stations at either end to convert the alternating current (AC) to direct current (DC) for transmission and then back to AC at the receiving end.
For example, in a rural area where land is readily available and cost is a factor, overhead lines might be the preferred choice for transmitting power from a power plant to a substation. In an urban setting, underground cables would be more suitable to avoid visual clutter and minimize the risk of outages due to weather or physical damage.
The type of three-phase line selected depends on factors such as the distance of transmission, power requirements, environmental conditions, and cost considerations.