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TRANSMISSION LINES

Due to current technological limitations, large amounts of

electricity cannot be stored effectively therefore; it must be

produced when needed. A complicated control system is used to

manage the supply of electricity, keeping it at close to demand as

possible. Poor handling of the supply-demand gap could lead to

blackout (when demand exceeds supply).

Electricity is transferred from the plant to high voltage substations,

through a complex network of power lines, called a grid (UK

national grid). Energy is lost, due to electrical resistance, which

varies with material, when transmitting electricity over long

distances. To reduce this, electricity is transmitted at voltages of

120kV or higher (the voltage is stepped up from the plant output,

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which is usually between 2.3kV and 30kV). The actual lines are

usually transfer the stepped-up three-phase generator AC current,

however, DC current looses much less energy over long distances

than AC so high-voltage direct current (HVDC) lines are used for

greater distances (usually hundreds of miles).

Transmission lines are bundles of air-cooled individual conductors,

usually reinforced with steel strands for strength. Aluminum is the

material of choice for the conductors as it is lighter and cheaper

than copper and yields only marginally reduced performance. The

conductors are bundled to correct for skin effect. When current

flows in a cable, it tends to flow very close to the surface. The effect

is negligible for small cable radii, but at large radii most of the

radius of the wire is wasted thus multiple small radii conductors

(12mm2 to 750mm2) arranged parallel to each other, resulting in a

significant increase in the current carrying capacity of the

transmission line.

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There are different transmission lines with different operating

voltages (i.e. the voltage at which electricity is transmitted along

that line). The voltage given with a particular transmission line is

its operating voltage, e.g. 330kV.

REFERENCE:

1. "Transformer." Wikipedia. Wikimedia Foundation, 16 June

2014. Web. [Accessed 16 June 2014].

2. "Electric Power Transmission." Wikipedia. Wikimedia

Foundation, 15 June 2014. Web. [Accessed 16 June 2014].