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Electric power transmission is the technical name for the movement of bulk electricity from power-generating locations to local subsystems. This designation separates it from electricity distribution, the name for the power as it moves from local subsystems to customers. There are several methods used to move power from one location to another, but overhead lines that are owned by a power distribution company are the most common. Since it is impossible to actually store electricity for long periods, one of the key points for electric power transmission is matching the supply of power to the demand for power.
In most cases, power lines that are used for electric power transmission are easy to spot. These are the power lines that are thicker and higher than standard pole lines. An electric power transmission line is often supported by a metal pole or metal grid work, rather than the standard wooden pole. These lines are occasionally buried underground, particularly in urban areas, but the relative expense and potential hazards of underground lines limit this practice.
Overhead power lines used for electric power transmission are built differently than standard power lines. The inner conductor is made of aluminum rather than copper. This makes the line lighter and less expensive without sacrificing power conductivity. The conductive strands are occasionally interwoven with steel wires to increase their strength, but this is usually only done in areas where the line will be under constant stress. The wires are uninsulated, which is why they are placed so high in the air.
The majority of electric power transmission is done using a three-phase alternating current. This power transmission type works well for shorter distances, but requires very expensive hardware. A single-phase alternating current is common when the power is going directly to a consumer, such as an electrified transportation system, rather than a local subsystem. Over long distances or when sending a cable through the water, high-voltage direct current is the preferred method.
The biggest point of concern for an electric power transmission system is matching the supply and demand for power. All of the power sent into the power grid needs to be used. If it isn’t, it can result in overloads and power outages at the weakest point within the distribution chain. If the grid demands more power than is supplied, the results are blackouts in high-usage areas.
To combat this problem, most power grids use several redundant electric power transmission methods. The power has other grids it can jump to if needed, and there are several different locations that a local grid may draw power from. This means that when one grid has too much or too little power, it can work with adjacent systems to equalize. If this system is overloaded, the results are often a large-scale blackout occasionally resulting in thousands, or even millions, of people with no power.