Reason For High-voltage Transmission of Electricity
In electric power transmission, high voltage is used to reduce Joule heating of the overhead power lines. The valuable electric energy is intended to be used by consumers, not for pointlessly heating the power lines. Therefore this Joule heating is referred to as a type of transmission loss.
The power station wants to transfer a certain amount of electrical power Pload through power lines. (Pload represents the power used by all the elevators, televisions, etc. served by the station.) Since (ignoring phase difference, see AC power), it is possible to deliver the same power using a higher current at a lower voltage, or a lower current at a higher voltage. Transformers can switch between one and the other method of power transmission.
Since, using very low current at a very high voltage is the best way to reduce the transmission loss associated with Joule heating of the power lines. This explains the use of high voltage in the electrical grid.
The formula seems to suggest, incorrectly, that high voltage increases transmission losses. However, it is important to use the correct V: V is the slight reduction in voltage between the two sides of the power line, also called "line drop"; V is not the "line voltage" relative to ground. The line drop decreases when the line voltage increases (for a fixed power transmission).
Read more about this topic: Joule Heating
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