Why do power companies transmit three-phase power at high voltages?

Transmitting three-phase power at high voltages is primarily done to minimize power losses over long distances. When electrical power is transmitted, resistance in the transmission lines causes some of the energy to be lost as heat. The power loss due to resistance can be calculated using the formula ( P_{loss} = I^2R ), where ( I ) is the current and ( R ) is the resistance. By increasing the transmission voltage, the current flowing through the conductors is reduced for the same amount of power delivery. This reduction in current results in significantly lower power losses since losses depend on the square of the current.

Additionally, operating at high voltages allows for more efficient, economical transmission over vast distances, making it possible to connect remote generation sources (like hydroelectric or wind farms) to urban areas where demand is high. While considerations like improving voltage quality, reducing equipment size, or increasing current output may play a role in overall system design or operation, the primary factor for transmitting three-phase power at high voltages remains the substantial decrease in power losses.