The primary reason that power is transmitted at high voltages is to increase efficiency. As electricity is transmitted over long distances, there are inherent energy losses along the way. ... The higher the voltage, the lower the current. The lower the current, the lower the resistance losses in the conductors.

Why are voltages stepped up before transmission?

Power companies use step-up transformers to boost the voltage to hundreds of kV before it is transmitted down a power line, reducing the current and minimizing the power lost in transmission lines. Step-down transformers are used at the other end, to decrease the voltage to the 120 V used in household circuits.

Why is high voltage used for long transmission lines?

High voltage transmission lines deliver electricity over long distances. The high voltage is required to reduce the amount of energy lost during the distance. Unlike other energy sources such as natural gas, electricity can't be stored when it is not used. If demand exceeds supply, a blackout occurs.