Why does raising the voltage reduce losses in a power line?

The same power flows as less current, and heat grows with current squared

A line is rebuilt at double the voltage but carries the same power. What happens to its heat loss?

It falls to a quarter of what it was before

What stops engineers from raising line voltage endlessly?

Past about 2,000 kV to ground, corona discharge losses offset the savings

Tech●●●●●

Why do power lines run at hundreds of thousands of volts?

A line that carries the same power at twice the voltage wastes four times less of it as heat.

▶ Start the story

Power lines use enormous voltages because of a simple trade. Electric power is voltage times current, so for a given amount of power, doubling the voltage delivers the same power at only half the current. And the current is what causes the damage: the heat that wires waste is proportional to the square of the current. Halve the current and you lose four times less energy to resistance. The line is a long, thin heater, and high voltage lets it run barely warm.

Real numbers show how big the effect is. A 100-mile (160 km) span at 765 kV carrying 1,000 megawatts can lose between 0.5 and 1.1 percent. A 345 kV line carrying the same load the same distance loses 4.2 percent. That is why power stations, which make electricity at only about 480 volts to 22 kilovolts, immediately use a transformer to raise it to 100 to 1,000 kilovolts for the trip.

Try it

Losses against voltage (a simple model)

y = 1 · x^−1

Exponent: how fast losses fall as voltage rises-1

Challenge · Set the exponent so that doubling the voltage (×2) leaves a quarter of the loss.

A simple model: with the same power, heat loss follows the square of the current, which falls as the voltage rises.

There is a human side to this. When Edison opened his first power station in 1882 it ran at a low 110 volts, and his plants needed to be within about 1.5 miles of the farthest customer or the copper would have had to be thicker and costlier. Each doubling of voltage lets a cable carry the same power four times as far. In 1891 engineers proved the idea at an exhibition in Frankfurt: a line at 15 kV, about 175 km long, carried power from Lauffen to the show.

Today's grids still lose a little on the way. US transmission and distribution losses were estimated at 5 percent from 2013 to 2019.

Quiz me

0/3

1.Why does raising the voltage reduce losses in a power line?
2.A line is rebuilt at double the voltage but carries the same power. What happens to its heat loss?
3.What stops engineers from raising line voltage endlessly?

Recap

Same power, higher voltage, lower current: and the loss falls with the square of the current.

💡 A trick to remember it · Push a crowd through a corridor as a few fast runners instead of many slow walkers, and far less gets rubbed off on the walls.

Surprising fact · A 765 kV line can lose 0.5% to 1.1% over 100 miles where a 345 kV line loses 4.2%.

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Sources (3)

No source, no claim. Every fact in this lesson (14 claims) cites at least one of these.

Why do power lines run at hundreds of thousands of volts?

Quiz me

Recap

How did a software bug and a tree black out 55 million people?

How does a transformer change voltage with no moving parts?

How does electricity get from a power plant to your plug?

One more light on your map.