# AC transmission

High-voltage overhead lines carrying bulk power over long distances, up to ultra-high voltage.

Source page: https://www.materialinsights.org/energy/e_hvac/

Transport · Electricity · No. 50

- Transport
- Form: Electricity
 Transport · Electricity · Foundation · Energy

The world's power lines stretch about 80 million km, and electricity crosses 1,000 km of them in about 3 milliseconds.

Chart: Illustration: AC transmission

##### Where it comes from

Chart: Map of where it comes from

Power stations make alternating current. A transformer lifts it to 345, 500 or 765 kV so the same power flows with far less current, and overhead lines carry it to cities.

##### Three things to know

1. Doubling the voltage halves the current and cuts heating losses to about a quarter, which is why lines run at hundreds of kilovolts.
2. Power lines in the US kill an estimated 8 to 57 million birds a year in collisions.
3. Lead times for large power transformers have almost doubled since 2021, to as long as 4 years.

##### The journey

1. 1 **Generator**Makes AC reversing 50-60 times a second
2. 2 **Step-up**Transformer raises voltage to 345-765 kV
3. 3 **Overhead line**Aluminium-steel conductors on steel towers
4. 4 **Substation**Breakers route power and isolate faults
5. 5 **Step-down**Voltage lowered for local networks
 Covered in [Power density: why land and space matterEnergy](https://www.materialinsights.org/learn/energy/power-density/)[Moving energy: wires, pipes and shipsEnergy](https://www.materialinsights.org/learn/energy/moving-energy/)

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## Other sections

- [Overview](https://www.materialinsights.org/energy/e_hvac/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_hvac/correlation/index.md)
- [How it works](https://www.materialinsights.org/energy/e_hvac/explain/index.md)
- [Efficiency and losses](https://www.materialinsights.org/energy/e_hvac/efficiency/index.md)
- [Technology advances](https://www.materialinsights.org/energy/e_hvac/advances/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_hvac/valuechain/index.md)
- [Geopolitics and regulation](https://www.materialinsights.org/energy/e_hvac/geopolitics/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_hvac/economics/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_hvac/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_hvac/links/index.md)