AC transmission
High-voltage overhead lines carrying bulk power over long distances, up to ultra-high voltage.
Transport · Electricity · No. 50
- Transport
- Form: Electricity
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
- Doubling the voltage halves the current and cuts heating losses to about a quarter, which is why lines run at hundreds of kilovolts.
- Power lines in the US kill an estimated 8 to 57 million birds a year in collisions.
- Lead times for large power transformers have almost doubled since 2021, to as long as 4 years.
The journey
- 1 GeneratorMakes AC reversing 50-60 times a second
- 2 Step-upTransformer raises voltage to 345-765 kV
- 3 Overhead lineAluminium-steel conductors on steel towers
- 4 SubstationBreakers route power and isolate faults
- 5 Step-downVoltage lowered for local networks