Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!


Transmitting electricity


  1. 1
  2. 2
  1. Next

Electricity is generated when a coil of wire moves in a magnetic field. This is the basis of electricity generators.

Most electricity is made in power stations by burning fuels. Transformers are used in the National Grid to reduce energy losses from the wires during transmission.

The National Grid and transformers


A transformer is an electrical device that changes the voltage of an AC supply. A transformer changes a high-voltage supply into a low-voltage one, or vice versa.

  • A transformer that increases the voltage is called a step-up transformer
  • A transformer that decreases the voltage is called a step-down transformer

Step-down transformers are used in mains adapters and rechargers for mobile phones and CD players.

The National Grid

When a current flows through a wire, some energy is lost as heat. The higher the current, the more heat is lost. The National Grid transmits electricity at a low current to reduce these losses. This requires a high voltage.

Power stations produce electricity at 25,000V. Electricity is sent through the National Grid cables at 400,000V, 275,000V and 132,000V.

Step-up transformers at power stations produce the very high voltages needed to transmit electricity through the National Grid power lines. This is because high voltages improve efficiency by reducing heat loss in the power lines. But high voltages are too dangerous for use in the home, so step-down transformers are used locally to reduce the voltage to safe levels. Power lines and substations are potentially dangerous as an electric shock can kill someone who gets too close to such a high voltage supply.

read on if you're taking the higher paper.


  1. 1
  2. 2
  1. Next

Back to Generation and transmission of electricity index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.