The National Grid and Electricity Transmission — AQA GCSE Physics
The National Grid is a nationwide network of cables and transformers that distributes electricity efficiently.
The National Grid
The National Grid carries electrical power from power stations to homes, businesses and industry. It consists of cables, pylons and transformers.
Step-up and step-down transformers
- Step-up transformers are used at the power station to increase the potential difference (to a very high voltage, e.g. 400 000 V) for transmission.
- Step-down transformers are used near consumers to decrease the potential difference to safer, usable values (e.g. 230 V for homes).
Why use a high voltage?
For a given amount of power (P = VI), increasing the voltage means a lower current is needed. Energy lost as heat in the cables depends on the current², so a lower current means much less energy is wasted as heat. This makes transmission efficient over long distances.
Transformers and energy
For an ideal transformer, the power input equals the power output. Step-up transformers increase voltage but decrease current; step-down transformers do the reverse.
Exam tips
- The National Grid uses step-up (at power station) and step-down (near consumers) transformers.
- High voltage → low current → less energy wasted as heat in cables.
- This makes long-distance transmission efficient.
- For an ideal transformer, power in = power out.