20.9 - National Grid
Transmitting at high potential difference
- Transmitting electricity at a high current causes the cables to heat up, wasting energy as heat to the surroundings (P = I2R).
- Electrical power is given by P = IV, so for a given power, increasing the potential difference lowers the current.
- Transmitting at a very high potential difference (around 400,000 V) keeps the current low, minimising thermal energy loss and making the grid much more efficient.
Step-up and step-down transformers
- Transformers change the potential difference of the alternating current on the National Grid.
- Step-up transformers increase the potential difference to around 400,000 V as electricity leaves the power station. This decreases the current, reducing energy wasted as heat in the transmission cables.
- Step-down transformers decrease the potential difference to safe, usable levels (230 V in UK homes) before electricity reaches consumers.
TermDefinition
TransformerA device that changes the size of an alternating potential difference (voltage).
Step-up transformerA transformer that increases the potential difference (voltage) and decreases the current. It has more turns on its secondary coil than on its primary coil.
Step-down transformerA transformer that decreases the potential difference (voltage) and increases the current. It has fewer turns on its secondary coil than on its primary coil.