The National Grid

The National Grid in the UK is a massive system of cables and transformers. It is designed to transport electricity across the country, carrying it from power stations (power plants) to homes, factories and businesses that require it.

Diagram depicting the flow of electricity from generation to household consumption. Starting on the left, a power plant with smokestack emits a plume of smoke. The electricity generated at the plant is directed to a generator, which then feeds it to a 'Step up transformer'. From here, electricity travels via 'High voltage cables' held aloft by a pylon. The current is then passed through a 'Step down transformer'. Finally, before reaching households, it is moderated by a 'Pole mounted transformer that reduces voltage for homes', leading to a representation of a residential house on the right.

High Voltage Transmission

Power stations/plants produce electricity, which can then be transmitted at different voltages and currents. When transmitting electricity over long distances, the current will experience great resistance. This means that high currents can heat the wires which causes energy loss in the form of thermal energy.

Let’s look at the equation P = V × I (Power = Voltage × Current). We can increase the voltage and decrease the current at the same ratio, which will keep the power the same. Therefore, by using a smaller current, we can transmit the same amount of power. This decreases the energy loss and is also much cheaper.


A transformer is an electrical device that changes the potential difference (voltage) of an alternating current supply. Transformers are used in transmission lines to adjust the voltage.

A basic transformer consists of two coils of wire, which are not connected together. Both coils are wound around a common iron core.

Diagram illustrating the difference between 'Step Up' and 'Step Down' transformers. On the left, the 'Step Up' transformer shows alternating current (AC) flowing through a primary coil and inducing AC in a secondary coil with more turns, resulting in an increase in voltage and current. An iron core connects the two coils. On the right, the 'Step Down' transformer displays AC passing through a primary coil, with the secondary coil having fewer turns, leading to a reduction in voltage and current. This, too, is connected by an iron core.

In the National Grid:

Step-up transformers increase the voltage and decrease the current as the electricity leaves the power station. They have more turns of wire on the secondary coil than on the primary coil.

Step-down transformers decrease the voltage and increase the current as the electricity reaches homes, factories or businesses. They have fewer turns of wire on the secondary coil than on the primary coil.

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