Electricity is generated in power stations and transported across the UK via the National Grid.
To move power around the National Grid:
The transfer of electrical energy via the grid is very efficient. When currents in a cable are higher, more energy is dissipated to the surroundings through heating. As high currents waste more energy than low currents, electrical power is transported around the grid at a high voltage and a low current.
A transformer is a device that can change the voltage of an alternating current (ac). A basic transformer is made from two coils of wire ‐ a primary coil from the ac input and a secondary coil leading to the ac output. The coils are not electrically connected. Instead, they are wound around an iron core. This is easily magnetised and can carry magnetic fields from the primary coil to the secondary coil.
Step-up transformers are used to increase or 'step-up' voltages. These are used when electrical power output at the power station is stepped up from 25,000 V to 275,000 V or 400,000 V for transportation around the UK. A step-up transformer has more turns of wire on its secondary coil than it does on its primary coil. Transformers will only work with an alternating current (ac) input. This transformer steps up the voltage by reducing the current.
Step-down transformers are used to decrease or 'step-down' voltages. These are used when voltages need to be lowered for use in homes and factories. A step-down transformer has fewer turns of wire on the secondary coil than on the primary coil. This transformer steps down the voltage by increasing the current.