The National Grid
Electricity is generated in power stations and transported across the UK via the The network that connects all of the power stations in the country to make sure that everywhere has access to electricity..
To move power around the National Grid:
- before electrical power leaves a power station it is transferred at high voltages by using 'step-up' An electrical device that increases, or decreases, the potential difference (voltage) of an alternating current. to increase the voltage to 275,000 V or 400,000 V
- before electrical power enters homes and factories the voltages are decreased by 'step-down' transformers to 33,000 V (large factories), 11,000 V (medium factories), 230 V (homes, shops, small factories and offices)
The transfer of electrical energy via the grid is very efficient. When currents in a cable are higher, more energy is Transferred to the surroundings. 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.
Learn more on the National Grid in this podcast
Listen to the full series on 大象传媒 Sounds.
Step-up transformers
A transformer is a device that can change the The potential difference across a cell, electrical supply or electrical component. It is measured in volts (V). of an alternating current (ac). A basic transformer is made from two coils of wire 鈥 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 Area surrounding a magnet that can exert a force on magnetic materials. 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
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.