The UK's power stations, coal, gas, oil, hydro and renewable all supply electricity into the National Grid System. The electricity supplied is in the form of an alternating current (ac). In the UK, the mains electrical supply is generated at a frequency of 50 Hertz (Hz) and is delivered to houses at 230 Volts (V).
The National Grid distributes electricity across the country. The National Grid connects power stations to homes, workplaces and public buildings all around the country. The electricity may be produced by a conventional power station burning fossil fuels to heat water. The steam then drives turbines that will then turn a generator or by other methods using water and wind turbines.
Transformers are used to change voltages and currents in transmission lines. A transformer is formed from two coils of wire around an iron core. The coil ratio between the primary and secondary determines whether the transformers will step-up or step-down the voltage.
As the power transferred must stay the same:
In the National Grid, a step-up transformer is used to increase the voltage and reduce the current. The voltage is increased from about 25,000 volts (V) to 400,000 V causing the current to decrease. Less current means less energy is lost through heating the wire.
To keep people safe from these high voltage wires, pylons are used to support transmission lines above the ground.
These very high voltages are reduced in stages to a safer level of 230 V for the consumer using step-down transformers.
As an electric current flows through the steel reinforced aluminium cables held up by the pylons, they will get hotter and dissipate energy to the surroundings. The electrical power dissipated depends on current and resistance:
power = current2 × resistance
This is when:
To ensure that the minimum amount of power is lost from the cables:
A low resistance and a low current mean that the transmission cables will not heat up as much. As a result, most of the power is delivered to the consumer, and not dissipated as heat in the cables.