Test your knowledge of the National Grid in this GCSE Physics quiz. Electricity is generated in power stations of various kinds - ones that burn fossil fuels, nuclear fuelled power stations, hydroelectric etc. In the early days of electricity generation, it was carried out by companies using small local power stations. If one of these broke down then all of the consumers would be without electricity until it was repaired. Some companies supplied AC and others supplied DC and there was no agreement about what voltage to use.
This changed just after the end of the First World War - in 1919, the government at the time realised that electricity generation and supply needed to be better organised. An Act of Parliament created electricity generating authorities who took over the existing small and inefficient power stations, replacing them with a smaller number of larger ones.
They were also to interconnect their systems so that power could be transferred around the country to where it was most needed. A few years later, another authority was created (the Central Electricity Board) which established the National Grid by connecting together the largest of the power stations.
The National Grid is an electricity transmission network which spans the whole of the United Kingdom. It distributes electricity to most homes and businesses in the UK. Some homes and small businesses are 'off grid' which means that they generate their own electricity, usually by using environmentally sensitive methods. The National Grid also has undersea interconnections to northern France, Northern Ireland, the Irish Republic, the Isle of Man and the Netherlands, with more planned for the future.
Power stations generate electricity at 25,000 V and they are connected to the National Grid via step-up transformers. This is because electricity is sent through the grid at 400,000 V, 275,000 V or 132,000 V. A step-up transformer is one that increases the voltage. If the electricity was sent into homes, offices, shops, factories etc at these voltages, it would be extremely dangerous to use. Where the electricity is distributed to consumers, step-down transformers are used, for example, the last transformer between your school or your home and the National Grid reduces the voltage to 230 V. Transformers will only work using AC, so power stations no longer generate DC.
The reason that electricity is transferred around the country at such high voltages is to reduce energy losses. At high voltages, it requires less current to transfer the electricity through the wires. A lower current means that less of the electrical energy is transferred into heat energy. The further that the electricity travels through the National Grid, the greater the loss of energy.