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GB electricity transmission and distribution network - About

Electricity supply around the world is split up into three categories: generation; transmission; and distribution. Transmission and distribution are commonly overlooked as being the same thing; however there are quite distinct differences between the two. Below is an image illustrating the process of energy transportation in an easy to understand manner:

Electrical transmission process

So, in a nutshell...

  1. Generation: The electricity produced from the source e.g. power plants, wind turbines etc.
  2. In order to reduce resistance in transmission lines, the electricity is passed through a step-up transformer to increase the voltage and therefore reduce the current. This allows the electricity to be transported over large distances without losing as much electricity in the process.
  3. The electricity is transmitted across the country bidirectionally to allow the grid’s needs to be fulfilled. This reduces the risk of power cuts and allows electricity to be sent to where it is needed.
  4. Because the voltage of the transmission network is way too high to be distributed directly into homes and businesses, the electricity is passed through a step-down transformer to reduce the voltage.
  5. The electricity is now transferred to low voltage distribution lines that are managed by area-specific distribution companies. This electricity is now transported over small distances, usually within small localities.
  6. You can put the kettle on and watch your favourite tele programme.

Generation

Electricity in the UK comes from a large variety of sources. Although we are still heavily dependant on natural gas and coal, like the majority of countries worldwide, our energy mix is ever expanding, preventing us from becoming too reliant on any one source.

Power plant generation

One method in which we’ve seen rather large investment over recent years is nuclear power. Nuclear now constitutes around 20% of our electricity generation; however, this figure is set to decrease within the coming years due to the Paris Climate Agreement.

Renewable generation, which we have gone into greater detail on below, now makes up around 25% of all electricity.

This comes from such sources as: wind; solar; hydro; and biomass. Renewables are becoming an ever important asset to any country’s generation arsenal, many tipping them to become the future of world power. As such, the UK government have publicly declared their support for green generation, hoping to increase dependency on which to 30% by 2030.

Although the UK is slowly starting to phase out fossil fueled power plants, we are still burning large amounts of Co2 into the atmosphere.

We currently have around 300 power plants running in the UK, (a fair few that are abandoned too) including the largest polluter of Co2, Drax power station in Yorkshire.

Drax is the latest power station to be built, finishing its completion in 1986. Even though it is the biggest emitter of Co2, it is falling year on year as it increases its biomass production. Drax are transporting 2 meta tons of compressed wood pellets annually from the southern states of America to heat homes in the UK.

Fossil fuel generation

What happens when a power plant emits Co2? If we use coal and gas as an example, these fuels are put together into a furnace which starts the process of creating electricity.

The large furnace is connected via pipes to a tank of water where the water is heated, which creates steam to move the large turbines. Once the turbines start rotating from the rising steam, a shaft with magnets connected starts to spin and electricity is conducted.

Renewable generartion

Instead of burning coal or using nuclear fission to generate electricity, renewable sources, such as wind, solar and hydro power, are beginning to be used more in the UK. Many distributors, including SSE, are investing millions of pounds in offshore wind farms.

Offshore wind farm

The site of Beatrice offshore wind farm

The beatrice wind farm is a project currently under construction by SSE and affiliated companies to be the largest offshore site in the UK. The completion of this site will increase SSE’s renewable input to the national grid, which currently stands at 37%.

When you sign up for a renewable energy tariff you need to bear in mind that the electricity that you receive doesn’t physically change.

What you are really doing is removing your usage amount directly from unsustainable sources. By having a green tariff you are reducing the amount of non-renewable energy that suppliers need in order to fulfil their supply obligations. This, in turn, reduces their, and effectively your, carbon footprint.

Search for green tariffs

Transmission

Transmission is the stage between the energy creation source and the wooden pylon lines that are dotted around your residential localities. Transmission pylons can commonly be seen next to motorways and in open green spaces. They look a little like this:

Transmission pylons

These metal structures are used to carry extremely high voltages of electricity up and down the country at high speeds. For safety reasons they need to be large structures that allow the electricity to transported at a safe distance from the ground. The height of transmission pylons commonly ranges between 15m-55m; however, they are constructed up to 190m in the UK. There are two voltage categories for these structures: those that carry between 50,000V - 200,00V, called ‘high voltage lines’; and those that carry over 200,000V called ‘extreme high voltage lines’. Transmission lines in the UK use alternating current (AC) as their form of electricity transportation. It is vital that the network runs in such a way that allows bidirectionality in order to provide energy to where it is needed. In the USA, over the larger distances that cross state lines (etc.), high voltage direct current (HVDC) is used to efficiently transport electricity unidirectionally; however, this would not make sense in the UK because of its relatively small size and comprehensive AC network. As such, transmission lines pertain to the bidirectional AC network.

As shown in the map below, the transmission network in the UK is primarily managed by National Grid; however, in Scotland it is split into two sections: SP Energy Networks; and Scottish and Southern Energy.

Map of transmission company coverage

Maintenance

The maintenance of transmission lines and pylons is an extremely long and difficult process; however, it has the ability to add up to 50 years of life onto its functional duration. It also improves the performance of electricity transmission, allowing its transportation to be smoother and lose less energy in the process. This task is carried out by extremely skilled engineers and can take hours, days and even weeks.

Distribution

Distribution lines are local networks of small, (usually) wooden pylons that distribute lower voltage electricity over shorter distances. They look a little like this:

Distribution pylons

Because the electricity that they carry is of a considerably lesser voltage, distribution line pylons do not need to be constructed in the same manner of transmission lines. The line height of distribution pylons are not that much over 10m, which in comparison to transmission lines that in the UK have been constructed up to 190m, is rather tiny. There are two voltage categories for distribution lines: those that carry between 0V - 1000V, called ‘low voltage lines’; and those that carry between 1000V - 50,000V, called ‘medium voltage lines. The voltage that enters our homes in the UK is 230V, which means the entry point comes from the common ‘low voltage line’. Distribution lines, just like transmission lines in the UK, use AC to transport electricity to our homes. This allows networks of electricity to be much more forgiving and adaptive.

As shown in the map below each area of the UK has its own Network Distribution Operator (DNO) which manages the distribution of electricity to each household under their operation:

Distribution Network Operator map