Electrical substations play a key part in effectively transmitting electricity through our national system. Find out what they do, how they work and where they fit into our electricity grid.
There’s more to our electricity system than where power is generated, or the cables that brings it to our homes and businesses. In fact, the national electricity grid comprises an ingenious network of specialist equipment that allows for the safe and effective transmission and distribution of electricity.
Substations are integral features within that grid and enable electricity to be transmitted at different voltages, safely and effectively.
One of the main roles of substations is to convert electricity into different voltages. This is needed so the electricity can be transmitted throughout the country and into our homes, businesses and buildings.
Substations contain the specialist equipment that allows the voltage of electricity to be transformed (or ‘switched’). The voltage is stepped up or down through pieces of equipment called transformers, which sit within a substation’s site.
Transformers are electrical devices that transfer electrical energy by means of a changing magnetic field. They consist of two or more coils of wire and the difference in how many times each coil wraps around its metallic core will affect the change in voltage. This allows for the voltage to be increased or decreased.
Substation transformers will fulfil different purposes in voltage conversion, depending on where electricity is in its transmission journey.
The two most common types of substations are transmission substations and distribution substations.
Transmission substations are found where electricity enters the power grid. Because the output from power generators – such as power stations or wind farms – varies in voltage (between 130 kilovolt (kV) and 400kV in the UK, and up to 600kV in the US) it must be converted to a level that suits its means of transmission.
Electricity is then commonly transmitted through the high-voltage, overhead power lines you see supported by electricity pylons and can travel vast distances. In the UK, these run at either 275kV or 400kV. Increasing or decreasing the voltage to suit will ensure that it reaches local distribution networks safely and without significant energy loss.
The electricity is then routed from the transmission system into a distribution substation, which will lower the voltage – to around 11kV in the UK – so it can enter our homes and businesses at a usable level. This is carried through a distribution network of smaller overhead lines or underground cables into buildings at 240V.
Substations contain equipment that help keep our electricity transmission and distribution systems running as smoothly as possible, without repeated failure or downtime.
Specialist equipment within the substation site can help prevent local network failures or power cuts. This happens when there is an overload of current in the network, which can be caused by things like mechanical failure or adverse weather conditions.
National Grid owns more than 300 large substations, where 275kV and 400kV overhead power lines or underground cables are switched and where electricity is transformed for distribution to surrounding areas.
Smaller substations are owned and maintained by local distribution networks, including our Electricity Distribution business (formerly Western Power Distribution).
In past years there has been some debate about whether living next to substations – and indeed power lines – is safe, because of the electromagnetic fields (EMFs) they produce.
Such concerns are taken seriously and it's our priority to keep the public, our contractors and employees safe. All substations are designed to produce EMFs below independent safety guidelines, set to protect us all against exposure. After decades of research, the weight of evidence is against there being any health risks of EMFs below the guideline limits.
However, a substation can pose a very real risk of electrocution, serious injury or death if the equipment is interfered with. Under no circumstance should members of the public enter a substation site or touch any of the equipment inside them.
All substations are fenced off from the general public and feature yellow and black triangular signs that carry electrocution warnings.
Last updated: 22 Aug 2022
The information in this article is intended as a factual explainer and does not necessarily reflect National Grid's strategic direction or current business activities.