How voltage reduction can ensure system stability

Ensuring a stable and secure electricity supply across Great Britain is one of our key roles as the organisation that operates GB’s electricity system. Our control room experts balance supply and demand every second of every day of every year, making sure you have the energy you need, when you need it.

Great Britain has one of the world’s most secure electricity systems and we work constantly in the background to make sure demand doesn’t outstrip generation.

We’re developing a way to manage this through voltage reduction, a vital tool for balancing the grid during emergencies and ensuring we maintain our world leading security of supply standards.

What is voltage?

Think of electricity like water running through your garden hose. Voltage is the push that keeps electricity moving through cables, just like water needs pressure to get from your tap to the end of your hose. Opening your tap to full allows more mass flow (more area for the same pressure to push water through), which creates high pressure and the water flows strongly to give you a powerful jet of water. Like this, high voltage enables electricity to flow strongly through cables, but it can still move without the tap being fully open i.e when voltage is reduced.

So, what is voltage control?

Voltage control allows Distribution Network Operators (DNOs), the companies that transport electricity from the high-voltage national transmission system to homes and business, to reduce the voltage running through cables, which lowers the demand of the network when there isn’t enough electricity generation on the system or in the event of anomalies like low frequency or thermal overloads.

In this instance, voltage control, is a specific action DNOs can perform in an emergency. Voltage control is also something we do constantly at NESO to manage voltage on Great Britain’s electricity system to keep it between statutory limits. Voltage must be carefully controlled because too high or too low levels can damage equipment or cause power cuts.

We manage this in real time by coordinating power stations, renewable generators, and specialised equipment on the grid. This includes instructing generators to adjust their output, switching reactive power devices like capacitors and reactors on or off, and using advanced monitoring systems to track conditions across the network.

How it works

Voltage reduction is implemented in stages, with stage one involving a 3% reduction and stage two a further 3% to a maximum total of 6%. The principle is simple: reducing voltage decreases the power consumed by devices, thereby reducing overall electricity demand.

The devices we have at home and in businesses respond differently to voltage reduction:

•    Constant Resistance Devices (e.g., kettles, old heaters): Experience a significant reduction in demand.
•    Constant Current Devices (e.g., LED lights, chargers): Show a moderate reduction.
•    Constant Power Devices (e.g., servers, precision industrial equipment): Typically, do not reduce demand.

Why don’t we run the electricity system at lower voltage all the time?

Running the network at low voltage all the time would waste a large amount of energy lost by heat and make the system inefficient. On the transmission network, electricity can travel in two ways; high voltage with low current or low voltage with high current. To constantly run the network at low voltage, we’d need more current to be generated and carried though the cables. The energy lost when it’s not being pushed through the cables at high current turns into heat in the wires, which is inefficient can put the network at risk.

We have one of the world's most secure electricity networks in Great Britain, but operating at low voltage all the time would mean redesigning pylons, substations, cables and wires, which would increase costs. Operating the system at high voltage is always going to be the most efficient way to run the transmission network, getting our electricity moving from where it’s generated to homes and businesses fast, and reducing waste.

Does it work?

To ensure we know voltage reduction can be an effective way of managing demand we conduct regular tests with DNOs. During these tests, specific DNO groups are instructed to reduce voltage by 3-6% through automated systems.

This not only tests communication between us but also validates the expected demand reduction. So far, we’ve conducted successful tests in two phases focusing on Northern and Southern blocks.

The tests have consistently shown that voltage reduction leads to a measurable demand reduction, although the extent can vary. On average, a 3% voltage reduction has resulted in approximately a 1.2% demand reduction. More detailed results and analysis from these tests are due to be shared soon and we plan to run a test involving all DNOs at the same time to refine emergency processes as well as improve the effectiveness.

Voltage reduction is more than just a technical exercise; it's a testament to the collaborative efforts of energy stakeholders to maintain a resilient and operable energy system. As technology and demand patterns evolve, continuous testing and adaptation are essential to meet future energy challenges.