What is Frequency?
At the ESO, we monitor frequency second by second to make sure that your appliances and equipment continue to work as they should. But what actually is frequency and why is it so important?

Frequency literally means the number of times something happens over a period of time.  

When you turn on an appliance, for example your kettle or laptop charger, it uses alternating current to power it. This means that the current is alternating between a positive and negative voltage.   

This backwards-and-forwards motion or “oscillation” is known as electrical frequency. In the UK, alternating current oscillates 50 times every second, meaning our frequency is 50 hertz (50Hz).  

All UK appliances and electrical equipment are designed to work at 50Hz. If the frequency is not 50Hz then these appliances won’t work – the tolerance is very small, meaning that we have to keep the frequency within a tight window either side of 50Hz. 

It’s therefore important to constantly monitor frequency right across GB’s electricity network to make sure it stays close to 50hz every second. 

As supply and demand change, this impacts frequency. For example, if there’s more demand for electricity than supply then frequency will fall, but if supply is higher than demand, frequency will rise. 

We’re required to routinely keep the frequency within one percent (0.5Hz) of 50Hz, but in aiming to meet that requirement we set ourselves a tighter operational target than required, and aim to maintain frequency within 0.2Hz of 50Hz in normal conditions. 

It is our job at the ESO to manage frequency in our control room, balancing supply and demand every second of every day to make sure that the frequency stays where it should be. One of our control room experts constantly monitors the frequency – this is such an intense job that they can only do this for an hour at a time before swapping with another member of the team.  

Find out more about how we balance the grid. 

As demand rises, we ask providers to turn up their energy sources to balance the system and keep frequency close to 50hz. Equally, when demand drops, we might as an operator ask them to reduce generation to avoid frequency being too high. Our control room uses tools like the balancing mechanism to do this. 

Britain’s power grid is a complex, live system, so things do occasionally break – whether it be a fault on a power line or a generator having issues. These faults can cause a big change in supply or demand on the network which can cause rapid changes in the frequency.  

We at the ESO prepare for these events and ensure that we have enough services available to counteract the fault and restore the frequency quickly. In 2020 we launched one of the fastest services in the world – Dynamic Containment – which is able to respond within half a second to any changes in the frequency. 

Since we’ve been running more zero carbon energy sources on our system, we’ve changed the way we manage frequency. As we move away from traditional large thermal power generation to cleaner, more decentralised power, the system reacts more rapidly to changes in supply and demand. 

Services like Dynamic Containment and our Accelerated Loss of Mains Change programme – which is changing smaller generators’ settings to reduce the risk of them tripping when the frequency changes – are making the system more secure as it becomes greener.  

Find out more about zero carbon here. 

At the ESO we’re on track to run the grid on zero carbon electricity by 2025. To help us achieve this, we have a portfolio of active innovation projects and we’re aiming to undertake large, collaborative, whole system projects using Ofgem’s new Strategic Innovation Fund (SIF). 

You can find out more about our projects here.