Voltage Transmission lines above city.jpg
What is Voltage?
At the ESO, we move high-voltage electricity around the country using the national transmission network. But what is voltage and how does it help us keep the lights on?

Voltage is what makes electric charges move. It is the 'push' that causes charges to move in a wire or other electrical conductor.  

The ESO moves huge amounts of electricity, at a voltage of up to 400,000 volts, across the country every second of the day. That’s almost 2,000 times more than the voltage you will receive in your homes, which is typically 230 volts. So it’s a very large push indeed! 

Before electrical power leaves a power station or electricity farm, the voltage is increased using 'step-up' transformers and the current is lowered. That’s to make sure the electricity moves around in the most efficient way.  

You see, when current in a cable is high and voltage is low, energy is lost as heat. So a higher voltage and lower current means more of the energy reaches you at the other end. 

It's worth knowing that whilst it’s our job to move electricity around the system, it is National Grid Electricity Transmission who manage and maintain the transmission network - they are responsible for the infrastructure, for example the pylons and cables, needed to carry the electricity. 

Once the high voltage electricity reaches the area where it is needed, we then pass the electricity to local distribution network operators (DNOs) who reduce the voltage using ‘step-down’ transformers. The DNO’s then use their own power lines and cables to send this lower voltage electricity to your homes and businesses. 

In the same way that the ESO must maintain frequency close to 50Hz, we must keep the voltage within a safe range to ensure safety and reliability. Voltage levels across the electricity system can go up and down and may vary across different points of the electricity system. For example, at any set point in time, Northern England could experience 403,000 volts while South East England experiences 399,000 volts. 

How does the ESO manage voltage? 

To keep voltage stable, we can increase it by injecting reactive power and decrease it through absorption of reactive power. Power stations provide reactive power services when they are generating electrical power. The electricity system itself can also be used to provide reactive power; this could come from reactive equipment or from the electrical properties of cables and overhead lines. 

In the past, the ESO mainly used to take action to manage low voltage but now there are fewer industrial processes and spinning turbines we mainly manage voltage when it is higher than normal. For more information on what we’re doing to manage higher voltage in today's operating environment, check out our voltage pathfinder projects.