How do we ‘pump’ electricity to where it’s needed?
Why reactive power is crucial to getting the active power we need around the country’s electricity grid.
Every time we plug in our phones to charge or turn on the kettle to make a cup of tea, the electricity we use is what’s known as ‘active power’. We tend to take it for granted. Whenever we need it, it’s always there.
But have you ever wondered how that electricity actually gets to all the places where it’s needed — like our kitchens or our offices?
That depends on something called ‘reactive power’. It’s the same as the electricity we use to charge our phones or run our kettles, but it’s used in a different way. It’s what ‘pumps’ the rest of our electricity — the active power — around the network.
The way it works is similar to a garden hose, except with small amounts of water being pumped under pressure at intervals along the length of the hose in order to keep the main flow of water going over long distances.
The trouble is each individual injection of extra pressure doesn’t go very far. So right across the UK there is a network of regional reactive power distributors who provide reactive power for their own local area. Drax power station is one of them, using some of the electricity it generates to keep the active power flowing to wherever it’s needed.
But power stations aren’t the only things that produce reactive power. Some electronic devices like laptops and TVs actually produce and feed small amounts of reactive power back into the grid. In large numbers this can lead to too much reactive power on the grid, and when this happens power stations must absorb the excess. Think, once again, of the long hose pipe — if the pressure is too great, the hose is at risk of bursting. If the pressure is too low, water won’t travel through it properly.
As our power system continues to evolve, so do our reactive power requirements. And this is partly down to the economy’s move from heavy industry to business and consumer services.
The changing needs for reactive power
“Large industrial power loads, such as those required for big motors, mills or coal mines, bring voltage down and create a demand for more reactive power,” Ian Foy, Head of Ancillary Services at Drax explains. “Now, with more consumer product usage, the demand for active power is falling and the voltage is rising.”
The result is that Drax and other power stations now spend more time absorbing reactive power rather than exporting it to keep voltage levels down. In the past, by contrast, Foy says the power plant would export reactive energy during the day and absorb it at night.
As Britain’s energy system decarbonises, the load on powerlines also becomes lighter as more and more decentralised power sources such as wind and solar are used to meet local demand, rather than large power plants supplying wider areas.
This falling load on the power system increases the voltage and creates a greater need for generators to absorb reactive power from the system to ensure we have the power we need where we need it.
Read the full story on reactive power and how it contributed to plunging New York into a blackout.
