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Why is Grid frequency important in keeping your business power on?

31st October 2019

When a major power outage caused chaos across parts of the UK in August, suspicion fell on a sudden decrease in frequency on the grid. But what is frequency, why does it matter for your business, and how can the industry maintain it as the UK moves to an increasingly distributed grid?

According to the interim report from the Office of Gas and Electricity Markets (Ofgem) about events on 9 August, lightning struck a power cable north of London at 4.52pm. Although normal service was resumed in seconds, around 500MW of embedded generation connected to the distribution network (rather than the transmission network) was lost. Moments later, Little Barford Power Station went offline unexpectedly – followed, minutes later, by an offshore wind farm at Hornsea.

Suddenly, the grid was short (by just under 1.7GW) of the power it needed to meet demand – causing frequency to drop from its normal level of 50Hz to below 48.9Hz. As a result, the system automatically disconnected some electricity demand to prevent any further fall in frequency.

Many businesses suffered huge disruption, as did organisations providing essential services. For example, Newcastle Airport was blacked out, Ipswich Hospital lost power, and parts of the rail network in south-east England were plunged into chaos.

What is frequency (and why is it so important?)

The electricity that drives the electrical equipment in your business is called alternating current (AC). This alternation occurs when turbines that rotate an electromagnet inside an array of large copper bars generate electricity thermally. The electromagnet has a north and a south pole, so on every turn, it alternates between a positive and negative voltage in what’s known as a sinusoidal rotation.

The rate of this alternation is called electrical frequency; the AC voltage generated in the UK alternates 50 cycles a second – giving it a frequency of 50 Hertz (Hz).

Almost all of the electrical equipment in your business runs at 240 volts AC (VAC) with a frequency of 50Hz. So, generators across the UK are synchronised to transmit electrical power to the high voltage transmission system at a frequency of 50Hz. (You can find the precise current frequency of the grid here).

The rise and fall of demand for electricity can have a big effect on frequency. If electricity generation outweighs demand, the electrical frequency increases; if there’s more demand than electricity being produced, the frequency falls.

And, if the frequency rises or falls too far beyond the standard 50Hz, there can be very serious consequences – as happened on 9 August.

How is frequency managed?

In the UK, National Grid Electricity System Operator (ESO) is ultimately responsible for keeping the grid’s frequency stable. ESO pays generators – including Haven Power’s parent company, Drax – to provide something called ‘frequency response’ services. This ensures that ESO can rectify frequency variations very quickly – for example, Drax has set its generators to automatically respond in less than a second.

Such speed of response is much easier to achieve with thermal generation than it is with power generated via solar panels or wind turbines. That’s because you can run thermal generators faster or slower to change the frequency of the electricity they produce. However, you can’t do this with solar or wind generation; it’s possible to increase or decrease how much power they produce, but impossible to adjust their frequency output.

Today, solar farms generally deliver what’s known as distributed electricity (i.e. not generated for transmission via National Grid) that’s for local consumption. This further limits the extent to which solar can help to balance the network.

Before distributed power emerged as an option for generation, almost all electricity was generated thermally then shared around the country through the high voltage transmission network. This meant that National Grid could call upon most power stations to help balance the frequency.

Now, with the amount of ‘distributed’ wind and solar power growing, ancillary services – such as the frequency response that Drax and others provide – will become more important. And, in turn, these services will become even more vital in helping to keep your business going 24/7.

To find out how Haven Power can help your business with its energy, please get in touch by using our contact form.

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