Tag: national grid

The silent force that moves electricity

31 August 2017

Power generation

In the early evening of 14^th August 2003, New York City, in the midst of a heatwave, lost its power. Offices, stores, transport networks, Wall Street and the UN building all found their lights and phones cut off. Gridlocked streets and a stalled subway system forced millions to commute home on foot while those unable to make it back to the suburbs set up camp around the city.

It wasn’t just the Big Apple facing blackout – what had started with several power lines in Northern Ohio brushing against an overgrown tree had spread in eight minutes to affect eight US states and two Canadian provinces. In total, more than 50 million people were impacted, $6 billion was lost in damages and 12 deaths were reported.

While a software glitch and the outdated nature of the power system contributed to the disaster, the spread from a few high-voltage power lines to the entire North West was caused by a lack of reactive power.

The pump powering electricity

Electricity that turns on light bulbs and charges phones is what’s known as ‘active power’ — usually measured in Watts (W), kilowatts (kW), megawatts (MW) or in even higher units. However, getting that active power around the energy system efficiently, economically and safely requires something called ‘reactive power’, which is used to pump active power around the grid. Reactive power is measured in mega volt amps reactive (MVAr).

It’s generated in the same way as active power by large power stations, but is fed into the system in a slightly different manner, which leads to limitations on how far it can travel. Reactive power can only be effective locally/regionally – it does not travel far. So, across the country there are regional reactive power distributors servicing each local area (imagine a long hose pipe that needs individual pumps at certain points along the way to provide the thrust necessary to transport water).

But power stations aren’t the only source of 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 increases the amount of reactive power on the grid, and when this happens power stations must absorb the excess.

This is because, although it’s essential to have reactive power on the grid, it is more important to have the right amount. Too much and power lines can become overloaded, which creates volatility on the network (such as in the New York blackout). Too little and efficiency decreases. 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.

This process of managing reactive power is, at its heart, one of ensuring active power is delivered to the places it needs to be. But it is also one of voltage control – a delicate balancing act that, if not closely monitored, can lead to serious problems.

Keeping volatility at bay

Across Britain, all electricity on the national grid must run at the same voltage (either 400kV or 275kV – it is ‘stepped down’ from 132kV to 230V when delivered to homes by regional distribution networks). A deviation as small as 5% above or below can lead to equipment being damaged or large scale blackouts. National Grid monitors and manages the nationwide voltage level to ensure it remains within the safe limit, and doing this relies on managing reactive power.

Ian Foy, Head of Ancillary Services at Drax explains: “When cables are ‘lightly loaded’ [with a low level of power running through them], such as overnight when electricity demand is lower, they start emitting reactive power, causing the voltage to rise.”

To counter this, generators such as Drax Power Station, under instruction from National Grid, can change the conditions in their transformers from exporting to absorbing reactive power in just two minutes.

This relies on 24-hour coordination across the national grid, but 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,” explains Foy. “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. It highlights that while Drax’s role in balancing reactive power has changed, it remains an essential service.

This short story is adapted from a series on the lesser-known electricity markets within the areas of balancing services, system support services and ancillary services. Read more about black start, system inertia, frequency response and reserve power. View a summary at The great balancing act: what it takes to keep the power grid stable and find out what lies ahead by reading Balancing for the renewable future and Maintaining electricity grid stability during rapid decarbonisation .

Why we need the whole country on the same frequency

23 June 2017

Power generation

The modern world sits on a volatile, fizzing web of electricity. In 2015 the UK consumed roughly 303 terawatt hours (TWh) of electricity, according to government statistics. That’s an awful lot of power humming around and, in this country, we take it for granted that electricity is controlled. This means the power supply coming into your home or place of work is reliable and won’t trip your fuse box. In short, it means your mobile phone will keep on charging and your washing machine will keep on spinning.

But generating and circulating electricity at safe, usable levels is not an easy task. One of the most overlooked aspects of doing this is electrical frequency – and how it’s regulated.

What is electrical frequency?

To understand the importance of frequency, we need to understand a couple of important things about power generation. Generators work by converting the kinetic energy of a spinning turbine into electrical energy. In a steam-driven generator (like those at Drax Power Station), high pressure steam turns a turbine, which turns a rotor mounted inside a stator. Copper wire is wound around the rotor energised with electricity, this turns it into an electromagnet with a north and south pole.

The stator is made up of large, heavy duty copper bars which enclose the rotor. As the rotor turns, its magnetic field passes through the copper bars and induces an electric current which is sent out onto the transmission system.

As the magnetic field has a north and south pole, the copper bars experience a change in direction of the magnetic field each time the rotor turns. This makes the electric current change direction twice per revolution and is called an alternating current (AC). There are in fact three sets of copper bars in the stator, producing three electrical outputs or phases termed red, yellow and blue.

Electrical frequency is the measure of the rate of that oscillation and is measured in the number of changes per second – also called hertz (Hz). A generator running at 3,000 rpm, with two magnetic poles, produces electricity at a frequency of 50Hz.

Why is this important?

Maintaining a consistent electrical frequency is important because multiple frequencies cannot operate alongside each other without damaging equipment. This has serious implications when providing electricity at a national scale.

The exact figure is less important than the need to keep frequency stable across all connected systems. In Great Britain, the grid frequency is 50Hz. In the US, it’s 60Hz. In Japan, the western half of the country runs at 60Hz, and the eastern half of the country runs at 50Hz – a string of power stations across the middle of the country steps up and down the frequency of the electricity as it flows between the two grids.

Sticking to one national frequency is a team effort. Every generator in England, Scotland and Wales connected to the high voltage transmission system is synchronised to every other generator.

When the output of any of the three phases – the red, yellow or blue – is at a peak, the output from all other phases of the same colour on every other generating unit in Great Britain is also at a peak. They are all locked together – synchronised – to form a single homogenous supply which provides stability and guaranteed quality.

How is frequency managed?

The problem is, frequency can be difficult to control – if the exact amount of electricity being used is not matched by generation it can affect the frequency of the electricity on the grid.

For example, if there’s more demand for electricity than there is supply, frequency will fall. If there is too much supply, frequency will rise. To make matters more delicate, there’s a very slim margin of error. In Great Britain, anything just 1% above or below the standard 50Hz risks damaging equipment and infrastructure. (See how far the country’s frequency is currently deviating from 50 Hz.)

Managing electrical frequency falls to a country’s high voltage transmission system operator (the National Grid in the UK). The Grid can instruct power generators like Drax to make their generating units automatically respond to changes in frequency. If the frequency rises, the turbine reduces its steam flow. If it falls it will increase, changing the electrical output – a change that needs to happen in seconds.

In the case of generating units at Drax Power Station, the response starts less than a second from the initial frequency deviation. The inertial forces in a spinning generator help slow the rate of frequency change, acting like dampers on car suspension, which minimises large frequency swings.

Frequency on a fast-changing system

Not all power generation technologies are suited for providing high quality frequency response roles and as the UK transitions to a lower-carbon economy, ancillary services such as stabilisation of frequency are becoming more important.

Neither solar nor wind can be as easily controlled. It’s possible to regulate wind output down or hold back wind turbines to enable upward frequency response when there is sufficient wind.

Similarly, solar panels can be switched on and off to simulate frequency response. As solar farms are so widely dispersed and tend to be embedded – meaning they operate outside of the national system, it is not as easy for National Grid to instruct and monitor them. Both wind and solar have no inertia so the all-important damping effect is missing too. Using these intermittent or weather-dependent power generation technologies to help manage frequency can be expensive compared to thermal power stations.

Nor are the current fleet of nuclear reactors flexible – nuclear reactors in Great Britain were designed to run continuously at high loads (known as a baseload power). Although they cannot deliver frequency response services, the country’s nuclear power stations do provide inertia.

Twenty times faster

Thermal power generation technologies such as renewable biomass or fossil fuels such as coal and gas are ideal for frequency response services at scale, because they can be easily dialled up or down. As both the fuel supply to their boilers and steam within their turbines can be regulated, the 645 MW thermal power units at Drax have the capability to respond to the grid’s needs in as little as half a second or less, complete their change in output in under one second and maintain their response for many minutes or even hours.

Before the introduction of high volumes of wind and solar generation almost all generators (excluding nuclear) running on the system could provide frequency response. As these generators are increasingly replaced by intermittent technologies, the system operator must look for new services to maintain system stability.

An example is National Grid’s recent Enhanced Frequency Response tender, which asked for a solution that can deliver frequency stabilisation in under a second – 20 times faster than the Primary Response provided by existing thermal power stations. Drax was the only participating thermal power station, however all contracts were all won by battery storage projects.

Frequency future

Given the decline in fossil fuel generation and uncertainty around our power makeup in future decades, National Grid is consulting on how best to source services such as frequency response. The ideal scenario for National Grid is one where services can be increasingly sourced from reliable, flexible and affordable forms of low carbon generation or demand response.

The next generation of nuclear power stations, as with some already operating in France, can provide frequency response services. However the first of the new crop, Hinkley C, is around a decade away from being operational. Likewise, solar or wind coupled with battery, molten salt or flywheel storage will provide an increasing level of flexibility in the decades ahead as storage costs come down.

Thanks to power generation at Drax with compressed wood pellets, a form of sustainable biomass, Britain has already begun moving into an era where lower carbon frequency response can begin to form the foundation of a more reliable and cleaner system.

This story is part of a series on the lesser-known electricity markets within the areas of balancing services, system support services and ancillary services. Read more about black start, system inertia, reserve power and reactive power. View a summary at The great balancing act: what it takes to keep the power grid stable and find out what lies ahead by reading Balancing for the renewable future and Maintaining electricity grid stability during rapid decarbonisation .

Your neighbourhood electricity network

31 January 2017

Electrification

Engineers from Electricity North West fixing electricity wires.

Britain’s electricity network is a lot like its roads. For long distance, high-speed journeys, the road network has motorways – the electricity network’s equivalent is the National Grid, which transfers power across the country at extremely high voltages (between 400,000-132,000 volts) and high speeds.

For shorter journeys at progressively lower speeds, the traffic network has ‘A’ and ‘B’ roads. These are the regional distribution networks.

These regional distribution networks take power at 132,000 volts and transform it down in stages to 230 volts and make the link from the National Grid to local distribution systems that deliver electricity to homes and businesses.

And while these A and B roads of electricity may be one of the most important parts of getting electricity from power station to plug, very few people spare them any thought.

Electricity in the north west

“When the government first privatised the electricity network in 1989, it set up different distribution regions to provide national coverage through a series of similarly-sized regions,” says Pete Emery, Senior Director of Electricity North West.

Today each part of the UK is served by one of 14 different regional networks and in the north west, across the Pennines from where Drax Power Station operates in North Yorkshire, that’s the job of Electricity North West. It was formed in 1995 and today delivers around 23 terawatts of power to 2.2 million homes and 200,000 business every year.

It does that using a vast network of more than 13,000 km of overhead cables, 44,000 km of underground cables (making it the second most underground electricity network in the UK behind London) and more than 34,000 transformers, which work to convert the electricity from transmission voltage to one that can be used in UK homes.

The scale of infrastructure needed to create these regional networks mean that each one is a ‘natural monopoly’. In this case, it’s a monopoly that benefits customers.

A ‘natural monopoly’

“A natural monopoly is when the cost of duplicating the assets needed to provide the service outweighs the benefits of efficiency that having competition would provide,” explains Emery. “So it is in the public interest to have only one provider.”

For decades, each regional distribution network has operated the same way, delivering power consistently to UK homes. But as the country moves into the future of cleaner, more sustainable energy, these grids are changing rapidly.

The potential proliferation of battery technologies, and the increasing variation of power sources and their demands on the grid mean changes are in store for distributors like Electricity North West.

One such factor already having an effect is embedded generation. Across the country there are sources of electricity generation that aren’t connected to regional distribution networks – for example, private solar panels on domestic roofs, wind turbines on private land, or small-scale power stations connected to a single, private distribution network. And when there is excess electricity generated from these sources, it can be sold back to electricity suppliers. In the north west, this embedded generation is fed back into Emery’s network.

“In our region alone, we have 2,200 MW of embedded generation – more than half the capacity of Drax Power Station – which means we already manage and control the power this input brings to the electricity system,” says Emery. “They are invisible to National Grid. This is a radical change and it’s happening now.”

Regardless of what’s to come, what’s certain is there’ll be traffic on the A roads of electricity.

These three inches of copper can power a city

17 January 2017

Electrification

A series of unassuming cables extend out of the turbine hall at Drax Power Station. They’re easily missed, but these few inches of copper play an instrumental role in powering your home. Surging through each one is enough electricity to power a city.

But the process of getting electricity from power station to plug isn’t as simple as connecting one wire to a live turbine and another to your iPhone charger. We need an entire network of power stations, cables and transformers.

Linking the network

When the country first became electrified it did so in stages. Each region of the UK was powered by its own self-contained power supply. That changed in 1926 when the UK set up the Central Electricity Board and began what was at the time the biggest construction project Britain had ever seen: the national grid

The project took 100,000 men and five years to complete and when it was finished it connected 122 of the country’s most efficient power stations via 4,000 miles of overhead cabling. It had a sizeable effect. In 1920 there were roughly 750,000 electricity consumers; by 1938 that had risen to 9 million.

The grid has changed in the 80 years that’s passed, but it remains the network that transfers power across the country to where it’s needed, whenever it’s needed.

“The strange thing about electricity is that you could live 10 miles from a power station and you can’t be sure the electricity you’re using is coming from that station,” says Callan Masters, an engineer with National Grid whose job it is to maintain and upgrade the network. “The whole system works together – the whole system has a demand and the whole system has to deliver it.”

And to do this, the network has to be able to deliver electricity quickly and efficiently. Masters explains: “It acts like a motorway for power.”

Riding the motorway for power

The process of transporting electricity involves a series of stages, the first of which is ‘stepping up’ the voltage.

When electricity is transported via cables or wires it loses some of its energy as heat. Think of a lightbulb – as it illuminates it heats up because it’s losing energy. The lower the current of that electricity, however, the less energy is lost. So to reduce these losses when transporting power, National Grid transmits electricity at low currents, which it can do by increasing its voltage.

At the power station electricity is generated at 23,500 volts and is then ‘stepped up’ to 400,000 volts by a transformer. The first of these is located on a substation on site at the power station.

Once stepped up, the electricity is transported through high transmission cables – before being ‘stepped down’ via a transformer on the other end. This stepped down electricity is passed onto a regional distribution system, such as the overhead cables you might find on top of wooden poles before being stepped down a final time. “That’s the role of a little transformer at the end of your street,” Masters explains. Finally, the electricity is transported via a final cable into your home – this time at 230 volts.

All this needs to happen incredibly quickly. As thousands of kettles are switched on to herald the end of EastEnders, the demand of electricity surges. Delivering that electricity at the touch of a button relies on a complex network, but it starts with those inconspicuous few inches of copper at the power station.

Your Christmas lights were powered by more renewables than ever before

29 December 2016

Electrification

A single strand of Icicle Christmas Lights.

Late into the evening of Christmas Day, 2016, millions of people sat down to watch Rowan Atkinson solve a grisly murder. It was the TV drama Maigret’s Dead Man, and although it wasn’t the most watched TV show on Christmas Day (that honour went to the Strictly Come Dancing finale), it did cause the biggest television-related sudden surge in electricity demand of the day, says Sumit Gumber, Energy Forecasting Analyst at National Grid.

During a critical ad break in the show, demand jumped 400 MW – roughly equivalent to 160,000 kettles being switched on – as viewers raced to make cups of tea or go to the bathroom. This is known as a TV pickup.

While this may have provided the biggest sudden rise in electricity usage of the day, it was not the overall peak. As is typical on Christmas Day, this year’s spike in demand came just before one o’clock, when families were preparing their festive feasts.

At 37.1 GW, this peak was not only lower than previous years, the power used to supply it was generated by more renewables than any Christmas before it. More than 40% of the electricity generated on Christmas Day came from renewable sources.

What characterises Christmas day?

Christmas is a day when electricity usage is at one of its lowest points. To put this year’s 37.1 GW peak into context, an average weekday during December (weekday electricity use is higher than on weekends) has an electricity peak of nearly 50 GW, usually occurring between five and seven o’clock, when people arrive home and street lighting is switched on.

The cause for the lower demand during Christmas is simple – over the festive period schools, as well as a number of offices, shops and factories are closed.

Over the last few years average Christmas Day demand has been fairly typical, sitting in a bracket of between 29 GW and 39 GW. In 2010, however, extreme cold (hitting minus three degrees Celsius) drove lunchtime peak demand as high as 46 GW, showing just how important a driver of our electricity use temperature is.

But while demand on Christmas in 2016 may not have deviated largely from the average over the last few years, there were some major leaps forward in how it was generated.

A greener Christmas than ever before

This year, Christmas was characterised by a huge jump in renewable electricity generation. On average, 12.4 GW came from renewable sources – more than ever before. Of that figure, wind contributed the most, generating on average 9.4 GW – equivalent to 31% of all power supplied on Christmas Day.

Compared to 2015 it’s a 63% increase and a staggering 195% uplift from five Christmases ago in 2012 when just 12% of all electricity generated came from renewable sources. Biomass generation has also increased, providing 2 GW in 2016 compared to the 0.5 GW it averaged on December 25^th, 2012.

The increase in renewables also marks an important step towards decarbonisation: at its peak, emissions from electricity generation this 25^th December were just 168 g/kWh, a significant drop compared to the 2012 peak of 506 g/kWh and the 303 g/kWh seen in 2015.

This year has been a year of impressive stats in clean energy: between July and September, for the first time in its 130-year-old history, more than half of Britain’s power came from low-carbon sources; on 5^th May the UK did not burn any coal to generate electricity, the first time since 1881. Now, we’ve seen one of the cleanest Christmases on record. It’s a Christmas tradition that is likely to continue.

Biggest TV pick-ups, Christmas Day 2016

Maigret’s Dead Man and EastEnders (22:30) – 400 MW (equivalent to 160,000 2.5 kW kettles switched on)
Paul O’Grady: For the Love of Dogs at Christmas (19:45) – 275 MW (110,000 kettles)
The Great Christmas Bake Off (17:45) – 210 MW (84,000 kettles)
Emmerdale and Doctor Who (18:45) – 200 MW (80,000 kettles)

_{Thanks to National Grid for this data}

Explore how Britain was powered over the festive period by visiting electricinsights.co.uk.

Power and the rise of electric cars

12 December 2016

Electrification

Power supply for electric car charging. Electric car charging station. Close up of the power supply plugged into an electric car being charged.

All great technological innovations need infrastructure to match. The world didn’t change from candles to lightbulbs overnight – power stations had to be built, electricity cables rolled out, and buildings fitted with wiring. The same is true of electric vehicles (EV).

Think of the number of petrol stations lining the UK roads. If EVs continue their rise in popularity, the country will need electric car-charging facilities to augment and then replace these petrol stations.

This could mean big extensions of electricity grid infrastructure, both in the building of new power generation capacity to meet demand, and in the extension of the networks themselves.

In short, it could mean a significant change in how electricity is used and supplied.

The need for better electricity infrastructure

In 2013, only 3,500 of newly registered cars in the UK were plug-in electric or hybrid EVs. In 2016, that number jumped to 63,000. Their use is rising rapidly, but the lack of infrastructure has kept a cap on the number of EVs on UK roads. That is starting to change.

As of 2019, all new and refurbished houses in the EU will have to be fitted with an electric car charging point, according to a draft directive announced by Brussels. The UK will probably no longer be an EU member by the time the directive comes into effect, but nevertheless, the UK government is pursuing its own ways to account for the rise of EVs. It has pledged more than £600 million between 2015 and 2020 to support ultra-low-emission vehicles – £38 million of this has already been earmarked for public charging points.

There are more innovative responses to EV rise, too. Nissan, in partnership with Italian energy provider Enel, has announced it will install around one hundred ‘car-to-grid’ charging points across the UK. With their innovative V2G technology, cars plugged into these sites will be able to both charge their batteries and feed stored energy back to the National Grid when necessary. So when there is a peak in demand, the Grid could access the cars’ stored energy to help meet it.

The total capacity of the 18,000 Nissan electric vehicles currently operational on UK roads comes to around 180 MW. So even today – before electric vehicles have really taken off – this could give the National Grid an additional supply roughly the size of a small power station.

Peaks in electricity demand, however, tend to occur in the late afternoon or evening as it gets dark and more lighting and heating gets switched on. This also happens to be rush hour, so under this scheme the time of day the cars are most likely to be on the roads is also when it’d be most helpful to have them plugged in. This could lead to financial incentives for people to give up the flexibility of driving their cars only when they need to.

More electric cars, more demand for electricity, more pollution?

More EVs on the road makes sound environmental sense – they enable a 40% reduction in CO2 emissions – but ultimately the energy still has to come from somewhere. That means more power stations.

The scale of this new demand shouldn’t be underestimated: if European drivers were to go 80% electric, some studies have suggested it would require 150 GW of additional on-demand capacity – the equivalent of 40 Drax-sized power stations.

But if EVs are to live up to their green potential, that additional power needs to come from innovations in storage (such as in the Nissan example) and from renewable sources like wind, solar and biomass. Fossil fuels would ideally be used only to plug any gaps that intermittency creates – for example by briefly firing up the small gas power stations Drax plans to build in England and Wales.

What does this mean for generators?

Drax, as operator of the UK’s largest biomass power station and with plans for new, rapid response open cycle gas turbines (OCGTs), is well placed to be at the forefront of providing reliable, affordable power in the event of a widespread rollout of electric vehicles. The OCGTs in particular, are designed for use in peak times which, in the future, could be when the nation’s electric vehicles are plugged in overnight – today this is when electricity demand is at its lowest.

A future of more electric cars is a positive one. They’re cleaner, more efficient, and they are well suited to our increasingly urban lives. But now that we have the technology, we need to ensure we can deliver the lower-carbon infrastructure they need.

Tag: national grid