Tag: technology

How turbines came to power the world

Charles Algernon Parsons knew he was onto something in 1884. The young engineer had joined a ship engineering firm and developed a steam turbine engine, which he immediately saw had a bigger potential than powering boats.

He connected it to a dynamo, turning it into a generator capable of producing up to 7.5 kilowatts (kW) of power, and in the process kickstarted an electrical and mechanical revolution that would reshape how electricity was produced and how the world worked.

Today turbine-based generation is the dominant method for electricity production throughout the world and even now – almost a century and a half later – Parsons’ turbine concept remains largely unchanged, even if the world around it has.

Steam dreams

Throughout the 20th and into the current century, electricity generation has depended on steam power. Be it in a coal, nuclear or biomass power plant, heating water into highly pressurised steam is at the core of production.

Greek mathematician and inventor Hero of Alexandria is cited as building the first ever steam engine of sorts with his aeolipile, which used steam to spin a hollow metal sphere. But it wasn’t until the 18th century, when English ironmonger Thomas Newcomen designed an – albeit inefficient – engine to pump water out of flooded mines, that steam became a credible power in industry.

Scottish engineer James Watt, from whose name the unit of energy comes from, built on these humble beginnings and turned steam into the power behind the industrial revolution around 1764 when he added an condensing chamber to Newcomen’s original design.

It was the combination of this engine with Thomas Edison’s electrical generator late in the 19th century that first made large-scale electricity production from steam a reality.

The turbine takes over

Steam engines and steam power was not a new concept when Parson began his explorations in the space. In fact, nor were steam turbines. Others had explored ways to use stream’s velocity to spin blades rather than using its pressure to pump pistons, in turn allowing rotors to spin at much greater speeds while requiring less raw fuel.

What made Parsons’ design so important was its ability to keep rotational speeds moderate while also extracting as much kinetic energy from steam jets as possible.

He explained in a 1911 Rede Lecture that this was done by “splitting up the fall in pressure of the steam into small fractional expansions over a large number of turbines in series,” which ensured there was no one place the velocity of the blades was too great.

The design’s strength was also apparent at scale. In 1900 his company (which was eventually acquired by Siemens) was building turbine-generator units capable of producing 1,000 kW of electricity. By 1912, however, the company was installing a 25,000 kW unit for the City of Chicago. Parsons would live to see units reach 50,000 kW and become the primary source of electricity generation around the world.

Turbines in the modern grid

The world is a vastly different place to the one in which Parson designed his turbine, yet the fundamentals of his concept have changed very little. The results of what they achieve and the scales at which they work, however, have increased significantly.

Today the turbines that make up Drax’s six generating units are each capable of producing more than 600 MW (or 6,000,000 kW) of electricity with the shape, materials and arrangement of blades carefully designed to maximise efficiency.

And while that first design was purely with steam in mind, turbine technology has advanced beyond dependency on a single power source, and has been developed to accommodate for the shift towards lower-carbon power sources.

One such example is gas turbines, which work by sucking in air through a compressor, which is then heated by burning natural gas, in turn spinning a turbine as it expands. These can jump into action much faster than other turbines as they don’t require any steam to be created to power them.

Renewable sources, such as hydro and wind power, also depend on spinning turbines to generate electricity. Where these differ from gas or steam-powered turbines is that rather than being encased in metal and blasted with gases, wind and hydro turbines’ blades are exposed, so flowing air or water can spin them, powering a generator in turn.

Turbine technology helped bring access to electricity around the world, but the ingenuity and flexibility of the design means it is now serving to adapt electricity production for the post-coal age.

The everyday and future ways you use forest products

Think of the products that come from forests and you might think of the centuries of shipbuilding, construction and cooking made possible by civilisations utilising this plentiful natural resource.

What you might not think of is the complex construction of chemicals and matter that make up the trees of a forest – nor of the countless ways these can be broken down and used. Yet this is the reality of forests. From essential oils to sturdy packaging to powerful adhesives, trees are used to create a range of products that make daily life possible.

And as awareness of the need to reduce plastic consumption grows, research into forest products and how they can replace the less-environmentally friendly objects is growing.

Here we look at five of the most common products used today, and maybe in the future, that owe something to forests.

Adhesives from tall oil

Anyone who has encountered tree sap can attest: trees are made up of some pretty sticky stuff. And it’s because of this that they have long been a source for adhesives production – from glue to cement.

The substance that makes this possible is known as tall oil. Named after the Swedish word Tallolja, meaning pine oil, it is a by-product of pulping coniferous trees.

Tall oil has been produced commercially since the 1930s when the invention of the recovery boiler made it possible to extract it from the Kraft pulping process. However, the resins and waxes tall oil is made up of have a longer history. These are also known as ‘Naval Products’ due to their historic use in ship building and can be tapped directly from living trees.

Today, tall oil is also used in asphalt roofing, as well as medical and cosmetic applications. One of tall oil’s most exciting uses is as BioVerno – a renewable alternative to diesel made in the world’s first commercial-scale biorefinery in Finland.

Disinfectants and detergents from turpentine

Tapping trees has historically been a means of extracting multiple useful substances and one of the most versatile of these is turpentine. This yellowish liquid is produced from distilled tree resin and has a long history of uses.

Turpentine has been used since Roman times as torch or lamp fuel, but its antiseptic properties also means it was often used as medicine. While doctors today would advise against drinking turpentine (as was prescribed in the past), it is still used today in disinfectants, detergents and cleaning products, giving off a fresh, pine-like odour.

Fuels to replace fossils

Biomass pellets from working forests are just one of the ways trees are providing renewable energy. One other form is cellulosic ethanol, a new, second generation of liquid biofuel. Rather than competing with food supply (often a concern in the creation of biodiesels), cellulosic ethanol is made from non-food based materials such as forest and agricultural residues left behind after harvest – wheat straw, – and timber processing wastes including sawdust. It is now being produced at a commercial scale in Europe, the US and Brazil.

Woody biomass can also be converted into a petroleum substitute known as pyrolysis oil or bio-oil. Biomass is transformed into this dark brown liquid by heating it to 500oC in an oxygen-deprived environment and then allowing it to cool. Bio-oil has a much higher energy density than biomass in chip or pellet form and after upgrading can be used as jet fuel or as a petroleum alternative in chemical manufacturing.

Vanilla ice cream and carbon fibre from lignin

Lignin is what gives trees their tough, woody quality, and after cellulose is the world’s second most abundant natural polymer. Polymers are very long molecules made up of many smaller molecules joined end-to-end most often associated with plastic, (which is a synthetic polymer).

Lignin is generally a waste product from the paper pulping process and is often burnt as fuel. However, it can also serve as a vanilla flavouring – a property that may make lignin an important resource in the face of an impending vanilla pod shortage.

Future-looking research, however, aims to unlock much more from the 50 million tonnes of lignin produced every year globally. One of the most promising of these is as an alternative source of a family of organic compound known as phenylpropanoids. These are normally extracted from petroleum and are hugely useful in producing plastics and carbon fibre, as well as drugs and paint. 

Nanocellulose and the future of forest products

Cellulose is already one of the most important products to come from forests thanks to its role in paper production. However, this abundant substance – which is also the primary material in the cell walls of all green plants – holds even more potential.

By shrinking cellulose down to a nano level it can be configured to be very strong while remaining very light. This opens it up as a product with many possibilities, including using it as a source of bioplastics. Some bioplastics – polylactic acid, PHA, PBS and starch blends – are biodegradable alternatives to fossil fuel-based plastics and could potentially help solve some of the world’s most-pressing waste issues.

Not all bio-based plastics are biodegradable, however. The property of biodegradation doesn’t depend on the resource basis of a material – it is linked to its chemical structure. In other words, 100% bio-based plastics may be non-biodegradable, and 100% fossil-based plastics can biodegrade.

Bio-based plastics that are not biodegradable include polyethylene terephthalate, polyurethanes, polyamide, polyethylene. Polyethylenefuranoate or PEF is recyclable, can be manufactured without fossil fuels and while not biodegradable, has the potential to become a more sustainable alternative to the oil-based plastic used to make water bottles.

Cellulose’s combination of strength and light weight has also attracted interest from the auto industry in the ability to help cars become much lighter and therefore more fuel efficient. Its flexible, strong, transparent nature can also make Nanocellulose – an important material in helping bring bendable screens, batteries, cosmetics, paper, pharmaceuticals, optical sensors and devices to market.

The idea of using trees as a source of goods and products in everyday life might sound archaic, but, in reality, we’ve only just tapped the surface of what the chemicals and materials they’re made of can do. Markus Mannström from Finnish renewables company Stora Enso said recently that: “We believe that everything made from fossil-based materials today, can be made from a tree tomorrow.” As research advances, trees and forests will only play a bigger role in a more sustainable future.

How to switch a power station off coal

Turbine hall at Drax Power Station

In 2003, the UK’s biggest coal power station took its first steps away from the fossil fuel which defined electricity generation for more than a century. It was in that year that Drax Power Station began co-firing biomass as a renewable alternative to coal.

It symbolised the beginnings of the power station’s ambitious transformation from fossil-fuel stalwart to the country’s largest single-site renewable electricity generator. This plan presented a massive engineering challenge for Drax, with significant amounts of new knowledge quickly needed.

Fifteen years later, three of its generating units now run entirely on compressed wood pellets, a form of biomass, while coal has been relegated to stepping in only to cover spikes in demand and improve system stability.

Now Drax has converted a fourth unit from coal to biomass. This development represents the passing of a two thirds marker for the power station’s coal-free ambitions and adds 600-plus megawatts (MW) of renewable electricity to Great Britain’s national transmission system.

Building on the past

Drax first converted a coal unit to biomass in 2013, with two more following in 2014 and 2016. This put Drax in an interesting position going into a new conversion: on one hand, it is one of the most experienced generators in the world when it comes to dealing with and upgrading to biomass. On the other, it’s still relatively new to the low carbon fuel compared with its dealings with coal.

Adam Nicholson

“We’ve decades of understanding of how to use coal, but we’ve only been operating with biomass since we started the full conversion trials in 2011,” says Adam Nicholson, Section Head for Process Performance at Drax Power. “We’ve got few running hours under our belts with the new fuel versus the hundreds of man years of coal knowledge and operation all around the country.”

When converting a generating unit, the steam turbine and generator itself remain the same. The difference is all in the material being delivered, stored, crushed and blown into the boiler and burned to heat up water and create steam. And because biomass can be a volatile substance – much more so than coal – this process must be a careful one.

Drax could build on the learnings and equipment it had already developed for biomass such as specially built trains and pulverising mills, but storage proved a bigger issue. The giant biomass domes at Drax that make up the EcoStore are advanced technological structures carefully attuned to storing biomass, but for Unit 4, they were off limits.

Instead Drax engineers had to come up with another solution.

The journey of a pellet through the power station

Normally wood pellets are brought into Drax by train, unloaded and stored in the biomass domes before travelling through the power station to the mills and then boilers. Unit 4, however, sits in the second half of the station – built 12 years after the first. This slight change in location presented a problem.

“There’s no link from the eco store to Unit 4 at all,” explains Nicholson. “You can’t use the storage domes and that whole infrastructure to get anything to Unit 4.”

Drax engineers set about designing a new conveyor system that could connect the domes to the mills and boiler that powers Unit 4. After weeks of design, the team had a theoretical plan to connect the two locations with one problem: it was entirely uneconomical.

Rail unloading building 1 and storage silos

“If we were building a new plant it would be relatively easy, because you could plan properly and wouldn’t have existing equipment in the way,” says Nicholson.

“We had to plan around it and make use of the pre-existing plant.”

Within that pre-existing plant though were vital pieces of equipment, some of which had laid dormant since Drax stopped fuelling its boilers with a mixture of coal and biomass and opted instead for full unit conversions.

Drax began cofiring across all six units in 2003, using two different materials – a mix of around 5% biomass and 95% coal. A direct injection facility was added in 2005. It involved blowing crushed wood pellets into coal fuel lines from two of the power station’s 60 mills.

Then, the amount of renewable power Drax was able to generate roughly doubled in the summer of 2010 when a 400 MW co-firing facility became operational.

Back to the present day, it’s fortunate for the Unit 4 conversion that the co-firing facility includes its own rail unloading building (RUB 1) and storage silos. They are located much closer to the unit than the bigger RUB 2 and the massive biomass domes.

This solved the problem of storage but moving the required volumes of biomass through the plant without significant transport construction still posed a challenge.

Rail unloading building 1 and storage silos for Unit 4 [left], EcoStore biomass domes for units 1-3 [right]

To tackle this the team modified a pneumatic transport system, previously tested during co-firing, to have the capability to blow entire pellets from the storage facilities around the power station at speeds of more than 20 metres per second. The success of this system proved key – it was the final piece necessary to make the conversion of Unit 4 economical.

The post-coal future

Andy Koss

For now, Drax’s fifth and sixth generating unit remain coal-powered, but are called upon less frequently. With Great Britain set to go completely coal-free by 2025, there are plans to convert these too, but as part of a system of combined cycle gas turbines and giant batteries rather than biomass powered units.

It’s an opportunity for Drax to again leverage its pre-existing plant and provide the grid with a fast acting-source of lower-carbon electricity. As with converting to biomass, it will pose a complex new engineering challenge – one that will prepare Drax to meet the future needs of grid as it continues to change and demand greater flexibility from generators.

“The speed at which the Unit 4 project has been delivered is testament to the engineering expertise, skill and ingenuity we continue to see at Drax. We’re nimble and innovative enough to meet future challenges,” says Andy Koss, Chief Executive, Drax Power.

“We may look very different in 10 or 20 years’ time, but the ethos of that innovation and agility is something that will persist.”

Repowering the remaining coal plant with gas and up to 200 MW of batteries will sit alongside research into areas such as carbon capture, use and storage (CCuS) that is all geared towards expanding Drax Power beyond a single site generator into a portfolio of flexible power production facilities.

Unit 4’s conversion is more than just a step beyond halfway for the power station’s decarbonisation, but a significant step towards becoming entirely coal-free.

Find out more about Unit 4.

How the heatwave affects electricity demand

16.5 degrees is the Goldilocks temperature for the Brits – not hot enough for air-con, not too cold to put the heating on. In March we saw how the Beast from the East caused a surge in demand, now the long summer heatwave is doing the same.

June 23rd marked the start of the heatwave, with daytime temperatures surpassing 30°C in Scotland and Wales. The last week of June was 3.3°C warmer than the previous week, and demand was 860 MW higher (see chart below). This rise is equivalent to power demand from an extra 2.5 million households.

This reflects the growing role of air conditioning and refrigeration in shops, and cooling for data centres. Global electricity demand from cooling is rising dramatically, and is seen as a ‘blind spot’ in the global energy system.  This will become more important as global temperatures, and more importantly, global incomes rise. However, it is easier to deal with than cold spells during winter because demand is low and solar PV output is high.

Below 14°C, demand increases by 750 MW for every degree it gets colder as buildings need more heating. Around a tenth of British homes have electric heating, as do half of commercial and public buildings. And while the UK is not synonymous with air conditioners, demand rises by 350 MW for each degree that temperature rises above 20°C.

This effect may well grow stronger in the coming years. National Grid expect that the peak load from air conditioners will triple in the coming decade. Perhaps events such as the current prolonged heatwave may spur more households to invest in air conditioning.

Read the press release

Explore power grid data during the heatwave beginning 23rd June

Commissioned by Drax, Electric Insights is produced independently by a team of academics from Imperial College London, led by Dr Iain Staffell and facilitated by the College’s consultancy company – Imperial Consultants.

Does electricity have a smell?

Freshly baked bread, newly cut grass, sizzling bacon. Many of the world’s most evocative smells often need electricity to make them, but does electricity itself have a smell?

The short answer is no. An electric current itself doesn’t have an odour. But in instances when electricity becomes visible or audible it also creates a distinctive smell.

“The smell electricity emits is the contents of the gasses created when electricity conducts through air,” says Drax Lead Engineer Gary Preece. “In an instance of a failure on a switch board, for example, and there’s a flash of electricity, gasses are created from the charged air including ozone.”

It’s the same ozone gas that makes up the lower layer of the earth’s atmosphere and is often described as having a clean, chlorine-like, but burnt, smell. While it can sometimes be dangerous, ozone is also a very useful gas.

What is ozone?

Ozone’s scientific name is trioxide as it is made up of three oxygen molecules. While the normal oxygen we breathe is O2, ozone is O3 and is created by electricity in a similar way to how it forms naturally in the atmosphere.

There are large amounts of oxygen and nitrogen floating around in the atmosphere protecting life on earth from the sun’s intense UV radiation. These rays are so powerful they can ionise the oxygen, ripping it apart into two individual molecules. However, these lonely molecules are highly reactive and will sometimes collide and bond with nearby O2 to create ozone.

An electric current at a high voltage – given the right conditions – will conduct through the air, ionising oxygen in its wake and creating ozone, just as the sun’s UV rays do. When electricity behaves like this it’s known as a corona discharge, which makes a crackling sound and creates a visible plasma.

The most common time people may come into contact with a whiff of ozone is when a storm is approaching. Lighting is essentially a massive plasma that creates ozone as it conducts through the air, with the smell often arriving before the storm hits. It highlights quite how pungent ozone is considering humans can smell it in concentrations as low as 10 parts per billion in ordinary air. 

The concerns and capabilities of ozone

While ozone protects the planet when it’s in the atmosphere, it can be dangerous at ground level where it can also form through naturally occurring gases reacting with air pollution sources. High exposure to ozone at ground level can lead to lung, throat and breathing problems. However, because it also has a damaging effect on bacteria, ozone can be very useful in the medical field, and electricity is being used to deliberately create it.

In fact, ozone has been experimented with in medicine for more than a century, with its ability to attack and kill bacteria making it useful as a disinfectant. During the First World War it was used to treat wounds and prevent them becoming inflamed and was also found to aid blood flow.

Electricity plays an important role in almost everything we interact with on a daily basis, affecting all our senses, even smell.

6 start-ups, ideas and power plants shaping biomass

Humans have used wood as a source of fuel for over a million years. Modern biomass power, however, is a far cry from human’s early taming of fire and this is down to constant research and innovation. In fact, today it’s one of the most extensively researched areas in energy and environmental studies.

With biomass accounting for 64% of total renewable energy production in the EU in 2015, the development isn’t likely to stop. Ongoing advancements in the field are helping the technology become more sustainable and efficient in reducing emissions.

Here are seven of the projects, businesses, ideas and technologies pushing biomass further into the future:

Torrefaction – supercharging biomass pellets

When it comes to making biomass as efficient as possible it’s all down to each individual pellet. Improving what’s known as the ‘calorific value’ of each pellet increases the overall amount of energy released when they are used in a power station.

One emerging process aiming to improve this is torrefaction, which involves heating biomass to between 250 and 300 degrees Celsius in a low-oxygen environment. This drives out moisture and volatiles from woody feedstocks, straw and other biomass sources before it is turned into a black ‘biocoal’ pellet which has a very high calorific value.

This year, Estonian company Baltania is constructing the first industrial-scale torrefaction plant in the country with the target output of 160,000 tonnes of biocoal pellets per year. If it’s successful, power stations worldwide may be able to get more power from each little pellet.

bio-bean – powered by caffeine

Biofuels don’t just come from forest residues. Every day more than two billion cups of coffee are consumed globally as people get themselves caffeinated for the day ahead. In London alone, this need for daily stimulation results in more than 200,000 tonnes of coffee waste produced every year. More often than not this ends up in landfills.

bio-bean aims to change this by collecting used coffee grounds from cafes, offices and factories and recycling them into biofuels and biochemicals. The company now recycles as much as 50,000 tonnes of coffee grounds annually while one of its products, B20 biodiesel, has been used to power London buses. bio-bean also produces briquettes and pellets, which, like woody biomass, can serve as an alternative to coal.

Biomass gasification – increasing the value of biomass waste

Biogas is often seen as a promising biofuel with fewer emissions than burning fossil fuels or biomass pellets. It’s an area undergoing significant research as it points to another means of creating higher-value products from biomass matter.

The Finnish town of Vaasa is home to the world’s largest gasification plant. The facility is part of a coal plant where co-firing biogas with coal has allowed it to reduce carbon dioxide (CO2) emissions by as much as 230,000 tonnes per year.

As well as reducing emissions, co-firing allows the power plant to use 25% to 40% less coal and when demand is low in the autumn and spring months, the plant runs entirely on biogas. More than that, the forestry residues which are used to produce the biogas are sourced locally from within 100 km of site.

(As part of our transition away from coal, co-firing biomass with that fossil fuel took place at Drax Power Station from 2003 until full unit conversions became a reality in 2013.)

Lynemouth Power Station – powering the move away from coal

After 44-years, the coal-fired Lynemouth Power Station in Northumberland is the latest UK power producer converting to biomass-fuel. Set for completion this year, the plant will supply 390 MW of low-carbon electricity to the National Grid, enough to power 700,000 homes.

Every new power station conversion poses different challenges as well as the opportunity to develop new solutions, but none are as crucial as the conversion of the materials handling equipment from coal to biomass pellets. While coal can sit in the rain for long periods of time and still be used, biomass must be kept dry with storage conditions constantly monitored and adjusted to prevent sudden combustion.

At Lynemouth the handling of 1.4 million tonnes of biomass annually has required the construction of three, 40-metre high concrete storage silos, as well as extensive conveyor systems to unload and transport biomass around the plant. 

BioTrans – two birds with one stone

Energy and food are both undergoing serious changes to make them more sustainable. Danish startup BioTrans is tackling both challenges by using one of the food industry’s key pain points – wastage – to create energy with its biogas systems.

The company installs systems that collect leftover food from restaurants and canteens and stores it in odour-proof tanks before collecting and turning it into biogas for heating and electricity production. More than just utilising this waste stream, the by-product of the gasification process can also be sold as a fertiliser.

Drax and C-Capture – cutting emissions from the source

Carbon capture, usage and storage (CCUS) is one of the most important fields in the energy sector today. The technology’s ability to capture CO2 from the electricity generation process and turn it into a revenue source before it can enter the atmosphere means it’s attracting significant investment and research.

Drax is partnering with C-Capture, a company spun out of the University of Leeds’ chemistry department, to trial a new form of CCUS. The pilot scheme will launch in November and aims to capture a tonne of CO2 per day from one of Drax’s biomass units.

C-Capture’s technology could make the process of capturing and storing CO2 less costly and energy intensive. It does this using a specially developed solvent capable of isolating CO2 before being recycled through the system and capturing more.

If the pilot proves successful, the technology could be implemented at an industrial scale, seeing up to 40% of the CO2 in the flue gases from Drax’s biomass units captured and stored. If the technology tested at Drax leads to the construction of a purpose-built carbon capture unit elsewhere, scientists and engineers at C-Capture believe the CO2 captured could exceed 90%.

Back in North Yorkshire, the eventual goal is negative carbon emissions from Drax Power Station – its biomass units already deliver carbon savings of more than 80% compared to when they used coal. And if a new revenue stream can be developed from the sale of the carbon captured then the power produced from biomass at the power station could become even more cost effective.

With thanks to Biomass UK and The European Biomass Association (AEBIOM).

Keeping the electricity system’s voltage stable

Electricity high voltage sign

In day-to-day life, the electricity system normally plays a consistent, unfluctuating role, powering the same things, in the same way. However, behind the scenes electricity generation is a constant balancing act to keep the grid stable.

Power stations themselves are like living animals, in need of continuous adjustment. Transmission networks need continual maintenance and keeping the whole grid at a frequency of 50 Hz takes careful monitoring and fine-tuning.

One of the other constant challenges for Great Britain’s electricity system is keeping voltage under control.

Keeping the volts in check

Voltage is a way of expressing the potential difference in charge between two points in an electrical field. In more simplistic terms, it acts as the pressure that pushes charged electrons (known as the current) through an electric circuit. 

Great Britain’s National Grid system runs at a voltage of 400 kilovolts (kV) and 275kV (Scotland also uses 132kV). It is then reduced in a series of steps by transformers to levels suitable for supply to customers, for example 11kV for heavy industrial or 230 volts (V) when delivered to homes by regional distribution networks.

UK electricity voltage system

Keeping the voltage steady requires careful management. A deviation as small as 5% above or below can lead to increased wear and tear of equipment – and additional maintenance costs. Or even large-scale blackouts. Power stations such as Drax can control the voltage level through what’s known as reactive power.

“If voltage is high, absorbing reactive power back into the generator reduces it,” says Drax Lead Engineer Gary Preece. “By contrast, generating reactive power increases the voltage.”

Reactive power is made in an electricity generator alongside ‘active power’ (the electricity that powers our lights and devices) and National Grid can request generators such as Drax to either absorb or produce more of it as it’s needed to control voltage.

So how is a generator spinning at 3,000 rpm switched from producing to absorbing reactive power? All it takes is the turn of a tap.

Absorbing reactive power

Taps along a transformer allow a certain portion of the winding – which make up a transformer’s active part with the core – to be selected or unselected. This allows the transformer to alter what’s known as the ‘phase angle’, which refers to the relationship between apparent power (made up of reactive power and active power) and active power. This change in the phase angle regulates the ‘power factor’.

Power factor is measured between 0 and 1. Between 1 and 0 lagging means a generator is producing reactive power and increasing overall voltage, whereas between 1 and 0 leading means it is absorbing reactive power and reducing voltage.

That absorbed reactive power doesn’t just disappear, rather it transfers to heat at the back end of the power station’s generator. “Temperatures can be in excess of 60 degree Celsius,” says Preece. “There’s also a lot of vibration caused by the changes in flux at the end of the generator, this can cause long term damage to the winding.”

As the generators continue to produce active power while absorbing reactive power the conditions begin to reduce efficiency and, if prolonged, begin to damage the machines. Drax’s advantage here is that it operates six turbines, all of which are capable of switching between delivering or absorbing reactive power, or vice versa, in under two minutes.

UK electricity grid

Voltage management in a changing grid

The changing nature of Great Britain’s energy supply means voltage management is trickier than ever. Voltage creeps up when power lines are lightly loaded. The increase of decentralised generation – such as solar panels and small-scale onshore wind farms operating to directly supply specific localities or a number of customers embedded on regional electricity networks –  means this is becoming more common around the grid. This creates a greater demand for the kind of reactive power absorption and voltage management that Drax Power Station carries out.

Grid-scale batteries are being increasingly developed as a means of storing power from weather dependent renewable sources. This power can then be pumped onto the grid when demand is high. In a similar manner, these storage systems can also absorb reactive power when there’s too much on the system and discharge it when it’s needed – bringing the voltage down and up respectively.

Electricity storage

“The trouble is, grid-scale battery storage systems need to be absolutely huge, and a 100 MW facility would be close to the size of football field and double stacked,” explains Preece. “They are also not synchronised to the grid as a thermal turbine generator would be.” Subsequently there is no contribution to inertia.

As Great Britain’s power system continues to evolve, maintaining its stability also needs to adapt. Where once the challenge lay in keeping voltage high and enough reactive power on the grid, today it’s absorbing reactive power and keeping voltage down. It highlights the need for thermal generators that are designed to quickly switch between generating and absorbing to support the wider network.

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 reserve powersystem inertiablack start, reactive power and frequency response. 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.

Can we see electricity?

A 14th century carrack quietly sails through the currents of the Atlantic Ocean in the middle of the night. Its navigation relies on the stars shining above, its power on the wind blowing behind. It’s a far cry from the technologically advanced vessels sailing today’s seas.

It was here, long before civilisation began using and generating electricity, that the ghostly, blue-white glow of electricity acting upon air molecules was often seen as it hovered around ships’ masts.

This phenomenon is known as St. Elmo’s Fire, after Saint Erasmus of Formia – the patron saint of sailors – and occurs following thunderstorms when the electric field still present around an object (such as a lightning rod or a ship’s mast) causes air molecules to break up and become charged, creating what’s known as a plasma.

St. Elmo’s fire on a cockpit window

For sailors in an era long before satellite guidance it was a good omen. What they didn’t realise, however, was it was one of the rare instances when electricity acts in a way that changes it from an unseen force to something we can see, hear and even smell.

The science behind seeing electricity

Normally, we can’t see electricity. It’s like gravity – an invisible force we only recognise when it acts upon other objects. In the instance of electricity, the most common way it affects objects is by charging electrons, and because these are so small, so plentiful and move so quickly once charged, they are all but invisible to the naked human eye.

However, there are instances when conditions enable an electric current to conduct through the air, which can create sound and generate a visible plasma.

“You can see electricity in certain instances because it’s ionising the air,” says Drax Lead Engineer Gary Preece. In the process of ionising, the molecules that make up air become electrically charged, which can create a plasma.

“The electric current is able to bridge the air gap through the ionised air and to earth,” explains Preece. “You need to have that path to earth for it to create a spark.”

It’s a similar process to how a spark plug works or how lightning becomes visible. While there is still scientific debate around how clouds become electrically charged, the flashes seen on the ground are caused by discharges between clouds, or from clouds to the earth, creating a very hot and bright plasma.

The atmospheric conditions of our earth being largely oxygen and nitrogen give lightning a whitish-blue colour, like St. Elmo’s Fire. Altering these conditions so electricity passes through a gas such as neon changes the colour to a red-orangey shade, which is the principle on which neon lights and signs are built. To achieve different colours, different gases such as mercury and helium are used to fill the tube.

Long before we learned how to manipulate electricity to create different coloured signs we were battling with how to create visible, useful electricity. And it began with the use of arcs.

The architecture of electric arcs

Electric arcs occur when an electric current bridges an air gap. While air is an insulator, electricity’s constant attempts to conduct to earth sometimes enable it to find paths through it, ionising the air molecules and creating a visible plasma bridge along the way. The higher the voltage, the greater the distance it can arc between electrodes.

This property of electricity presents dangers such as arc ‘flashes’, which can occur during electrical faults or short circuit conditions and expel huge amounts of energy, sometimes creating temperatures as high as 35,000 degrees Fahrenheit – hotter than the sun’s surface.

When controlled, electrical arcs can be very useful. These bright glowing bridges were used in the first practical electric lights after Humphry Davy began showcasing the technology in the early 19th century.

But the need to replace carbon electrodes frequently, their buzzing sound and the resultant carbon monoxide emissions meant the technology was soon replaced with the incandescent bulb.

Today arcing is used in welding and in more sophisticated plasma cutting, which focuses a concentrated jet of hot plasma and can make highly precise cuts, while arc furnaces are used in industrial conditions such as steel making.

In fact, some thought has even gone into how we could use an incredibly powerful beam of plasma to create a working lightsabre. And although compelling, the theory of creating this super advanced Star Wars technology is far from being a practical possibility.

In the 14th century seeing electricity was a rare and positive omen. Today, seeing electricity has become far more common, yet when it does happen – through plasma spheres, neon lighting or naturally occurring lightning – the effect is the same: human wonder at seeing an awe-inspiring and seldom-seen force.

Why does electricity have a sound?

On cold, misty mornings, the powerlines, pylons and transformers that make up Great Britain’s electricity system sometimes sound a little different. Stand in a field under a powerline and, in the right conditions, the usual sounds of the countryside might be interrupted by the crackling of electricity.

This buzzing crackle, which can be referred to as a corona discharge, occurs when there’s a change from the normal conditions of a power line’s insulators enabling the electric current to partially conduct along it or through the surrounding air to earth. This can come as a result of weather conditions or deterioration of the insulators.

It’s just one of the instances where electricity changes from an unseen force powering our lights and devices to something we can hear, see and even smell.

Why can we hear electricity?

The source of electricity’s sound is also determined by one of its inherent properties: frequency. Frequency is the measurement of multiple occurrences from events, such as sound waves from vibrations, over a period of time. Any equipment that has a frequency causing mechanical parts to undergo repeated change can be audible.

For example, if we hit a cymbal with a drumstick we can hear a crash because of the frequency of the vibrations the mechanical part (in this case the cymbal) makes. We hear a guitar because its strings are plucked and pulled to create vibration at different frequencies. And we can hear an audible hum in a transformer because electric currents affect its internal structure and cause vibrations.

The buzzy tone this creates can be referred to as ‘mains hum’ and is ever present, although not always perceptible to the human ear. It becomes audible, however, when electricity (specifically alternating current – AC) is applied to a transformer.

Transformers are made of lengths of copper or aluminium, which are wound around a steel laminated core. When AC is applied it magnetises the core and causes steel laminations in the transformer to expand and contract in a process known as magnetostriction. Although only small physical changes, these movements are enough to cause vibration, which in turn creates an audible hum.

The crackling overhead

With more than 7,200 km of overhead powerlines humming away constantly around the country, corona discharges are inevitable and common.

This happens when part of the insulators on a high-voltage line begins to deteriorate, is exposed to weather conditions, is damaged or contaminated, allowing electricity to partially flow along it. The surrounding air becomes electrically charged through a process known as ionisation and causes molecules to become charged and collide.

It’s these collisions in the air that make the corona audible. It can also be visible and gives off a distinct smell of ozone, the gas produced when air is ionised.

Although not dangerous to someone on the ground below, if the insulator on the powerline is left to deteriorate further it can fail completely, leading to earth faults that trip power systems.

Making use of electric hums

The sounds electricity creates may seem like a nuisance but they can also have important uses. One of the most innovative applications is in forensic analysis.

A technique called Electric Network Frequency (ENF) enables forensic scientists to validate audio recording by observing the frequency of the mains hum picked up by audio recordings, which is not audible to humans.

By comparing the frequency of the hum in a recording to a database of the country’s frequencies at given times, it’s possible to verify when and in which country the recording took place and detect any editing.

It highlights not only an innovative use of electricity, but just how pervasive and consistent a presence it is. So, while the ebb and flow of electricity through our lives often goes on without thought, it is always there, humming away while it powers modern life in Great Britain.