The story of Electricity Generation from pipelines to pylons
Part 1: The evolution of electrical mains power, and where UK power comes from today.
In the UK we are fortunate enough to enjoy virtually uninterrupted electricity, provided by one of the world's largest interconnected electrical systems which links our power stations together to form the National Grid. The high quality of Britain's electricity supply is taken for granted by us all, although for both the micro-electronics enthusiast and the general public much mystique surrounds the way in which electrical power is created and delivered safely to our homes.
In this feature, supported by the expertise of the international power generation company National Power plc, Alan Winstanley describes the high technology involved in generating power - from a gas pipeline to the turbines and generators and then to the electricity pylon and beyond! We also examine in close-up some of the techniques related to the provision of a 230V supply directly to our housing and industry.
National Power generously granted the writer unlimited access to all parts of a modern 650MW gas-fired power station - Killingholme "A" - and provided a much-needed insight illustrating where our "juice" actually flows from. If ever you have wondered what "neutral" really means, why the earth (ground) plays such a vital role in safety, or why an electricity power station would ever need gas, or if you just want to brush up on some fundamental theory, this article provides background which is essential reading for electronics users and consumers everywhere.
National Power plc demerged on 2 October 2000 into two companies, International Power plc and Innogy Holdings plc. In 2002 the European firm RWE AG acquired Innogy Holdings plc. RWE Innogy owns many familiar British electricity brands, including National Power and Yorkshire Electicity. At the time of writing (Feb. 2011) Killingholme "A" power station is operated by Centrica. A neighbouring larger Killingholme "B" site is owned by E.ON.
Please note! This article is based on the British 230V electrical distribution system. In fact Britain built many such power grids around the world, so what’s written here might apply where you live but there may be differences. However there are differences in terminology and voltages, so please bear that in mind. The term "earth" is often used in Britain to mean "ground" and can be used interchangeably. Some details about the commercial distribution of power in Britain have changed since this article was written.
The sight of electricity pylons marching alien-like across the countryside is an all too familiar one, yet in spite of their omnipresence it is easy to overlook the feats of heavy engineering and high technology surrounding us which are responsible for delivering electrical energy to illuminate and warm our homes, cook our food and entertain us, as well as powering our industries.
It is something of a paradox that the microelectronics enthusiast can utilise the very latest in silicon chips to create another technological masterpiece, yet if we are honest, many of us would admit to having only a fleeting knowledge about the electricity supply itself. We leave that sort of thing to electricians. We probably know (we think) that earth is, as its name suggests, connected to earth somewhere along the line, and perhaps the neutral is, er, somehow neutral. We know that the supply is "alternating", but how many have actually stopped to consider what this all really means? Or why it's like that to begin with?
After reading these articles you will know precisely how the electricity supply is generated, distributed and delivered. Although it is written with the UK 230V a.c. 50Hz. supply in mind, note that many similar principles are utilised abroad, so even if you do not reside in the UK you will find a considerable amount in common between the systems outlined here and those found in your own country (some of which are undoubtedly British-built).
The incandescent electric lamp was first produced in 1879 by Joseph Swan in England and Thomas Edison in the USA, and two years later Britain saw the advent of its first public electricity supply . Over the next fifty years some 600 supply undertakings with nearly 500 localised power stations would be created, operating at a variety of frequencies and both a.c. and d.c. voltages. In 1927 the Central Electricity Board (CEB) was appointed by statute, with a view to standardising frequencies, and also to implement an interconnection plan to improve efficiency and reduce waste. The plan involved hooking together a select number of power stations, and was completed in 1938. Later the industry was nationalised in 1948.
Over the last twenty or thirty years the power generation picture in the United Kingdom has been transformed, so to speak, having moved away from the once heavy reliance on Britain's rich supply of coal to a modern multi-fuelled power industry which is clean, efficient and dependable.
Until the early 1990's, power generation was undertaken and controlled by the Central Electricity Generating Board (the CEGB), which was primarily responsible for producing and selling power for onwards transmission to the regional electricity boards by the National Grid, the organisation which "owns the wires". From there it would be distributed to tens of millions of residential and commercial properties.
Privatisation and the arrival of market competition in 1990 introduced radical changes in the way the UK electrical supply market operated. The CEGB gave way to competing power companies - including National Power, PowerGen and the nuclear arm of the industry, British Energy. There are now some 30 or more power producers, many of which are independent or foreign owned power stations, competing for the business of nearly 23 million domestic customers. These and millions of commercial and industrial users are served by fourteen Regional Electricity Companies (RECs). The market for buying and selling electrical power has opened up at all levels, so much so that in the UK it is now possible to buy gas from electricity providers and vice versa.
Over the many decades in which we have enjoyed virtually uninterrupted electrical supplies, the power providers have gained vast experience of the likely demands which will be placed upon them at any one time by their customers. This enables the power distribution companies to plan ahead and allocate daily the various power generation resources that will be available to meet the forecasted demands. Fig. 1 shows how according to National Power various fuel types are available in "layers" to meet this demand, which in the UK totals nearly 70,000 Megawatts (MW) (1999). The graph also shows how the resources are divided amongst various fuel types.
|Fig 1 UK Electricity plant portfolio (98/ 99) showing how different sources of power are brought on-stream as demand increases. Nuclear is 'on all the time' whilst coal-oil and pumped storage (hydro) are used to 'top up' the capacity available. National Power|
Underpinning the country's supply capability are both gas and nuclear fuel sources which produce a constant 30,000MW between them (1999) and form the bedrock of Britain's available capacity. Also providing nearly 5,000MW of capacity are what are termed "interconnectors", which relate to the connections made by the National Grid to both Scotland and France: yes, a certain proportion of our power is imported, though the same wires could be used to export surplus electricity as well. Roughly 2,000MW of interconnected power is available via the Cross-Channel Link, a pair of undersea 45 km long cables completed in 1986.
The rest of the UK's electrical capacity is provided by coal, oil, OCGT (open-cycle gas turbine) and hydro-electric power, noting from Fig. 1 that the capacity of these sources dwindles in terms of utilisation: they form the buffer which is primarily used for the "top up" needed to meet peak surges. For most of the time, we rely on nuclear power, gas-fired power plants and imported electricity (the 'interconnects') which are 100% utilised.
The daily demands for electrical power rise and fall during the day, and the weather and many other events - such as the advertising breaks in favourite TV soaps - can trigger a huge surge in demand when Britons head for the electric kettle. These TV-related surges are known as "TV pick ups". The average Brit. will also decide to turn on the electric lights in the evening only when a commercial break occurs!
It is the function of the National Grid Control Centre, based at Reading, to match the demands placed by its customers with the available capacity and to cope with anticipated TV pick ups. According to National Grid figures (to 1999), the largest recorded TV pick-up of 2,800MW occurred in the World Cup Semi Final in July 1990 (England v. West Germany). To maintain stability the control process may also require electricity production to be reduced when demand falls: the funeral of Princess Diana caused a major drop of 1,000MW in normal power consumption when all daily activity stopped in the UK.
The task of matching supply and demand is called "generation despatch" and involves not only the National Grid being kept posted by data links showing the availability of power from all its suppliers, but also at what price: electricity is bargained in Pounds per MegaWatt Hour and power generation companies have to commit to a price for filling half-hour slots for the 24 hours ahead. This bidding process occurs every morning when the power plants notify the National Grid of their availability and pricing for the day.
As you would expect in a privatised market economy, the "bulk" price charged by generators varies depending on demand. On a typical November day (for example) it could rise from around £33 ($54) per MegaWatt Hour (MWH) to roughly £45 ($74)/ MWH at peak times of the day - which, incidentally, is at tea time, when demand peaks dramatically at 17:30 hours. By way of comparison, depending on one's location a domestic electrical "unit" costs (at 1999 figures) 6.45 pence (10.6 cents), which equates to œ64.50 or $106.42/ MWH. In 2011 they are nearly double that.
Trends from preceding weeks, months and even years are taken into account as well and forecasts are accurate to within a couple of percentage points. Any event which is forecast to trigger a rise in power demand - say a televised World Cup - is brought into the equation, as are other factors including weather forecasts, seasonal trends and even the day of the week.
|Fig 2 How a 24-hour demand, peaking at 17.30 hours, is met by the electricity industry. National Power.|
In Fig. 2 above, National Power illustrates how peak demands over a typical 24 hour period are gradually topped up as more plant is brought on stream to cope, culminating with the short-term use of pumped storage (water caverns) to generate hydroelectric power at peak times (around 6 p.m.). Note that nuclear and gas-fired power provides a constant output, and only as demands soar will larger coal and oil-fired stations be brought onto the system to meet peak surges. A "pumped storage" installation in Dinorwig, Wales can also be brought on stream within ten seconds, to cater for daily peaks in demand, and this cushion has helped to reduce the need to have spare generator plant constantly running to meet unanticipated surges in demand, see Fig. 3 below. All power plants are identified in an "order of merit' table which highlights the individual cost of power generated by the various power plants.
|Fig. 3 Daily demands are bought by the National Grid in half-hour blocks from electricity producers. The graph, produced daily, depicts several factors including the purchase price of electricity (1998). National Power|
Hence there are low merit (high cost) and high merit (low cost) plants which depend on the type of fuel used. In addition, the National Grid will take into account the dynamic parameters of the plant, such as loading rates, and whether the turbines are hot or cold. It can be cheaper to run a more expensive "hot" machine than a cheaper cold machine.
Killingholme "A" CCGT Power Station
In the remaining sections, we'll examine how electrical energy is generated, transmitted and delivered to your home. The feature offers a broad-interest view of both electricity generation as well as distribution, and is designed to offer an insight into electrical power divided in two stages: from gas pipeline to electricity pylon, and then examining how electricity is delivered directly into your home.
In particular we will be looking at one of Britain's newer gas-fired power stations: National Power's Killingholme "A" is situated on the banks of the River Humber. Killingholme "A" was National Power's first gas turbine plant commissioned in 1993. This 650MW plant runs as a "base load" operation, which means that Killingholme "A" provides a constant output that forms some of the everyday "bread and butter" of the United Kingdom's electrical capacity. Its performance won Killingholme "A" the National Power Availability Prize.
National Power has strong international links and is heavily involved with the export of technological know-how, including the construction and joint operation of power plants in other countries, notably the USA, Europe and China. The power station at Killingholme also has an impressive array of links with local educational and environmental projects, having funded a wide variety of nature conservation drives in association with both local and national authorities. A new fully staffed visitor's centre, an educational garden and close associations which have been carefully nurtured with neighbouring schools and further education help ensure that Killingholme "A" plays an environmentally aware and responsible role in the community.
National Power generously granted the writer unlimited access to the entire power plant and the author is extremely grateful for the abundant levels of assistance which have been provided by Station Manager Keith Ulyett and National Power engineer Richard Power. Both offered much enthusiastic help and hospitality during the preparation of this special feature. The writer has spent several days on-site, including a day during a major outage (overhaul) when several key parts of the power plant were in the process of being stripped down for inspection and maintenance. This was therefore a timely opportunity to delve into the inner workings of a power plant.
The power station subsequently changed hands and at the time of writing (Feb. 2011) is now operated by Centrica Energy.
Next, transformer and power transmission basics are explored.