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Note: This is an abridged version of a chapter in British Commerce and Industry 1934
The Central Electricity Board was set up early in 1927. Two years previously the Government appointed a Committee, with Lord Weir as chairman, to review the national problem of the supply of electrical energy and report on the policy that should be adopted to ensure the most efficient and effective development of the supply of electricity. The main recommendations of the Committee were: that a national system of main transmission lines, designated the "Grid," should be established for the purpose of interconnecting the systems of all the public supply authorities in the country and enabling them to be supplied, on a wholesale basis, with electricity produced at the most efficient stations; that an executive body - the Central Electricity Board — which should be responsible for the erection and operation of the "Grid" and should direct the operations of the station "selected" to feed it, should be set up, and that standardization of frequency of the alternating current systems in the country should be undertaken as part of a comprehensive scheme for improving our existing electricity system. These recommendations were adopted by Parliament and given effect to by the Electricity (Supply) Act of 1926.
The Board, which comprises a chairman and seven other members appointed by the Minister of Transport, is a statutory body but not a Government department. It represents a new type of organization which combines public control with a large measure of independence in operation. It is required to render an annual report to the Minister of Transport.
For the purposes of the "Grid" construction programme the country was divided into ten main areas, namely: North Scotland, Central Scotland, South Scotland, North- East England, North-West England and North Wales, Mid-East England, Central England, East England, South-East England, and South-West England and South Wales. For each of these areas, except North Scotland, regional schemes so conceived and designed that they would dovetail into each other to complete the greater national plan were prepared and have now been completed. Construction began in Central Scotland early in 1928, and the last tower for the main transmission system was erected on the outskirts of the New Forest at the beginning of September, 1933.
In the National Power network, there are 4,000 miles of transmission lines, including 2,894 miles of primary lines operating at the high pressure of 132,000 volts, and 1,106 miles of secondary lines operating at lower voltages. The primary lines include 15 route miles of cable and the secondary line 102 route miles of cable laid within the London area. In the system there are 26,265 towers—roughly seven per mile — averaging 75 feet in height and over three tons in weight.
Approximately 60 rivers had to be crossed, involving the construction of special towers of varying height. The largest towers in the Grid are those for the Thames crossing at Dagenham. They are 487 feet high and weigh 290 tons each. The span of the conductors between the towers is 3,060 feet. This exceeds by 10 feet the length of the span across the Forth at Kincardine, where the towers are 298 feet high. A single tower 362 feet high is used for the crossing of the River Roding at Barking Creek. Other notable towers in the system are those for the Severn crossing at Upper Arlingham, 300 feet; the Clyde crossing at Yoker, 280 feet, and there are many others between 200 and 300 feet high.
When the Board was constituted and began its work, electricity for public supply was produced in approximately 500 generating stations belonging to authorized undertakings throughout the country, and the total number contemplated when the scheme of reorganization is complete is 135. The largest generating plant in the Grid, with a capacity of 390,000 kilowatts, is the Barking station of the County of London Electric Supply Co, while several of the other selected stations are designed for an output of between 200,000 and 350,000 kilowatts. There are 273 transforming and switching stations or "Grid Points," with a total capacity of 11,000,000 horse-power. The largest installation of transformers is also at Barking, where there are four sets of 60,000 and six of 30,000 kilo-voltamperes, while at the new Clarence Dock station in Liverpool, the first 75,000 kVA. transformers have been installed. In area and number of switches, Northfleet, in the South-East England scheme, is the largest 132,000-volt switching station in the Grid.
Standardization of frequency is necessary to effective interconnection of the national system, and the national standard is fixed at 50 cycles per second. Certain areas, particularly the Clyde Valley, North-East England, Central England and a part of South Wales, were developed on a non-standard basis, in some instances at a frequency of 25 cycles and in others of 40 cycles per second. The conversions, spread over a number of years, involve the rewinding of alternators and other equipment and the installation of over 1,500,000 h.p. of new electric motors in consumers' premises. The cost of standardization, which is carried out by the undertakings themselves, under the supervision of the Board, is recoverable from the entire electricity supply industry by means of a levy. This is collected by the Electricity Commissioners and refunded to the Central Electricity Board.
The first section of the Grid lines was put into service in Central Scotland early in 1930, and on 1st April, 1934, general trading under the provision of the 1926 Act was in progress in six areas aggregating nearly 41,200 square miles, supporting a population of approximately 35 million people, or 78 per cent. of the entire population of Great Britain. The system is planned to deal when fully loaded — which it is hoped will be about 1940 - with an annual output of 25,000,000,000 units, equivalent to about 500 units per head of the population.
The cost of constructing the Grid has been approximately £27,000,000 and is within 21 per cent. of the original estimates.
The construction of the National Electricity Grid occupied nearly six years, and was responsible for intensive activity in a wide and varied range of industries. Industrial ramifications extended notably to coal-mining, iron and steel manufacture, cable-making, electrical engineering, cement and pottery industries, building and contracting, and the effect of the Grid contracts upon employment directly or indirectly has been to produce over 240,000,000 man hours of work.
Upwards of 150,000 tons of steel were required, the major proportion being used for the fabrication of the transmission towers, which now straddle the country from the Grampians to the South Coast and from East Anglia to Land's End. An impressive tale of organization and labour was involved in the transport and handling of crude ore at the factories, conversion of ore in the blast furnaces into molten metal, casting into moulds, rolling and pressing into solid bars and the final transformation into the finished product required for construction.
Similar processes were necessary for the manufacture of aluminium. Approximately 12,000 tons of the metal were required for the overhead lines of the Grid transmission system. Almost the whole of this material was produced in Scotland, where, under the shadow of Ben Nevis, the reduction of aluminium is carried out at a factory supplied by hydro-electric power. The Lochaber water power scheme, which produced the energy for this purpose, is one of the largest hydro-electric undertakings in existence. From Scotland the moulded aluminium bars were transported to factories in the Midlands, where the metal was drawn into wire and stranded with steel wire for the overhead conductors.
Even more elaborate were the stages of manufacture involved in the output of copper wire required principally for making underground cables, and the sequence of smelting, refining, roughing, finishing, coiling, pickling, washing, drawing and annealing emphasizes the multifarious processes that go to the production of the high quality material required. In the smelting process the temperature of the metal is raised in a special type of furnace to 1,200 degrees C., at which stage trees are thrown in to remove the copper oxide.
Cables used in the underground portion of the Grid system are of various types, including solid-cored cables, oil-filled cables, in which the oil, introduced as an insulating agent, is maintained at a constant pressure, multi-cored cables and an experimental cable of an entirely new kind—drawn into a steel duct and surrounded by nitrogen under pressure. In the ordinary types in more general use, the processes of manufacture comprise the stranding of the wires, lapping round with paper, impregnating with oil, the application of a lead sheath and armouring with steel tape or galvanized wire.
Another interesting sidelight upon industrial activity behind the Grid construction lay in the production of porcelain insulators, of which about 200,000 strings and bushings were required. The basic materials in their composition are china clay, felspar and quartz. Finely ground, these ingredients are mixed with water, sifted in drums and filtered, the resultant mixture being pressed and moulded. Sections may be moulded and cemented to form bushings, and undergo processes of glazing and firing in kilns, whence they emerge to be ground finally to the correct size, or discs may be formed which are finally assembled in strings for overhead line work. Before leaving the factory, each insulator is subjected to an exhaustive series of tests to prove its mechanical strength and insulating properties.
Special types of transformers and switchgear are necessary to deal with the high pressures at which electricity is transmitted through the National Power network. In some cases transformers are used to increase the pressure at which it is generated, for the purpose of transmission over the primary lines in others their function is to reduce the high pressures of main transmission to voltages convenient for distribution by local undertakings, with whom rests the responsibility for bringing electricity to points where it can be supplied direct to the consumer.
The construction of transformers and switching equipment, and also of metering and control apparatus, provided a large amount of work in the various branches of the electrical engineering industry.
The component parts having been prepared, the actual erection of the Grid towers and transmission lines, apart from constructional and civil engineering problems, was comparatively straightforward. In some instances, as for example in marshy ground, the preparation of the foundations for the towers, which must be securely anchored in the earth, necessitated the additional safeguard of piles being driven deep into the soil. The assembling of the tower sections, the hoisting and bolting together of the steel framework, and the fixing of the cross-arms to carry the insulators and conductors called for the highest qualities of steadiness and nerve on the part of workmen engaged upon these operations, often at great heights above the ground. Finally, the conductors were strung between the towers and the tension of them scientifically regulated, and the transmission lines of the Grid were ready for service.
The output capacity of the 135 stations selected for permanent operating under the National Power Scheme ranges from about 10,000 kilowatts in the smallest to 390,000 kilowatts at Barking, where the steam-raising plant for the turbo-generators consumes over 1,100 tons of coal a day. Under the Grid plan, the base load will be carried chiefly by the larger stations where production is most economical. The smaller stations retained may only be run during peak periods, and shut down during week-ends when the industrial demands are low, or during the summer months when lighting and heating demands are small. The programme of eliminating entirely the smaller uneconomical stations from generation will be continued, as the circumstances and operating experience justify, until the scheme functions at maximum efficiency with the minimum number of generating stations in operation.
Provision, however, has been made for the erection of 16 new selected stations, including 5 hydro-electric stations — utilizing the water power resources in the southwest of Scotland. Of the 11 projected new steam stations, five are at different stages of construction. All of these are intended for large-scale production, and the output capacity for which they are ultimately planned ranges from 200,000 kilowatts at Ironbridge, in the Central England area, to 480,000 kw. at Battersea, the others being Clarence Dock, Liverpool, 350,000 kw.; Fulham, 300,000 kw.; and Tir John, Swansea, 240,000 kw. These great generating stations have been designed on modern lines, and embody the most up-to-date plant and equipment alike for fuel handling, steam-raising, condensing, generating and control, as well as for the prevention of atmospheric pollution by smoke, grit and combustion gases.
Battersea and Fulham are interesting examples of modern power-station construction and equipment. The fuel handling plant, electrically operated, includes a telpher or moving belt by which coal brought up the river by colliers or barges is conveyed after weighing either to the storage dump or direct to the boiler house. The boilers are equipped with automatic stokers or pulverized fuel plant, superheaters, air preheaters, economizers, forced and induced draught fans, together with smoke cleansing plant. When these stations are at full load capacity they will each require about 14 or 15 million gallons of water per hour for condensing purposes. Another striking example of power-house design is the new station at Dunston, in the North-East England area, which has been built on novel lines in steel, glass and concrete.
One of the results of the Grid has been to afford an important outlet for the water power resources of the country. A large quantity of energy from the hydro-electric stations of the Grampian Electricity Co in North Scotland is fed into the Grid in Central Scotland, while the selection in South Scotland of five water power stations under construction by the Galloway Water Power Company establishes a direct association with the national power system, provision being made for the output being fed into the Grid primary line between Carlisle and Kilmarnock. The Grid is also linked up at Crewe with the hydro-electric stations in North Wales.
Through the interconnected transmission system, which is capable of expansion whenever the demand renders it necessary, unlimited quantities of electricity are made available alike for industrial requirements in the great cities and urban districts and in outlying country areas to which an extension of supplies under the former uncoordinated system of generation was only a remote possibility. The Grid, particularly in its lower voltage sections, is being tapped at convenient points, and, by placing at the command of scattered communities in the countryside all the advantages of an amenity hitherto only within the reach of the urban population, is gradually effecting a revolution in rural life. There are now, for instance, over 5,000 electrified farms in Great Britain, while the development of rural distribution systems, notably in South Scotland, Cumberland, Westmorland, Cheshire, Shropshire, Bedfordshire, East Anglia and South-East England, is rapidly adding to the number of rural users of electricity.
In the larger power stations energy is generated at a voltage of, say, 11,000 volts, and then passed to a transformer, where it is stepped-up to 132,000 volts for transmission to a switching station. At a switching station which acts as a main distributing centre, the power may be stepped-down to 66,000 volts, 33,000 volts or lower voltages before it is transmitted over secondary lines to local supply undertakings. Close watch is kept on the incoming and outgoing power, and by means of elaborate metering apparatus, an accurate register is kept of the quantities received and dispatched, the records of consumption being printed automatically every half hour.
From the main load dispatching stations the power is transmitted to the "grid points" at which it is tapped off and further reduced for local distribution. For power purposes, domestic and other uses the supply authorities step down the voltage to the various pressures at which it may be required by their consumers. An electric railway or factory may want energy at comparatively high voltages farms and villages will want it at lower voltages suitable for their everyday needs. Different types of transformers are adopted to meet the varying needs of the situation. In the case of villages the transformers are sometimes placed in kiosks, while for individual farms or small groups of consumers, compact pole transformers are adequate for the purpose.
The whole efficiency of the Grid system is dependent upon the exercise of effective control of generation and transmission. This has been provided for by the establishment at strategic points in each area of a fully equipped control room, connected by private telephone lines with all the generating stations and grid points in the area. By a combination of switch-board, dials, light signals and telephones, controllers in these nerve centres are kept in constant touch with the working of each generating station, and with the fluctuating state of demand through the various switching stations. They are thus enabled so to order the operations of generation and transmission that the load may be spread over the interconnected stations to give the most economical results consistent with adequate and reliable service. The most efficient generating stations can be loaded up to produce the maximum output of units and the smaller stations used only for shorter periods to meet peak load demands.
Thus will the production and bulk transmission of energy be controlled, and electricity made available without interruption in any part of the country for the service of more than 40,000,000 people.
1948 Successor organisation: British Electricity Authority