100400 – Электроснабжение (The Electric Power Supply)

ELECTRICITY IN AGRICULTURE (8733 characters)

Electric power has had an impact on modern agriculture that has been at least as significant as that of either steam or gasoline, because electricity in its nature is far more versatile than the earlier power sources. Although there had long been scientific interest on the effects electricity had on plant growth, especially after the development of electric lamps, it was the development of the electric motor that really gained the interest of the farming community. Some authorities saw its value to farmers as early as 1870.

Electrical Сooperatives

Despite the obvious advantages of the other, more available power sources, progressive farmers in a number of countries were determined to exploit the possibilities of electricity on their farms. To get electricity, farmers formed cooperatives that either bought bulk power from existing facilities or built their own generating stations. It is believed that the first such cooperatives were formed in Japan in 1900, followed by similar organizations in Germany in 1901.

These farmer cooperatives not only initiated rural electrification as such but provided the basis for its future development. From these small beginnings the progress of rural electrification, though necessarily slow, steadily gained impetus until, in the 1920s, public opinion eventually compelled governments to consider the development of rural electrification on a national basis. Today in the most advanced countries virtually all rural premises – domestic, commercial, industrial, and farms – have an adequate supply of electricity.

Early applications of electricity were of necessity restricted to power and some lighting, although the full value of lighting was not completely realized for years. Electric motors were used to drive barn machinery, chaffcutters and root cutters, cattle cake and grain crushers, and water pumps. Electricity's ease of operation and low maintenance showed savings in time and labour. It was not long before the electric motor began to replace the mobile steam engine on threshing, winnowing, and other crop-processing equipment outside the barn.

In the fields, a number of electrically driven, rope-haulage plowing installations, some of them quite large, came into use in several European countries. These systems, however, did not stand the test of time or competition from the mobile internal-combustion-driven tractor.

Electricity From History of Technology

The development of electricity as a source of power preceded this conjunction with steam power late in the 19th century. The pioneering work had been done by an international collection of scientists including Benjamin Franklin of Pennsylvania, Alessandro Volta of the University of Pavia, Italy, and Michael Faraday of Britain. It was the latter who had demonstrated the nature of the elusive relationship between electricity and magnetism in 1831, and his experiments provided the point of departure for both the mechanical generation of electric current, previously available only from chemical reactions within voltaic piles or batteries, and the utilization of such current in electric motors.

Both the mechanical generator and the motor depend on the rotation of a continuous coil of conducting wire between the poles of a strong magnet: turning the coil produces a current in it, while passing a current through the coil causes it to turn. Both generators and motors underwent substantial development in the middle decades of the 19th century. In particular, French, German, Belgian, and Swiss engineers evolved the most satisfactory forms of armature (the coil of wire) and produced the dynamo, which made the large-scale generation of electricity commercially feasible.

The next problem was that of finding a market. In Britain, with its now well-established tradition of steam power, coal, and coal gas, such a market was not immediately obvious. But in continental Europe and North America there was more scope for experiment. In the United States Thomas Edison applied his inventive genius to finding fresh uses for electricity, and his development of the carbon-filament lamp showed how this form of energy could rival gas as a domestic illuminant. The problem had been that electricity had been used successfully for large installations such as lighthouses in which arc lamps had been powered by generators on the premises, but no way of subdividing the electric light

into many small units had been devised.

The principle of the filament lamp was that a thin conductor could be made incandescent by an electric current provided that it was sealed in a vacuum to keep it from burning out. Edison and the English chemist Sir Joseph Swan experimented with various materials for the filament and both chose carbon. The result was a highly successful small lamp, which could be varied in size for any sort of requirement. It is relevant that the success of the carbon-filament lamp did not immediately mean the supersession of gas lighting. Coal gas had first been used for lighting by William Murdock at his home in Redruth, Cornwall, where he was the agent for the Boulton and Watt company, in 1792. When he moved to the headquarters of the firm at Soho in Birmingham in 1798, Matthew Boulton authorized him to experiment in lighting the buildings there by gas, and gas lighting was subsequently adopted by firms and towns all over Britain in the first half of the 19^th century.

Lighting was normally provided by a fishtail jet of burning gas, but under the stimulus of competition from electric lighting the quality of gas lighting was greatly enhanced by the invention of the gas mantle. Thus improved, gas lighting remained popular for some forms of street lighting until the middle of the 20th century. Lighting alone could not provide an economical market for electricity because its use was confined to the hours of darkness. Successful commercial generation depended upon the development of other uses for electricity, and particularly on electric traction. The popularity of urban electric tramways and the adoption of electric traction on subway systems such as the London Underground thus coincided with the widespread construction of generating equipment in the late 1880s and 1890s. The subsequent spread of this form of energy is one of the most remarkable technological success stories of the 20th century, but most of the basic techniques of generation, distribution, and utilization had been mastered by the end of the 19th century.

All the principles of generating electricity had been worked out in the 19th century, but by its end these had only just begun to produce electricity on a large scale. The 20th century had witnessed a colossal expansion of electrical power generation and distribution. The general pattern had been toward ever-larger units of production, using steam from coal- or oil-fired boilers. Economies of scale and the greater physical efficiency achieved as higher steam temperatures and pressures were attained both reinforced this tendency. U.S. experience indicates the trend: in the first decade of the century a generating unit with a capacity of 25,000 kilowatts with pressures up to 200-300 pounds per square inch at 400⁰-500⁰ F (about 200⁰-265⁰ C) was considered large, but by 1930 the largest unit was 208,000 kilowatts, with pressures of 1,200 pounds per square inch at a temperature of 725⁰ F, while the amount of fuel necessary to produce a kilowatt-hour of electricity and the price to the consumer had fallen dramatically.

As the market for electricity increased, so did the distance over which it was transmitted, and the efficiency of transmission required higher and higher voltages. The small direct-current generators of early urban power systems were abandoned in favour of alternating-current systems, which could be adapted more readily to high voltages. Transmission over a line of 155 miles (250 kilometres) was established in California in 1908 at 110,000 volts; Hoover Dam in the 1930s used a line of 300 miles (480 kilometres) at 287,000 volts. The latter case may serve as a reminder that hydroelectric power, using a fall of water to drive water turbines, has been developed to generate electricity where the climate and topography make it possible to combine production with convenient transmission to a market. Remarkable levels of efficiency have been achieved in modern plants. One important consequence of the ever-expanding consumption of electricity in the industrialized countries has been the linking of local systems to provide vast power grids, or pools, within which power can be shifted easily to meet changing local needs for current. (Copyright © 1994-2000 Encyclopædia Britannica, Inc.)