ELECTRICAL POWER INDYSTRY
Using energy has been a key issue in the process of the development of our human society since the old times when people started to control fire. But one of the most prominent sources that changed the life of the whole world was the discovery of the most efficient energy source – the electricity. In our modern world electricity is used for industry and agriculture, communication and transportation, and for everyday use.
The development of electricity dates back to the late 17th century and the great discovery of the power source of energy was made by William Gilbert. A great number of further important discoveries were made over the next two centuries – among them are a light bulb and electromagnetic induction principle. The start of the electrical industry began in 1881 when the first power station in the world was constructed at Godalming in England. Then in 1882 the great inventor Thomas Edison and his Edison Electric Light Company started their first steam-powered station in New York. That was the beginning of the new era of electricity that changed the way people lived. By 1890 there were thousands of power systems in Europe and the USA.
But what is the electricity? From the scientific point of view, the electricity is a particular set of physical phenomena which is characterized by the presence and the distinctive flow of electric charge. It is created when the small particles – electrons move between the atoms. This process creates an electric current. And this current is used to energize different kinds of equipment. Electrical Power Industry can be fair enough called a backbone of the modern industry and everyday life.
We use electrical power for heating, cooling and lighting our houses, for cooking food, and for numerous devices and gadgets such TV-sets, computers and smartphones. Electrical power has become the essential necessity for the modern society. But unfortunately not all people in the world have an access to this source of energy. Millions of people in poor countries have to survive without the advantages of electrical power.
Besides the obvious advantages that electrical power brings to our life there is a definite set of threats that this modern technology causes. The process of electricity generation on different kinds of power stations often is not so harmless to the nature. One of the most efficient but dangerous means of electricity generation is a nuclear power station. Though this is one of the most effective ways to generate electricity for the needs of the society, the disastrous catastrophes in Chernobyl and Fukusima showed us how dangerous nuclear power is.
The process of nature friendly electricity generation has been developing greatly these days. Wind power, solar power and the power of the ocean are used to generate safe and cheap electricity that will be able to bring our life to the next level of evolution.
JAMES MAXWELL
In the decade 1860–1870, James Maxwell formulated his classical electromagnetic theory. He showed that light was a form of wave motion travelling with a speed dependent on the electric and magnetic properties of the medium through which it is transmitted, lie also predicted that waves longer than those of light could exist. Even before Maxwell advanced the theory that electromagnetic waves should exist, men were making use of them for other purposes besides vision. For instance, the short ultraviolet rays in sunlight provided suntans; and the heat of the sun – provided by the long infra-red rays – was often concentrated by means of a lens to start fires. After the existence of electromagnetic waves had been proved by Hertz it was discovered that they range in length from hundreds of miles down to less than a billionth of an inch. The long waves could be used to carry sounds through space; as a consequence radio was developed. A more recent development, which is related to radio, is television. Not only sounds but pictures can be transmitted at a distance because of electromagnetic waves. Another modern device, developed to send out electromagnetic waves and to receive the echoes when they return, is radar, since the speed of electromagnetic waves is known, the time it takes for an echo to return to the radar set can tell the operator how far away a plane is from his set. Radar is given the credit for saving Great Britain during World War II, for it warned of enemy planes. Thus James Maxwell had made discoveries that later protected his homeland. Today with radio, television, radar, and communication with outer space making use of these waves, it is easy to realize why James Maxwell is now considered one of the great scientists of all time. BALL LIGHTNING It is quite probable that there are several different physical forms of ball lightning, each having its own characteristic set of properties. These phenomena are rare and this rarity leads to the wide variety of descriptions of ball lightning. Lightning balls seem to appear near the end of severe electrical storms. This happens after the air has been highly ionized and is filled with electromagnetic disturbances generated by the conventional lightning. The diameters of observed lightning balls range from a few inches to rare instances of many feet. The average diameter of a ball is about 10 inches. The balls usually move by rolling or sliding along conductors such as telephone wires, fences, and other metallic objects. The lifetime of a ball of lightning may range from a few seconds to minutes. 81 One large ball was observed to hang near the base of a cloud for 15 minutes. The calculated surface temperature of a lightning ball can be as high as 5,000°C. When the ball decays, a great amount of energy is released. The Soviet physicist Pyotr Kapitsa was the first to present a reasonable explanation for the majority of the questions in a hypothesis for ball lightning. His ideas on the energy balance, on the importance of resonance phenomena, and on the fixed dimensions of "ball lightning are, well known. The theory put forward by him in 1955 starts with the description of a powerful flash of lightning at the end of a thunderstorm. It paves the way for the appearance of ball lightning at sufficient ionization of the air and the presence of vapours necessary for ionization of the rising current of air. The ionized clouds of plasma are composed of the atomic nuclei of gas stripped of their electrons. These nuclei possess their own 'periods of electromagnetic oscillations and are able to absorb the incoming external electromagnetic energy of the same period. This is known as the resonance effect. Details of Kapitsa's hypothesis include the reasoning that during the luminescence period, some energy is supplied continuously into the ball lightning and the energy source is outside the ball. This reasoning is based on the conservation of energy principle and on the realization that the ball lightning is suspended in the air with no visible link with the energy source* Thus the only source of energy is the absorption of intense outside radio waves. The resonance characteristic of the absorption process is determined by the form of the ball lightning alone and by its dimensions. For effective absorption of radio waves by the lightning ball, the natural frequence of the electromagnetic oscillations within the ball, must coincide with the natural period of the absorbed radiation. As to academician Kapitsa, his field of interests was not limited by high temperatures alone. In 1978 he was given a Noble prize for his fundamental discoveries and inventions in the field of low temperatures and superconductivity.
TRANSMISSION LINE
Although presently operating at 230 kv, the transmission line is designed and fully insulated for operation at 345 kv, using an additional conductor per phase. Provision has been made and hardware provided for the intsallation of this secondphase conductor; it will be strung prior to conversion to 345 kv, which is anticipated 60 in the course of the next 2 or 3 years. Apart from the extra-high voltage aspect, however, there are a number of features of design and construction which are worthy of mention. The first concern the use of aerial photography for acquisition of the right-of-way** as well as spacing and location of the line structures. Initial reconnaissance of the route was made by helicopter, and aerial photography was used to make final selection; then photographs of this route were obtained to a scale of 200 feet to the inch. On these photographs were superimposed all property lines, road boundaries, the boundaries of the proposed right-of-way and legal descriptions of the property traversed. Final land survey for registration purposes followed at a later date. The right-of-way acquired is 450 feet in width, to provide for two additional similar circuits at some future date. Concurrent with the selection of a suitable route was the design and fabrication of the towers. The conductor selected was 795,000 circular-mil 26/7 steel-reinforced aluminum cable, using a twin bundle per phase at 18-inch centers; phase spacing was 35 feet. The conductor was suspended from 21 unit insulator strings***, with specially designed grading rings attached at the lower ends. The maximum design tension in the conductor was one-half its ultimate strength. The maximum design loading was 1/2 inch of radial ice, plus 4 pounds per square foot wind pressure at zero degrees Fahrenheit. As the lightning incidence in this area is very low, ground wires were installed for only 1/2 mile at the line terminals. After considerable study as to the type of tower to be employed on this line, the portal type was finally selected. Fig. 26 shows a tangent tower. This type of tower offers a number of distinct advantages for this application. By the use of two masts, instead of the quadruped construction normally used, the weight of redundant steel is considerably reduced, particularly in the tower head. At extra-high voltages, this reduction becomes increasingly important. Another advantage is that the two masts offer very little obstruction to the use of agricultural equipment around the tower. This was a factor, as 59 of the 64 miles of line pass through highly cultivated farmland. The third advantage lay in the ease of erection for this type of tower. The specification called for a standard mast to be designed to meet the requirements for tangent, angle, and dead-end towers. On angle towers, the transverse load was to be taken by internal guys, and similarly, on deadend towers the conductor tension was to be taken by guys. Thus, the mast designed for the tangent tower could be used for all towers, and only separate crossarms need be detailed. This effected a considerable saving in detailing cost and simplified erection. The maximum line span was 1,222 feet and the minimum 514 feet. The average span was 995 feet. Every suspension tower was to be capable of withstanding a longitudinal load due to both conductors 61 of one phase being broken. In order to reduce the dynamic load on the tower Masts when a conductor breaks, it was decided that the crossarm should be designed to fail at 60 per cent of the actual broken-wire load, that is, a safety factor of one applied to the broken-wire load as described above. Upon failure the crossarm would swing into the line, thus reducing both the dynamic and the static load on the tower. A total of 340 towers were constructed on this line over a period of 8 months. The great majority of towers were erected by completely assembling the masts on the ground and then erecting them by means of a mobile crane. A 2-masted tower took approximately one day to assemble on the ground and 2 hours to erect. Twenty-three months after commencement the line was completed; it was energized at 280 kv on November 30, 1952.
POWER TRANSMISSION
They say that about a hundred years ago, power was never carried far away from its source. Later on, the range of transmission was expanded to a few miles. And 59 now, in a comparatively short period of time, electrical engineering has achieved so much that it is quite possible, at will, to convert mechanical energy into electrical energy and transmit the latter over hundreds of kilometres and more in any direction required. Then in a suitable locality the electric energy can be reconverted into mechanical energy whenever it is desirable. It is not difficult to understand that the above process has been made possible owing to generators, transformers and motors as well as to other necessary electrical equipment. In this connection one cannot but mention the growth of electric power generation in this country. The longest transmission line in pre-revolutionary Russia was that connecting the Klasson powerstation with Moscow. It is said to have been but 70 km long, while the pre sent Volgograd–Moscow high-tension transmission line is over 1000 kilometres long. (The reader is asked to note that the English terms "high-tension" and "high-voltage" are interchangeable.) Generally speaking, the length of high-tension transmission lines in the Soviet Union is so great that they could circle the globe six times, if not more. It goes without saying that as soon as the electric energy is produced at the power-station, it is to be transmitted over wires to the substation and then to the consumer. However, the longer the wire, the greater is its resistance to current flow. On the other hand, the higher the offered resistance, the greater are the heating losses in electric wires..One can reduce these undesirable losses in' two ways, namely, one can reduce either the resistance or the current. It is easy for us to see how we can reduce resistance: it is necessary to make use of a better conducting material and as thick wires as possible. However, such wires are calculated to require too much material and, hence, they will be too expensive. Can the current be reduced? Yes, it is quite possible to reduce the current in the transmission system by employing transformers. In effect, the waste of useful energy has been greatly decreased due to high-voltage lines. It is well known that high voltage means low current, low current in its turn results in reduced heating losses in electrical wires. It is dangerous, however, to use power at very high voltages for anything but transmission and distribution. For that reason, the voltage is always reduced again before the power is made use of. Lasers. Soviet scientists are successfully developing quantum generators, called lasers, for emitting light amplitude radio waves. Theoretical calculations have shown that lasers are very likely to transform the energy of light radio waves into electrical energy with an efficiency amounting to about 100 per cent. It means that electrical power might be transmitted over considerable distances with negligible losses and what is very important without the use of transmission lines.
THE DISCOVERY OF ELECTRO-MAGNETIC INDUCTION
It is at this important juncture in the history of electrical research that we see 56 the first, shy attempts to make this force of Nature do some work. Now we are concerned with the development of electricity for the transmission of energy. One day in 1819 a Danish physicist, Hans Christian Oersted, was lecturing at the University of Kiel, which was then a Danish town. Demonstrating a galvanic battery, he held up a wire leading from it when it suddenly slipped out of his hand and fell on the table across a marine's compass that happened to be there. As he picked up the wire again he noticed to his astonishment that the needle of the compass no longer pointed north, but had swung completely out of position. He switched the current off, and the needle pointed north again. For a few months he thought over this incident, and eventually wrote a short report on it. No one could have been more surprised than Oersted at the extraordinary impact which his discovery made on physicists all over Europe and America. At last the longsought connection between electricity and magnetism had been found! Yet neither Oersted nor his colleagues could forsee the importance of this phenomenon, for it is the connection between electricity and magnetism on which the entire practical use of electricity in our time is foundedy What was it that Oersted had discovered? Nothing more than that an electrically charged conductor, such as the wire leading from a battery, is the centre of a magnetic 'field', and this has the effect of turning a magnetic needle at a right angle with the direction in which the current is flowing; not quite at a right angle, though, because the magnetism of the earth also influences the needle. Now the physicists had a reliable means of measuring the strength of a weak electric current flowing through a conductor; the galvanoscope, or galvanometer, is such a simple instrument consisting of a few wire loops and a magnetic needle whose deflection indicates the strength of the current. Prompted by the research work of Andre-Marie Ampere, the great French physicist whose name has become a household word as the unit of the electric current, the Englishman Sturgeon experimented with ordinary, non-magnetized iron. He found that any piece of soft iron could be turned into a temporary magnet by putting it in the centre of a coil of insulated wire and making an electric current flow through the coil. As soon and as long as the current was turned on the iron was magnetic, but it ceased to be a magnet when there was no more current. Sturgeon built the first large electro-magnet, and. with this achievement there began the development of the electrical telegraph and later the telephone. But there was yet another, and perhaps even more important, development which began with the electro-magnet. Michael Faraday repeated the experiments of Oersted, Sturgeon, and Ampere. His brilliant mind conceived this idea: if electricity could produce magnetism, perhaps magnetism could produce electricity! But how? For a long time he searched in vain for an answer. Every time he went for a walk in one of London's parks he carried a little coil and a piece of iron in his pocket, taking them out now and then1 to look at them. It was on such a walk that he found the solution. Suddenly, one day in 1830, in the midst of Green Park (so the story goes), he knew it: the way to produce electricity by magnetism was – by motion. He hurried to his laboratory and put his theory to the test. It was correct. 57 A stationary magnet does not produce electricity. But when a magnet is pushed into a wire coil current begins to flow in the coil; when the magnet is pulled out again, the current flows in the opposite direction. This phenomenon, confirms the basic fact that the electric current cannot be produced out of nothing–some work must be done to produce it. Electricity is only a form of energy; it is not a 'prime mover' in itself. What Faraday had discovered was the technique of electro-magnetic induction, on which the whole edifice of electrical engineering rests. He soon found that there were various ways of transforming motion into electric current. Instead of moving the magnet in and out of the wire coil you can move the coil towards and away from the magnet; or you can generate electricity by changing the strength of stationary magnet; or you can produce a current in one of two coils by moving them towards and away from each other while a current is flowing in the second. Faraday then substituted a magnet for the second coil and observed the same effect. Using two coils wound on separate sections of a closed iron ring, with one coil connected to a galvanometer and the other to a battery, he noticed that when the circuit of the second coil was closed the galvanometer needle pointed first in one direction and then returned to its zero position. When he interrupted the battery circuit, the galvanometer jerked into the opposite direction. Eventually, he made a 12- inch-wide copper disc which he rotated between the poles of a strong horse-shoe magnet; the electric current which was generated in the copper disc could be obtained from springs or wire brushes touching the edge and axis of the disc. Thus Faraday demonstrated quite a number of ways in which motion could be translated into electricity. His fellow-scientists at the Royal Institution and in other countries were amazed and impressed – yet neither he nor they proceeded to make practical use of his discoveries, and nearly forty years went by before the first electric generator, or dynamo, was built. Meanwhile, fundamental research into the manifold problems of electricity continued. In America, Joseph Henry, professor of mathematics and natural science, also starting from Oersted's and Sturgeon's observations, used the action of the electric current upon a magnet to build the first primitive electric motor in 1829. At about the same time, Georg Simon Ohm, a German school-teacher found the important law of electric resistance: that the amount of current in a wire circuit decreases with the length of the wire, which acts as resistance. Ohm's excellent research work remained almost unnoticed during his lifetime, and he died before his name was accepted as that of the unit of electrical resistance.
DIRECT-CURRENT METERS
Functions of a Direct Current Meter.– A direct current meter is an instrument intended for the measurement of electrical quantity in a direct current circuit. There are two main classes of direct current meters, ampere-hour meters and watthour meters. An ampere-hour meter measures the product of the current in amperes flowing in a circuit and the time in hours during which the flow is maintained. A watt-hour meter measures the product of the power in watts and the time in hours during which the flow of power is maintained. Direct Current Ampere-hour Meters.– Ampere-hour meters are used by electrical undertakings for measuring the supply of electricity to domestic and industrial, consumers. These undertakings are under a statutary obligation to maintain the voltage at consumers' terminals at a declared value within close limits; assuming that the supply voltage is maintained at the declared value, an ampere-hour meter can be calibrated to register in terms of kilowatt-hours at this voltage. This principle is accepted as satisfactory in most countries where the voltage at consumers' terminals is maintained within narrow limits of the declared voltage, and since direct current ampere-hour meters are, in general, more reliable and less costly than direct current watt-hour meters the practice has much in its favour. In addition to the foregoing, ampere-hour meters are used for measuring the current consumption in battery charging, electro-deposition and other electrolytic or industrial processes and in some instances they exercise a controlling function over these operations. Many types of ampere-hour meter have been manufactured in the past, the most important being electrolytic meters and motor meters. Theoretically the former are capable of very accurate registration but in practice the working results are not so good as with motor meters, and the latter are preferred by most supply authorities.
ELECTRIC CIRCUIT
The electric circuit is the subject to be dealt with in the present article. But what does the above term really mean? We know the circuit to be a complete path which carries the current from the source of supply to the load and then carries it again from the load back to the source. The purpose of the electrical source is to produce the necessary electromotive force required for the flow of current through the circuit* The path along which the electrons travel must be complete otherwise no electric power can be supplied from the source to the load. Thus we close the circuit 32 when we switch on our electric lamp. If the circuit is broken or, as we generally say "opened" anywhere, the current is known to stop everywhere. Hence, we break the circuit when we switch off our electrical devices. Generally speaking, the current may pass through solid conductors, liquids, gases, vacuum, or any combination of these. It may flow in turn over transmission lines from the power-stations through transformers, cables and switches, through lamps, heaters, motors and so on. There are various kinds of electric circuits such as: open circuits, closed circuits, series circuits, parallel circuits and short circuits. To understand the difference between the following circuit connections is not difficult at all. When electrical devices are connected so that the current flows from one device to another, they are said to be connected in series. Under such conditions the current flow is the same in all parts of the circuit, as there is only a single path along which it may flow. The electrical bell circuit is considered to be a typical example of a series circuit. The parallel circuit provides two or more paths for the passage of current. The circuit is divided in such a way that part of the current flows through one path, and part through another. The lamps in your room and your house are generally connected in parallel. Now we shall turn our attention to the short circuit sometimes called "the short". The short circuit is produced when the current is allowed to return to the source of supply without control and without doing the work that we want it to do. The short circuit often results from cable fault or wire fault. Under certain conditions, the short may cause fire because the current flows where it was not supposed to flow. If the current flow is too great a fuse is to be used as a safety device to stop the current flow. The fuse must be placed in every circuit where there is a danger of overloading the line. Then all the current to be sent will pass through the fuse. When a short circuit or an overload causes more current to flow than the carrying capacity of the wire, the wire becomes hot and sets fire to the insulation. If the flow of current is greater than the carrying capacity of the fuse, the fuse melts and opens the circuit. A simple electric circuit is illustrated in Fig. 3. In (his figure a 4-cell battery has been used, the switch being in an open position. If the switch is in a closed position, the current will flow around the circuit in the direction shown by the arrows.
Список используемой литературы:
1. Бахчисарайцева М.Э., Каширина В.А., Антипова А.Ф. Пособие по английскому языку для старших курсов энергетических вузов. – М.: Высшая школа, 1983.
2. Иванова К. А., Английский язык для студентов-электротехников. – Ленинград, 1983.