220kv变电站设计外文翻译

General Requirements to Construction of SubstationSubstations are a vital element in a power supply system of industrial enterprises．They serve to receive ，convert and distribute electric energy .Depending on power and purpose ,the substations are divided into central distribution substations for a voltage of 110-500kV;main step-down substations for110-220/6-10-35kV;deep entrance substations for 110-330/6-10Kv;distribution substations for 6-10Kv;shop transformer substations for 6-10/0.38-0.66kV.At the main step-down substations, the energy received from the power source is transformed from 110-220kV usually to 6-10kV(sometimes 35kV) which is distributed among substations of the enterprise and is fed to high-voltage services.Central distribution substations receive energy from power systems and distribute it (without or with partial transformation) via aerial and cable lines of deep entrances at a voltage of 110-220kV over the enterprise territory .Central distribution substation differs from the main distribution substation in a higher power and in that bulk of its power is at a voltage of 110-220kV;it features simplified switching circuits at primary voltage; it is fed from the power to an individual object or region .Low-and medium-power shop substations transform energy from 6-10kV to a secondary voltage of 380/220 or 660/380.Step-up transformer substations are used at power plants for transformation of energy produced by the generators to a higher voltage which decreases losses at a long-distance transmission .Converter substations are intended to convert AC to DC (sometimes vice versa) and to convert energy of one frequency to another .Converter substations with semiconductor rectifiers are convert energy of one frequency to another .Converter substations with semiconductor rectifiers are most economic. Distribution substations for 6-10kV are fed primarily from main distribution substations (sometimes from central distribution substations).With a system of dividing substations for 110-220kV, the functions of a switch-gear are accomplishedby switch-gears for 6-10kV at deep entrance substations.Depending on location of substations their switch-gear may be outdoor or indoor. The feed and output lines at 6-10kV substations are mainly of the cable type .at 35-220kV substations of the aerial type .When erecting and wiring the substations ,major attention is given to reliable and economic power supply of a given production.Substations are erected by industrial methods with the use of large blocks and assemblies prepared at the site shops of electric engineering organizations and factories of electrical engineering industry .Substations are usually designed for operation without continuous attendance of the duty personnel but with the use of elementary automatic and signaling devices.When constructing the structural part of a substation .it is advisable to use light-weight industrial structures and elements (panels ,floors ,etc.) made of bent sections .These elements are pre-made outside the erection zone and are only assembled at site .This considerably cuts the terms and cost of construction.Basic circuitry concepts of substations are chosen when designing a powersupply system of the enterprise .Substations feature primary voltage entrances .transformers and output cable lines or current conductors of secondary voltage .Substations are mounted from equipment and elements described below .The number of possible combinations of equipment and elements is very great .Whenelaborating a substation circuitry ,it is necessary to strive for maximum simplification and minimizing the number of switching devices .Such substations are more reliable and economic .Circuitry is simplified by using automatic reclosure or automatic change over to reserve facility which allows rapid and faultless redundancy of individual elements and using equipment.When designing transformer substations of industrial enterprises for all voltages , the following basic considerations are taken into account:1. Preferable employment of a single-bus system with using two-bus systems only to ensure a reliable and economic power supply;2. Wide use of unitized constructions and busless substations;3.Substantiated employment of automatics and telemetry ;if the substation design does not envisage the use of automatics or telemetry ,the circuitry is so arranged as to allow for adding such equipment in future without excessive investments and re-work.e of simple and cheap devices-isolating switches ,short-circuiting switches ,load-breaking isolators ,fuses ,with due regard for their switching capacity may drastically cut the need for expensive and critical oil ,vacuum ,solenoid and air switches .Substation and switch-gear circuitries are so made that using the equipment of each production line is fed from individual transformers ,assemblies ,the lines to allow their disconnection simultaneously with mechanisms without disrupting operation of adjacent production flows.When elaborating circuitry of a substation, the most vital task is to properly choose and arrange switching devices(switches ,isolators ,current limiters ,arresters ,high-voltage fuses).The decision depends on the purpose ,power and significance of the substation.Many years ago, scientists had very vague ideas about electricity. Many of them thought of it as a sort of fluid that flowed through wires as water flows through pipes, but they could not understand what made it flow. Many of them felt that electricity was made up of tiny particles of some kind ,but trying to separate electricity into individual particles baffled them.Then, the great American scientist Millikan, in 1909,astounded the scientific world by actually weighing a single particle of electricity and calculating its electric charge. This was probably one of the most delicate weighing jobs ever done by man,for a single electric particle weighs only about half of a millionth of a pound. To make up a pound it would take more of those particles than there are drops of water in the Atlantic Ocean.They are no strangers to us, these electric particles, for we know them as electrons. When large numbers of electrons break away from their atoms and move through a wire,we describe this action by saying that electricity is flowing through the wire.Yes,the electrical fluid that early scientists talked about is nothing more than electrical flowing along a wire.But how can individual electrons be made to break away from atoms? And how can these free electrons be made to along a wire? The answer to the first question lies in the structure of the atoms themselves. Some atoms are so constructed that they lose electrons easily. An atom of copper, for example ,is continually losing an electron, regaining it(or another electron),and losing it again. A copper atom normally has 29 electrons, arranged in four different orbits about its nucleus. The inside orbit has 2 electrons. The next larger orbit has 8.The third orbit is packed with 18 electrons . And the outside orbit has only one electron.It is this outside electron that the copper atom is continually losing, for it is not very closely tied to the atom. It wanders off, is replaced by another free-roving electron, and then this second electron also wanders away.Consequently,in a copper wire free electrons are floating around in all directions among the copper atoms.Thus, even through the copper wire looks quite motionless to your ordinary eye, there is a great deal of activity going on inside it. If the wire were carrying electricity to an electric light or to some other electrical device, the electrons would not be moving around at random. Instead, many of them would be rushing in the same direction-from one end of the wire to the other.This brings us to the second question .How can free electrons be made to move along a wire? Well ,men have found several ways to do that .One way is chemical. V olta,s voltaic pile,or battery, is a chemical device that makes electricity(or electrons)flow in wires. Another way is magnetic. Faraday and Henry discovered how magnets could be used to make electricity flow in a wire.MagnetsAlmost everyone has seen horseshoe magnets-so called because they are shaped like horseshoes. Probably you have experimented with a magnet, and noticed how it will pick up tacks and nails, or other small iron objects. Men have known about magnets for thousands of years.Several thousand years ago, according to legend, a shepherd named Magnes lived on the island of Crete, in the Mediterranean Sea .He had a shepherds crook tipped with iron. One day he found an oddly shaped black stone that stuck to this ironter, when many other such stones were found, they were called magnets(after Magnets).These were natural magnets.In recent times men have learned how to make magnets out of iron. More important still, they have discovered how to use magnets to push electrons through wires-that is, how to make electricity flow. Before we discuss this, there arecertain characteristics of magnets that we should know about.If a piece of glass is laid on top of a horse- shoes magnet, and if iron filings are then sprink ledon the glass, the filings will arrange themselves into lines. If this same thing is trid with a bar magnet(a horseshoe magnet straightened out),the lines can be seen more easily. These experiments demonstrate what scientists call magnetic lines of force. Magnets, they explain, work through lines of force that ext- end between the two ends of the magnet. But electrons seem to have magnetic lines of force around them, too.This can be proved by sticking a wire through a piece ofcard board, sprinkling iron filings on the cardboard, and connecting a battery to the wire. The filings will tend to form rings around the wire,as a result of the magnetism of the moving electrons(or electricity).So we can see that there is arelationship between moving electrons and magnetism, Magnetism results from the movement of electrons.Of course, electrons are not really flowing in the bar magnet, but they are in motion, circling the nuclei of the iron atoms. However, in the magnet, circling thelined up in such a way that their electrons are circling in the same direction. Perhaps a good comparison might be a great number of boys whirling balls onstrings in a clockwise direction around their heads.。