1、外文文献 一 General Requirements to Construction of Substation Substations 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 substatio
2、ns 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
3、 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
4、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 f
5、rom 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
6、 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 substation
7、s 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 accomplished by switch
8、-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 a
9、ttention 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
10、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
11、 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 vo
12、ltage 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 t
13、o 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 an
14、d 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 us
15、e 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 r
16、e-work. 4.Use 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
17、 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 t
18、ask 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 a
19、s 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 America
20、n 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
21、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
