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1、电力专业英语电力系统中的高电压技术你现在浏览的是第一页，共40页TopicsInsulationGroundingOvervoltageLightning Shielding你现在浏览的是第二页，共40页Insulation 1Insulation is required to keep electrical conductors separated from each other and from other nearby objects.The choice of material is dictated by the requirements of the particular appl
2、ication and by cost.你现在浏览的是第三页，共40页Insulation 2The coils of generators and motors may be insulated with various tapes.The insulation on power transformer windings is commonly paper tape and pressboard operated under oil.你现在浏览的是第四页，共40页Insulation 3Overhead lines are supported on porcelain insulators.
3、Between the supports air serves as insulation.Porcelain is chosen because of its resistance to deterioration when exposed to the weather,its high dielectric strength,and its ability to wash clean by rain.你现在浏览的是第五页，共40页Insulation 4The cost of equipment and the system as a whole is closely related to
4、 the insulation level which has been adopted for the network.The choice of insulation level should take into account both the probability of occurrence and the severity of stress that the system may be subjected to.你现在浏览的是第六页，共40页500KV开关场 switchyard你现在浏览的是第七页，共40页500KV变压器 transformer你现在浏览的是第八页，共40页2
5、20KV开关场 switchyard你现在浏览的是第九页，共40页220KV开关场 switchyard你现在浏览的是第十页，共40页电力电缆 power cables你现在浏览的是第十一页，共40页电力电缆 power cable你现在浏览的是第十二页，共40页钢芯铝绞线 aluminum conductor steel reinforced 你现在浏览的是第十三页，共40页架空输电线overhead transmission line你现在浏览的是第十四页，共40页架空输电线overhead transmission line你现在浏览的是第十五页，共40页Insulation Coord
6、inationElectric systems insulation designers have two options available to them:choose insulation levels for components that would withstand over voltages,devise protective devices that could limit over voltages there.你现在浏览的是第十六页，共40页GroundingGrounding is defined as a conducting connection,whether i
7、ntentional or accidental,by which an electric circuit or equipment is connected to the earth,or to some conducting body of relatively large extent that serves in place of the earth.你现在浏览的是第十七页，共40页GroundingThe most important reason for grounding is safety.Two important aspects to grounding requireme
8、nts with respect to safety and one with respect to power quality are follows:Personnel safety To assure protective device operation Noise control你现在浏览的是第十八页，共40页接地网施工 construction of ground grid你现在浏览的是第十九页，共40页接地网施工 construction of ground grid你现在浏览的是第二十页，共40页OvervoltagesThe overvoltages can be divid
9、ed into external overvoltages and internal overvoltages according to the locations of sources.External overvoltages are generated by sources that external to the power system network.Their magnitude is essentially independent of the system.你现在浏览的是第二十一页，共40页External OvervoltagesLightning overvoltages
10、 are characterized by very high peak currents and relatively low energy content.They are responsible for nearly half of all short circuits on lines in systems of 300kv and above.Up to 300kv the system insulation has to be designed primarily to withstand lightning surges.你现在浏览的是第二十二页，共40页Internal Ove
11、rvoltagesInternal overvoltages are principally determined by the system configuration and its parameters.They are mainly due to switching operations and following fault conditions.According to their duration,which ranges from hundreds of microseconds to several seconds,three main categories of inter
12、nal overvoltages can be defined:你现在浏览的是第二十三页，共40页Internal Overvoltages1 Transient Switching Surges.2 Temporary Overvoltages.3.Steady-state Overvoltages.你现在浏览的是第二十四页，共40页Lightning StrokesDuring stormy weather,by a process not yet fully understood,a charge separation takes place inside clouds,so that
13、positive charges move to the upper part of the cloud while negative charges stay below.This transfer of electric charge sets up an electric field within the cloud.你现在浏览的是第二十五页，共40页Lightning StrokesThe negative charge at the base of the cloud repels the free electrons on the ground below.Consequently
14、,the surface of the ground becomes positively charged,by induction.你现在浏览的是第二十六页，共40页Lightning StrokesAs more and more positive charges are move upward within the cloud,the electric field below the cloud becomes more and more intense.Ultimately,it reaches the critical ionization level where air begin
15、s to breakdown.Ionization takes places first at the tips of high buildings,such as church spires,and the top of high trees.你现在浏览的是第二十七页，共40页Lighting Stroke你现在浏览的是第二十八页，共40页Lighting Stroke你现在浏览的是第二十九页，共40页Lighting Stroke你现在浏览的是第三十页，共40页Lighting Strokes 你现在浏览的是第三十一页，共40页Lighting Conductors 你现在浏览的是第三十二
16、页，共40页Lighting Conductors 你现在浏览的是第三十三页，共40页Lightning Shielding of Transmission LinesWhen lightning makes a direct hit on a transmission line,it deposits a large electric charge,producing an enormous overvoltage between the line and the ground.The dielectric strength of air is immediately exceeded an
17、d a flashover occurs.你现在浏览的是第三十四页，共40页Lightning Shielding of Transmission LinesThe arc between the line and the ground produces a highly ionized path which behaves like a a conducting short-circuit.Consequently,the normal AC line voltage immediately delivers a large AC current that follows the ioniz
18、ed path.This follow-through current may sustain the arc until the circuit breakers open at the end of line.你现在浏览的是第三十五页，共40页Lightning Shielding of Transmission LinesDirect hits on a transmission line are rare.More often,lightning will strike the overhead ground wire that shields the line.In the latt
19、er case,a local charge shill accumulates on the line,producing a very high local overvoltage.你现在浏览的是第三十六页，共40页Overhead Ground Wires你现在浏览的是第三十七页，共40页Overhead Ground Wires你现在浏览的是第三十八页，共40页Lightning Arresters你现在浏览的是第三十九页，共40页Travelling WavesThe concentrated charge immediately divides into two waves that swiftly move in opposite directions at close to the speed of light.The height of the impulse wave represents the magnitude of the surge voltage that exists from point to point between the line and the ground.The peak voltage may attain one or two million volts.你现在浏览的是第四十页，共40页