接地线毕业论文外文翻译.doc

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1、附录1 英文翻译网址 http:/en.wikipedia.org/wiki/Ground_(electricity)接地线从维基百科,自由的百科全书在澳大利亚的一个家里,一个典型接地电极 (左边的灰色管),由导电杆组成的钉钉在地里, 许多电气规范规定，特别是接地线必须是一个特定的颜色，以防止接线错误在电气工程中,可以以地面或地球(象征:) 作为参考点测量电路的电压,一个地上常见的电流返回的路径,或直接物理地连接到地球。电路连接到地面(地球) 可能有几个原因。在许多能源设备中,暴露的金属零件和电源供电设备部件连接到地面,防止用户因电气绝缘而接触危险电压, 如果电气绝缘失败可以防止用户接触危险电

2、压。在处理易燃产品或静电感应设备时连接地面可以限制静电的积聚。在一些电报和输电线路上，地球本身可以作为一个导体的电路，节省了安装一个单独的导线回路的成本（见单独大地导线回路）。为了便于测量，其他电位可以以地球作为的一个合理恒电位参考点来测量。一个电气接地系统应该有一个适当的电流承载能力作为充分的零电压参考水平。在电子电路理论中,“地面”通常是理想化作为一个无源电荷或水槽,可以吸收无限数量的电流而不改变其电势。在一个真正的接地有很大的电阻时，电势零电位的近似不再有效。长久杂散电压或者地面电位升高将会发生，这可能会产生噪音信号，如果足够大，就会产生触电危险。在电气以及便携式电子设备中,接地一词的使

3、用时如此的普通.例如,电话, 媒体播放器以及在汽车电路中,但是它们可能是口语的接地 ,而没有任何实际连接到地球。这通常是一个大导体连接到电源的一侧(如地平面在印刷电路板上), 这是许多不同的组件的电路常见的返回路径。 目录1历史2无线电通讯3交流电力线路安装4电力传输5电子 5.1电路地面与地球 5.2 分离低信号地从嘈杂的地面6防雷系统7接地系统8压焊9地面垫(地球)10隔离11典型的工业接地系统12另请参阅13笔记14引用15外部链接历史长途电磁电报系统从1820年开始引文需要使用两个或两个以上的电线来传送信号并返回电流, 后来发现,可能由德国科学家卡尔Steinheil在1836 - 1

4、837年8月发现地面可以作为返回路径完成电路循环,使返回导线成为不必要的东西.然而,这个系统有问题,以西部联合电报公司建于1861年连接圣约瑟夫,密苏里州和萨克拉门托,加利福尼亚州的跨越大陆电报线为例。在干燥的天气，地面连接经常产生高电阻，需要将水倒在接地棒上使电报正常工作或电话铃声报警。 后来,当电话开始取代电报,结果发现由电力系统, 电气铁路、其他电话电报电路,和天然来源包括闪电引起的地面电流,导致产生不可接受的干扰音频信号,这使得二线或金属电路系统于1883年左右重新被引入.无线电通信一个电气连接地球可以为某些类型的天线射频信号用作为潜在的参考电位。直接与地面接触的部分“地球电极” 连接

5、.可以简单到一根金属棒或桩插入到地球,或连接到埋在地里的金属水管(这水管必须导电)。因为高频信号能够流向地球由于容性的影响,电流容量对地球电容信号是一个重要的影响因素。正因为如此,一个复杂的系统可以有效的通过埋电线杆和电线。理想的接地信号保持在一个固定的值(零)无论多少电流流入地里或流出地里。低阻抗的电极与大地连接决定了信号频率的质量,而质量的提高是通过增加电极的表面积与地面接触,使用几个连接接地棒, 增加它的深度驱动,增加土壤的水分含量,提高土壤的导电矿物含量,增加土地面积覆盖的接地系统。 在一些典型的发射天线系统中，VLF,LF,MF和低SW范围必须要有良好的接地来有效运作。例如, 垂直单

6、级天线需要一个地平面,通常由一个互联网络电线径向运行,其远离基地天线的距离大约等于天线的高度。有时一个秤锤作为地面飞机,支持地面。交流电力线路安装在一些主要电源（交流电源）布线安装中，这个术语通常指的是如下三种不同的接地导体或导体系统。接地导体设备提供的电气连接在非载流金属设备和地球之间。据美国国家电气规范(NEC)说明,这样做的原因是为了限制由闪电，电压线浪涌接触高电压电线路而强加给导线电压造成线路拥塞,这种接地导体设备也常常用来连接设施导体 (见下文)。设备连接导体提供一个低阻抗路径在非载流金属设备部分和导体的电气系统的一个来源之间,因此,如果一部分由于任何原因变得能量充足,例如磨损或损坏

7、导线操作,断路器会发生短路操作或熔断器断开损坏电路。注意,地球本身在故障排除过程中没有这个作用 .因为当前它必须回到它的源头,而不是认为地球有时引文需要(见基尔霍夫电流定律)。通过(连接)与所有接触的非流动携带金属物品在一起,他们应该保持有同样的潜力从而减少冲击的机会。一个可以接触不同的金属系统这在浴室是特别重要的, 如供应和排水的管道和设备框架。设备焊接导线通常也用于设备接地导体(见上图)。接地电极导线连接一条腿的电气系统的一个或多个接地电极。这就是所谓的“系统接地”.大多数系统都必须接地。美国NEC和英国BS 7671列表需要接地的系统。接地电极导线连接到的电力系统是“中性线”的腿。接地极

8、导体通常是结合管道结构和大型结构钢。根据NEC,接地的电气系统的目的是限制地球施加的电压和接触高电压线路造成雷击事件,并稳定地球电压在正常操作值之间。在过去,供水管道经常被用作地面电极,但这是被禁止的,而塑料管道很受欢迎。这种类型的地面适用于无线电天线和防雷系统。永久性安装的电气设备通常也有永久连接大地的接地导体。便携式的金属电子设备的可能通过连接插头的引脚连接到地面（见家用交流电源插头和插座）。功率大小的接地导体也通常是由当地或国家的布线法规规定的。电力运输在单线接地回路(SWER)交流电气配电系统中,只使用一个单一的高电压导体对电网进行保存，从而节省成本.同时路径由电流通过交流返回地球。该

9、系统主要用于农村地区,电流接大地后不会造成危害。一些高压直流(HVDC)输电系统使用地面作为第二个导体。尤其以海底电缆常见,海水是良好的导体。埋接地电极用于连接到地球。这些电极必须认真选择,从而防止网站对地下结构造成电化学腐蚀。设计时要特别注意电力变电站地电位的上升。当非常大的故障电流注入大地,周围地区的注入电流可能上升到一个非常大的限制点。这是由于有限的电导率层土壤在地球引起的.这个梯度电压(电压变化在一个距离)可能是如此之高,以至于在地上的两个点可能有显著不同的电位,从而危害任何一个站在地上的人。管道，轨道，或通信导线进入变电站接地电位，可以看到不同的内部和外部的变电站，创造了一个危险的接

10、触电压。电子技术地面标志信号场作为回报信号和电源路径（在超低电压，低于约50 V）的设备，并对设备间的信号线和设备之间互连。许多电子产品设计功能单一的回报,作为参考信号。电源和信号地经常获得连接，通常通过设备的金属外壳。 电路接地与地球 电压是一个微分数量。测量一个点的电压,必须选择一个参考点来衡量。这种常见的参考点选择“地面”,它被认为零电压点。这个信号不会连接到地面。一个系统没有连接到另一个电路或地球(虽然可能仍然是交流耦合)通常被称为一个浮动的地面。从嘈杂的地面分离低信号在电视台、录音棚和其他设施中,声音质量是至关重要的, 一个特殊的信号称为“技术接地”(或“接地技术”,“特殊的地球”和

11、“音频地球”)通常被安装,以防止地面循环。这基本上是同样的事情作为一个交流电源,但不允许任何通用设备接地线连接,因为它们可能携带电子干扰。例如在录音室只有音频设备连接到地面技术。在大多数情况下,工作室的金属设备机架都一起加入了沉重的铜电缆(或扁平的铜管或汇流)和类似的连接技术。没有通用底盘接地设备的放置于货架上要非常小心,作为一个交流接地技术会破坏其有效性。对于特别要求的应用程序,主要的地面技术可能由一个沉重的铜管组成,如果有必要可以通过几个具体的地板安装钻井,这样,所有的技术接地可能通过最短路径在地下室里连接到接地杆。防雷系统汇流用于大地电流电路的接地导体。防雷系统的设计是为了通过连接到接地

12、系统减少雷电的影响，广泛地提供了一个大面积的连接与地球。所需的大面积消耗了大量电流, 从而雷击导体多余的热量不会造成系统崩溃。由于闪电脉冲频率成分的能量非常高,照明保护接地系统倾向于使用短直的导体,以减少自身电感和皮肤的效果。接地系统主要文章:接地系统。在电力供应系统中，一个接地系统定义了电气的潜在导体相对于地球的导电层.接地系统的选择影响供电的安全性和电磁兼容性。注意, 不同国家之间规定接地系统的差别很大。 功能性接地是一个目的,而非防止提供电击。与保护接地连接相比,功能性接地可能携带电流在一个设备上正常运行。功能连接地球可能需要通过设备如浪涌抑制和电磁兼容过滤器,某些类型的天线和各种测量仪

13、器。一般地球保护也被用作一个功能,虽然在某些情况下,这需要护理。连接主要文章: 电气连接严格说来,条款接地或接地是指地面/地球的电气连接。特意接接地连接的金属物品不是设计来进行电力的转移。这使所有物品保持相同的电势免受电击。接地连接可以把他们的电荷带到地面使他们免受电击。接地网主要文章:接地网接地网垫或接地垫垫是一个平面，通常用在静电敏感器件上。它通常是由导电塑料或金属网覆盖衬底组成电气连接到地面（地球）。这有助于排出任何一个工人已经建立了的静电, 以及任何工具或接触组件上的产生的静电荷转移到垫子上。它最常用于电脑维修。接地网还用于燃料卡车和油轮，否则不与地面绝缘,他们仅仅用轮胎接触地面和空气

14、,显然静电放电能力转移操作期间是不可取的。同样,在飞机加油、地面(地球)电缆连接油轮(卡车或飞机)来消除电荷在燃料转移前。在电子变电站接地（接地）垫是安装在一种网状导电材料的地方，一个人将操作开关或其他设备,它是结合当地的金属支撑结构的开关手柄，使操作者不会暴露于变电站高电压差的故障中。 隔离隔离是一个失败的机制接地。它经常被用于低功耗消费设备,当电子工程师,业余爱好者,或者修理一个正在工作的电路,他通常会使用电力线路电压进行操作。隔离可以通过简单的1:1线比与常规电力服务设备之间轮流同等数量的变压器来实现，但是适用于任何两个类型的变压器使用两个或者两个以上的线圈将使彼此隔离一个孤立的设备,触

15、摸一个供电导线不会引起严重的冲击,因为通过地面没有路径回到另一个导体。然而, 如果两极的变压器是由裸露的皮肤接触仍有可能发生冲击和电刑。之前建议修理工“工作用一只手 “避免同时碰两部分的测试设备,从而防止电路交叉通过胸部和心脏造成节律中断/导致心脏骤停。通常将每一个交流电源线路变压器作为隔离变压器,上升下降,每一步都有可能形成一个隔离电路。然而,这种隔离将防止设备保险丝短路接地导体。隔离可以被每个总有一条腿接地的变压器击穿,两边的输入和输出变压器线圈。电线通常一线一杆,以确保电流均衡从南极到北极如果短地发生。过去,接地设备设计与内部隔离在某种程度上,允许简单的在地面被骗子插头断开并无明显的问题

16、(一个危险的做法,因为产生的漂浮设备的安全依赖于电力变压器的绝缘)。然而现代电器通常包括电源输入模块与深思熟虑的设计交流电源线路和底盘之间的电容耦合,抑制电磁干扰。这会从地面的电线导致一个重大的电流泄漏。如果地面是由一个骗子插头断开或偶然断开, 即使没有任何设备故障,也有可能由此产生的泄漏电流引起轻微的冲击, 在医疗环境中，即使很小的泄漏电流也是一个重要的问题,意外断开的地面可以使这些水流进入人体的敏感部分。因此,医疗电源设计为低电容。二类电器和电源(如手机充电器)不提供任何接地,并被设计成分离的输出输入。由加倍隔离安全保障,因此, 两次失败的绝缘必定引起认他休克。工业接地系统的类型:直接接地

17、系统。低阻接地系统。高阻接地(HRG)系统。 低电阻接地系统使用一个中立的接地电阻限制故障电流至25A或更高。低电阻接地系统将有一个时间评级(例如10秒),表示电阻器多长时间可以携带过热前的故障电流。接地故障保护继电器必须跳闸断路器在过热时保护电路 高阻接地(HRG)系统使用的是限制故障电流至25A或更少。他们有一个连续的评级，并设计与操作单相接地故障。这意味着系统将不会立即履行第一接地故障。如果第二个接地故障发生时,一个接地故障保护继电器必须跳闸断路器来保护电路。HRG系统传感电阻是用来持续监测系统连续性的。如果一个开路的检测（例如，由于对NgR破碎的焊缝），监测装置将通过感应电阻和跳闸断路

18、器来检测电压。没有感应电阻器,系统可以继续保护没有接地 (因为一个开路条件会掩盖了接地故障)和瞬态过电压可能发生的冲击。附录2 英文原文Ground (electricity)From Wikipedia, the free encyclopediaA typical earthing electrode(left of gray pipe), consisting of a conductive rod driven into the ground, at a home inAustralia.Manyelectrical codesspecify that earthing wires m

19、ust be a certain color, to prevent wiring errors.Inelectrical engineering,groundorearth(symbol:) can refer to the reference point in anelectrical circuitfrom which voltages are measured, a common return path forelectric current, or a direct physical connection to theEarth.Electrical circuits may be

20、connected to ground (earth) for several reasons. Inmainspowered equipment, exposed metal parts are connected to ground to prevent user contact with dangerous voltage ifelectrical insulationfails. Connections to ground limit the build-up ofstatic electricitywhen handling flammable products orelectros

21、tatic-sensitive devices.In sometelegraphandpower transmissioncircuits, the earth itself can be used as oneconductorof the circuit, saving the cost of installing a separate return conductor (seesingle-wire earth return).For measurement purposes, the Earth serves as a (reasonably) constant potential r

22、eference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability to serve as anadequate zero-voltage reference level. Inelectronic circuittheory, a ground is usually idealized as an infinitesource or sinkfor charge, which can

23、 absorb an unlimited amount of current without changing its potential. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid.Stray voltagesorearth potential riseeffects will occur, which may create noise in signals or if large enough will

24、 produce an electric shock hazard.The use of the term ground (or earth) is so common in electrical and electronics applications that circuits inportable electronic devicessuch ascell phonesandmedia playersas well as circuits invehiclesmay be spoken of as having a ground connection without any actual

25、 connection to the Earth. This is usually a large conductor attached to one side of thepower supply(such as the ground plane on aprinted circuit board) which serves as the common return path for current from many different components in the circuit.Contentshide 1History 2Radio communications 3AC pow

26、er wiring installations 4Power transmission 5Electronicso 5.1Circuit ground versus eartho 5.2Separating low signal ground from a noisy ground 6Lightning protection systems 7Earthing system 8Bonding 9Ground (earth) mat 10Isolation 11Types of Industrial Grounding Systems 12See also 13Notes 14Reference

27、s 15External linksHistoryeditLong-distance electromagnetic telegraph systems from 1820 onwardscitation neededused two or more wires to carry the signal and return currents. It was then discovered, probably by the German scientistCarl August Steinheilin 18361837,1that the ground could be used as the

28、return path to complete the circuit, making the return wire unnecessary. However, there were problems with this system, exemplified by the transcontinental telegraph line constructed in 1861 by the Western Union Company betweenSaint Joseph, Missouri, andSacramento, California. During dry weather, th

29、e ground connection often developed a high resistance, requiring water to be poured on theground rodto enable the telegraph to work or phones to ring.Later, when telephony began to replace telegraphy, it was found that the currents in the earth induced by power systems, electrical railways, other te

30、lephone and telegraph circuits, and natural sources including lightning caused unacceptable interference to the audio signals, and the two-wire or metallic circuit system was reintroduced around 1883.2Radio communicationseditAnelectrical connectionto earth can be used as a reference potential forrad

31、io frequencysignals for certain kinds ofantennas. The part directly in contact with the earth - the earth electrode - can be as simple as a metal rod or stake driven into the earth, or a connection to buried metal water piping (the pipe must be conductive). Because high frequency signals can flow to

32、 earth due to capacitative effects,capacitanceto ground is an important factor in effectiveness of signal grounds. Because of this, a complex system of buried rods and wires can be effective. An ideal signal ground maintains a fixed potential (zero) regardless of how muchelectric currentflows into g

33、round or out of ground. Lowimpedanceat the signal frequency of the electrode-to-earth connection determines its quality, and that quality is improved by increasing the surface area of the electrode in contact with the earth, increasing the depth to which it is driven, using several connected ground

34、rods, increasing the moisture content of the soil, improving the conductive mineral content of the soil, and increasing the land area covered by the ground system.Some types of transmittingantennasystems in the VLF, LF, MF and lower SW range must have a good ground to operate efficiently. For exampl

35、e, a verticalmonopole antennarequires aground planethat often consists of an interconnected network of wires running radially away from the base of the antenna for a distance about equal to the height of the antenna. Sometimes acounterpoiseis used as a ground plane, supported above the ground.AC pow

36、er wiring installationseditSee also:Earthing systemIn amains electricity(AC power) wiring installation, the termgroundconductortypically refers to three different conductors or conductor systems as listed below.Equipment earthing conductorsprovide an electrical connection between non-current-carryin

37、g metallic parts of equipment and the earth. According to the U.S.National Electrical Code(NEC), the reason for doing this is to limit the voltage imposed by lightning, line surges, and contact with higher voltage lines. The equipment earthing conductor is usually also used as the equipment bonding

38、conductor (see below).Equipment bonding conductorsprovide a low impedance path between non-current-carrying metallic parts of equipment and one of the conductors of that electrical systems source, so that if a part becomes energized for any reason, such as a frayed or damaged conductor, a short circ

39、uit will occur and operate a circuit breaker or fuse to disconnect the faulted circuit. Note that the earth itself has no role in this fault-clearing process3since current must return to its source, not the earth as is sometimes believedcitation needed(seeKirchhoffs circuit laws). By bonding (interc

40、onnecting) all exposed non-current carrying metal objects together, they should remain near the same potential thus reducing the chance of a shock. This is especially important in bathrooms where one may be in contact with several different metallic systems such as supply and drain pipes and applian

41、ce frames. The equipment bonding conductor is usually also used as the equipment earthing conductor (see above).Agrounding electrode conductorconnects one leg of an electrical system to one or more earth electrodes. This is called system grounding and most systems are required to be grounded. The U.

42、S. NEC and the UKsBS 7671list systems that are required to be grounded. The grounding electrode conductor is connected to the leg of the electrical system that is the neutral wire. The grounding electrode conductor is also usually bonded to pipework and structural steel in larger structures. Accordi

43、ng to the NEC, the purpose of earthing an electrical system is to limit the voltage to earth imposed by lightning events and contact with higher voltage lines, and also to stabilize the voltage to earth during normal operation. In the past,water supplypipes were often used as ground electrodes, but

44、this was banned where plastic pipes are popular. This type of ground applies to radio antennas and to lightning protection systems.Permanently installed electrical equipment usually also has permanently connected grounding conductors. Portable electrical devices with metal cases may have them connec

45、ted to earth ground by a pin in the interconnecting plug (seeDomestic AC power plugs and sockets). The size of power ground conductors is usually regulated by local or national wiring regulations.Power transmissioneditInSingle Wire Earth Return(SWER) AC electrical distribution systems, costs are sav

46、ed by using just a single high voltage conductor for thepower grid, while routing the AC return current through the earth. This system is mostly used in rural areas where large earth currents will not otherwise cause hazards.Somehigh-voltage direct-current(HVDC) power transmission systems use the gr

47、ound as second conductor. This is especially common in schemes with submarine cables, as sea water is a good conductor. Buried grounding electrodes are used to make the connection to the earth. The site of these electrodes must be chosen carefully to prevent electrochemical corrosion on underground

48、structures.A particular concern in design ofelectrical substationsisearth potential rise. When very large fault currents are injected into the earth, the area around the point of injection may rise to a high potential with respect to distant points. This is due to the limited finite conductivity of the layers of soil in the earth. The gradient of the voltage (changing voltage within a distance) may be so high t