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1、精选优质文档-倾情为你奉上英文文献Cirtcuit BreakersA circuit breaker is mechanical switching device capable of making,and breaking currents under normal circuit conditions and also making.carring for a specified time ,and mediujm in which circuit interruption is performed may be designated by a suitable prefix, for
2、example,air-blastcircuit breaker,oil circuit breaker.The circuit breakers currently in use can be dlassified into the following categories according to the arc-quenching principles:air swetches oel ciryit breakers,minmum-oil circuit breakers,air-blast circuit breakers,the magenetic air circuit break
3、ers,minimum-oil circuit breakers,aer-blast circuit breakers,the by voltage,insulation levelcurrent,interrupting capabilities,transient recovery coltage,interrupting tiome,and trip delay.The nameplate on a circuit breaker usually indicates:.The maximum steady-state current it can carry, 2. The maximu
4、m interrupting current,3. The maximum line voltage,4.The interrupting time in cycles, The interrupting time in may last form 3 to 8 cycles on a 60 Hz system. To interrubt large currents quickly, we have to ensure rapid cooling. High-speed interruption lunits the damage transmission lines and equipme
5、nt and, equally important,it helps to mainmain the stability of the system whenever a contingency occurs. The main parts of a circuit breaker are usually:arc-quenching chamber (or interrupter with moving and fixed contacts) operating mechanism and supporting structures. Air Switches-With increasing
6、currents and voltages, spring-action driving mechanisms were developed to reduce contact buring by faster-opening operation.Later,main contacts were fitted with arcing contacts of special material and shape,which opend after and closed before the main contacts.Further improvements of the air switch
7、were the bursh-type contact with a wiping and cleaning function,the insulating barrier leading to arc chutes,and blowout coils with excellent arc-extinguishing properties.These features,as well as the horn gap contact,are still in use in low voltage as and de breakers. Oil Circuit Breaker Around 190
8、0, in order to cope with the new requirement for “interrupting capacity”,AC switches were immersed in a tank of oil. Is very effective in quenching the arc and establishing the open break after current zero.Deion grids,oil-blast features,pressure-tight joints and vents,new operating mechanisims,and
9、multiple interrupter were introucedover several decades to make the oil circuit breaker a reliable apparatus for system voltage up to 362Kv.Types and Construction of TransformerA transformer is a device that alternating current electric energy at one voltage level into alternating current electric e
10、nergy at another voltage level through the action of a magnetic field.It consists of two or more coils wire wrapped around a common ferromagnetic core.These coils are (usually)not directly connected. The only connection between the coils is the common magnectic flux presen within the core.One of the
11、 transformer windings is connected to a source of ac electric power,and the second(and perhaps third) transformer winding supplies electric power to loads. the transformer winding connected to the power souce is called the primary winding or input winding.and the winding connected to the loads is ca
12、lled the secondary winding or input winding.If there is a third winding on the transformer,it is called the tertiary winding.Power transformer are constructed on one of two types of cores.one type of construction consists of a simple rectangular laminated piece of steel with the transformer windings
13、 wrapped around two sides of the rectangle.This type of construction is know as coreform .The other type consists of three-legged laminated core with the windings wrapped around the center leg .This type of construction is know as shell form.In either case,the core is constructed of thin laminations
14、 electrically isolated form each other in order in order to reduce eddy currents to a minimum.The primary and secondary windings in a physical transformer are wrapped one on top of the other with the low-voltage winding innermost.Such an arrangement severs two purposes: 1.It simplifies the problem o
15、f insulating the high- voltage winding from the core.2.It results in much less leakage flux than would be the two windings were separated by a distance on the core.Power transformer are given a variety of different names, depending on their use in power systems.A transformer connected to the output
16、of a generator and used to step its voltage up to transformer levels is sometimes called unit transformer. The transformer ai the other end of the transformer line,which steps the voltage down from transmission levels to distribution levels,is called a substation transformer.Finally,the transformer
17、that takes the distribution voltage and steps is down to the final voltage ai which the power is actually used is called a distribution transformer.All these devices are essentially the same-the only difference among them is their intended use.In addition to the various power transformer, two specia
18、l-purpose transformers are used with electric machinery and power systems.The first of these special transformers is a device specially designed to sample a high voltage and produce a low secondary voltage directly proportional to it.Such a transformer is called a potential transformer.A power trans
19、former also produces a secondary voltage directly proportional to its primary voltage;the difference between a potential transformer and a power transformer is that the potential transformer is designed to handle only a very small current.The second type of special transformer is a device designed t
20、o provide a secondary current.much smaller than but directly proportional to its primary current.This device is called a current transformer.Lingting protectionThe thunder and lightning protects to connect the ground; Connect the ground to avoid the thunder the most important link of the technique,
21、ignore is a shot thunder, respond the thunder of the thunder or other form, and avoid the thunder work most all of send into the earth the thunder electric current. Store the thunder energy to behave the type to build the , current technology to still reach to not arrive, and therefore have no the r
22、easonable but good connect the ground equip to is impossible to speak about to defend the thunder.Therefore say the design, the construction is very high standard to connect the ground system is a heavy inside that defend thunders work it heavy. High electric potential that For long time, people hav
23、e an illusion, and think that connect the ground electric resistance more small avoid the thunder result and then more like, quilt object that protect safety. Certainly the electric resistance is more the small is more quick, strike by lightning to reserve time more short, the risk is more small, el
24、ectric voltage of its stride, get in touch with the the electric voltage produce the machine too the more the ?But, construction that the fulfillment proof of near and more than ten in the last yearses, with its say that connect the worth importance of ground electric resistance, not equal to say th
25、at connect the ground to equip more reasonable, importanceElectricity equipments, demand variety that nows city, there is lots of in a building inside not the congeniality connect the ground device, if avoid the thunder to connect the ground, electricity the safety to connect the ground, AC power th
26、e work to connect the ground, correspondence and calculator system to connect the ground, according to the fulfillment proof, totally use to connect the ground is an application most for extensive connect the local type. That A, the independence connect the ground: As above part for demand
27、for speak ofing connecting the ground of, all distinguish to independently establish the own to connect the ground system, and this kind of connect the local type to call the independence to connect the ground. Its advantage is each system and cant result in the mutual interference, and this is part
28、icularly important to correspondences systems.But the adoption independence that network easily were strike by lightninged is bad, so besides have to defend to explode the dangerous environment requesting to must want the adoption the independence of avoid the thunder method generally not lay claim
29、to the way to connect the ground. Two, totally use to connect the ground: Also call unify to connect the ground.The each system that it connect the ground the demand unifies to receive a connect the ground to equip top, or is originally each system of connect the ground device to pass the undergroun
30、d to perhaps and up link, make them the electricity for becoming of its to connect the ground to unify the ground net with metals conductor, like this of connect the local type is to totally use to connect the ground. it is current to use to connect the ground totally applied the most extensive conn
31、ect the local type. Each system that Three, connect the ground 1:00: Method that connecting the ground line to receive to connect the same point or same metals flat surface of line of ground mother of each system is up, like this call connect the ground 1:00 method. connect 1:00 the ground
32、method can resolve the etc. Electric potential to connect the ground line the problem, can therefore lower of each system can cancellation of top of interference fundamental for of interference degree, particularly is 50 HZ work signal to system, and connect the ground method on the engineering to g
33、et the extensive application therefore and 1:00. Four, the many point connect the ground:The ground line of connecting of each system adopt many pointses short on-line connect the local type, and call to much order to connect the ground. Five, mix with to connect the ground: Metals
34、 line that so- called admixture connect the ground to is at an each circuit board in equipments to connect, or related and a few equipmentses of signal electric circuits, with the most short line with the same of metals to link to connect the ground with the most short line and machine hull, then th
35、e equipments of many sets use respectively the same point top to receive the ground net. Six, the wreath form connect the ground to much used for the ground net, be connect the ground to round along building surroundings a shut to match the wreath. like this of connect the electric field that ground
36、 net can make the interface including distribute even, reduce the stride electric voltage to bane person, and also reduce the indoors while suffering strike by lightning, because of the ground electric potential the steps degree is big but produce the danger to counter-attack to equipments high pres
37、sure. Seven, the foundation connect the ground:Make use of the reinforcing bar in the building foundation, and press norm the request the conjunction to create of connect the ground to call the foundation to connect the ground.断路器空气压缩断路器是一种机械开关设备，能够在正常和特殊情况下开断电流（比如说短路电流）。例如空气断路器、油断路器，干扰电路的导体因该安全可靠的应
38、用于其中，电流断路器按灭弧远离通常被分为如下等级：空气开关断路器、油断路器、少油断路器、压缩空气断路器、具有消磁性质的隔离开关、六氟化硫断路器和真空断路器。他们的参数有电压等级、绝缘等级、电流开断容量、开断时间的瞬时电压恢复和条炸事件。断路器的铭牌通常包括：1.最大可承受电流；2.最大中断电流；3.最大线路电压；4.中断周期数量。在60hHZ的系统中，中断可能持续3-至8个周期，为了快速中断达负荷电流，我们不得不确保它的持续冷却，、高速开断能限制对传输线路的损害，这一点是同等重要的它帮助系统在任何事故发生时维持稳定运行，断路器主要由操作机构、执行机构和灭弧室组成。 当有触发电流或者电压时，空气
39、隔离开关的弹簧操作机构迅速动作以用来减少触点的烧损，主触点的特殊形状和使用材料完全适合电弧的接触，空气隔离开关更进一步的改进是由于灭胡贤泉的性能、绝缘隔板组成的灭弧罩、带灭弧功能的触头等这些特殊性质，所以仍被应用于低电压等级和直流断路器中。 多油断路器出现于1900前后，主要用来满足新斯的开断容量的要求，交流开关被浸入一个油缸之中，油在熄灭电弧和在电流过零时建立开断功能是十分有效，灭弧栅、喷油嘴、鸭梨锄头、新的操作机构和多种新的断路功能在近几十年引进使用多油断路器能够适应362kV。变压器的类型和结构变压器是一个通过磁场作用将一个交流电压值变成另一个电压值的设备。它由2条或更多的金属丝缠绕在一
40、个核心磁铁上组成的。这些绕线（一般）不直接接触。绕线之间唯一的联系是它们共有的存在于磁芯的磁通量。 一组变压器绕组连接到一个交流电源上，同时第二组（或许第三组）变压器绕组作为电源提供给负载。连接到电源上的变压器绕组叫做一次绕组，或者输入绕组。连接负载的绕组叫做二次绕组或者输出绕组。如果电压器上有第三绕组，它叫做三次绕组。 电力变压器由一两种磁芯中的一种构成。一种构造是由一种简单的变压器绕组缠绕在矩形两边的矩形薄钢片组成。这种构造类型被认为是核心形式。另一种类型是由绕组缠绕在中心引脚的3引脚叠片铁心构成。这种构造类型贝壳形式。其中任意一种类型，磁心都是由排列整齐的彼此之间电气隔离的薄迭片构成，以
41、便将涡流减小到最小值。 一个物理变压器的一次绕组和二次绕组被缠绕成一个在内部的另一个低压绕组的上面。这样安排达到了两个目的：1.它简化了从磁芯到高压绕组的绝缘问题。2. 与过去将两个绕组在磁心上隔离一定距离比起来，它导致更少的漏通量。 电力变压器被赋予了很多不同的名字，取决于它们在当前系统中的作用。一变压器连接到一个发电机的输出端，并且用于步调它的电压达到变压器值有时被叫做单位变压器。变压器一个排在另一个后面将电压从传送值步降到分布值，被叫做变电站。最后，变压器将分布电压和步幅降到最后的实际使用的电能被叫做发送变压器。所有这些设备本质上都是相同的它们之间唯一不同的是它们的特定用途。防雷保护雷电
42、保护接地是避雷技术最重要的环节，不管是直击雷、感应雷或其他形式的雷，避雷 工作的最终都是把雷电流送入大地。储存雷能量为人类造福，目前科技还达不到，因此没 有合理而良好的接地装置是不可能谈及防雷的。所以说设计、施工好高标准的接地系统是 防雷工作的重中之重。 长期以来，人们有一个错觉，认为接地电阻越小避雷效果就越好，被保护的对 象就安全。当然电阻越小散流越快，雷击的高电位保留时间越短，危险性越小，其跨步电 压、接触电压产生的机遇也就越小。但是，近十几年来的实践证明，与其说接地电阻值重 要，不如说接地装置的结构更合理、重要。现在的城市，在一座建筑物内有许多不同性质的电气设备，需要多
43、种接地装置 ，如避雷接地、电气安全接地、交流电源工作接地、通信及计算机系统接地，根据实践证 明，共用接地是应用最为广泛的接地方式。一、 独立接地：如上面所谈到的需要接地的部分，都分别独立地建立自己的接 地系统，这种接地方式称为独立接地。它的好处是各系统之间不会造成互相干扰，这对通 信系统尤其重要。但网络容易被雷击坏，故除有防爆炸要求的危险环境必须要采用独立的 避雷方式外，一般不主张采用独立接地的方式。二、 共用接地：也叫统一接地。它是把 需要接地的各个系统统一接到一个接地装置上，或者把各系统原来的接地装置通过地下或 者地上用金属导体连接起来，使它们之间成为畅通的电气接地统一地网，这样的接地方式
44、 为共用接地。共用接地是目前应用最广泛的接地方式。三、 一点接地：把各系统的接地线接到接地母线同一点或同一金属平面上，这 样的方法叫一点接地法。一点接地法能解决各系统接地线的等电位问题，所以能够降低 各系统之间的干扰程度，尤其是50HZ工频信号对系统的干扰基本上得以消除，所以一点接 地法在工程上得到广泛应用。 四、 多点接地：各系统的接地线采用多点短连线的接地方式，称作多点接地。 五、 混合接地：所谓混合接地是在一部设备内的各电路板以最短的导线与机壳 连接，或者信号电路相关的几部设备，以最短的导线与同一个金属体连接接地，然后多台 设备分别用金属线接到地网的同一点上。六、 环形接地多用于地网，就是把接地体沿建筑物周围围成一个闭合环。这样 的接地网可以使到界面以内的电场分布比较均匀，减少跨步电压对人的危害，也减少室内 在受雷击时，由于地面电位梯度大而产生对设备高压反击的危险。七、 基础接地体：利用建筑物基础内的钢筋，按规范要求连接制作的接地体 称为基础接地体。专心-专注-专业