1、外文文献2：Circuit BreaksWithin a few years of the introduction of the fuse，the growing electrical industry started looking for an alternative method of providing protection for electric circuitsThey wanted a device that would not be destroyed by its operation，that could simply be reset to restore power,
2、 and that could also be used as a means of switching for the circuitOut of this development work came the circuit breakerwhich is an electromechanical deviceThe circuit breaker is defined as a device designed to open and close a circuit by non-automatic means and to open the circuit automatically on
3、 a predetermined over-current without injure to itself when properly applied within its rating. As with other equipment，circuit breakers are divided into those rated for 1 000 volts and less and those rated for more than 1000 voltsLow-voltage circuit breakers were also divided into two distinct cate
4、gories，molded-case and power typesHowever，in the past few years the distinction between these two types has become less clea-cut as a new type of encased breaker are universally operated in air, so it is not necessary to designate them as air circuit breakers as this understoodMedium and highvoltage
5、 breakers，on the other hand，use mediums other than air in which to open the circuit and therefore must be designated as being air, gas，and so on Apart from having different voltage and continuous current ratingsbreakers have widely different interrupting ratings，response characteristics，and methods
6、of operationThe proper application of circuit breakers requires a good knowledge of all the characteristics and options available for each typeThe simplest circuitopening device is the manually operated knife switchThis switch has the basic parts required of any circuitopening device：a fixed contact
7、, a moving，an operating handle，and a baseplate or flameHowever as anyone who has opened a knife switch under load has witnessed，there is a luminous discharge drawn between the separating contacts of the switchThis discharge is called an arc，and it consists of a stream of positive and negative ions.
8、The current flowing in a circuit cannot be instantaneously interruptedAs a result，the arc continues until the switch contacts have separated far enough to finally extinguish the arcThe arc can make the opening of the switch very unsafe and unreliable when interrupting a circuit breaker must provide
9、a safer and more reliable interrupting action. The following are the means by witch lowvoltage circuit breakers can be made to safely interrupt large fault currents with a minimum of contact damage 1Fast speed of operationThe duration and severity of an arc depends in part on the speed with witch th
10、e contacts can be separated，therefore powerful spring are used to rapidly force the contacts openThese springs are compressed (charged)during the closing operationThe breaker contacts are then mechanically held closed and are released by a separate trip mechanismAn operator can initiate the opening
11、of the breaker but has no control over the speed with which the contacts separate 2Use of arcing contactsThe arc burn can cause pitting，which eventually affects the ability of the contacts to carry the load current when closedTo offset this, two parallel sets of contacts are used for each pole of th
12、e breaker，a main current carrying set and an auxiliary or arcing setWhen the breaker is tripped open, the main contacts separate first，transferring the current flow to the arcing contactsThe arcing contacts then separate a split second late，drawing the arc between them and leaving the main contacts
13、free of any arcingThis allows the surfaces of the main current carrying contacts to be made of highconductivity metal such as silver，the surfaces of the arcing contacts are then made of a tougher alloy better able to withstand the effects of arcing 3Use of arc chutes Parallel plates enclosed in the
14、form of a chute are mounted directly above the arcing contactsAs the arcing contacts separate, the resulting are creates a strong magnetic field that forces the arc upward into the platesThe arc stream is then broken into a series of small arcs，which are quickly cooled，deionized，and extinguishedThe
15、ionized gases created by the are stream must be deionized before they are expelled from the arc chute；otherwise，secondary arcing could occur between the line side terminals of the breaker, which are still energized中文译文2：断路器在引入保险丝的这几年，电气行业开始寻找一种保护电路的替代方法。它们想要一个不会被自身操作毁坏的器件，这种器件可以简单的被重置恢复供电，并且也可以作为一种开
16、关电路的方法。伴随着这种发展，断路器应运而生了。断路器是一种机电设备。按定义为按设计非自动通、断电路，当按其额定值正确应用时，它能够在预设的一个过电流的情况下自动断开电路。像其它设备一样，断路器分为1000伏及以下和超过1000伏的几个电压等级。低压断路器也可分为两种不同的类型，模塑外壳式和框架式。然而，在过去的几年里，伴随着一种新型的断路器的普遍使用，这两种类型之间的区别已经变得不那么明显了，因此没有必要去以现有的定义去指定他们为空气断路器。另一方面，中、高压断路器，使用非空气的媒介打开电路，因此必须被指定为空气、煤气等等。除了有不同的电压和额定连续电流外，断路器具有多种不同的开断电流，响应特性和操作方法。断路器的正确应用程序需要掌握每个类型的所有特性和内容。最简单的电路开启装置是手动操作的刀闸开关，这个开关有任何电路所需的基本组成部分：一个固定机构，一个可动机构，一个操作手柄和一个基
