英语翻译Unit 7 ArcText A What is Arc?Do you ever recall pulling a plug from a wall、socket and seeing what appeared to be sparks?Just as shown in Fig．1．24．What you were observing,on a very small scale,was an attempt at arc formation betwee

英语翻译Unit 7 ArcText A What is Arc?Do you ever recall pulling a plug from a wall、socket and seeing what appeared to be sparks?Just as shown in Fig．1．24．What you were observing,on a very small scale,was an attempt at arc formation betwee
英语翻译
Unit 7 Arc
Text A What is Arc?
Do you ever recall pulling a plug from a wall、socket and seeing what appeared to be sparks?Just as shown in Fig．1．24．What you were observing,on a very small scale,was an attempt at arc formation between the wall contacts and the plug contacts in your hand．For the sake of this discussion,1et’s define an arc as a discharge of electric current crossing a gap between two contacts.
Fig．1．24 Typical arc
Arcs are formed when the contacts of a circuit breaker are opened ,under a load.Arcs can be very destructive and vary greatly in size and intensity．The size of the arc depends on the amount of current present when the contacts are pulled apart．
For example,an arc that forms when normal load current is broken is insignificant compared to the arc that forms when a short circuit is broken．Because arcs cannot be prevented,electrical apparatus must be designed to control them．
The heat associated with an arc creates an ionized gas environment．The more ionization,the better the conditions are for an arc to be maintained and grow． The bigger the arc,the more heat created,which increases ionization．
Arcing is a condition that must be dealt with quickly and effectively．
The important thing to remember here is that the ability of the circuit breaker to control the arc is the key to its short circuit interrupting capability．This is a critical factor for selecting circuit breakers．
A short circuit is the most devastating over current condition．
Current Zero or Zero Point is a very important aspect to arc extinguishing.At current zero,conditions are optimal for preventing an arc from continuing.The current is said to be“Current Zero ” when the sine curve is at 0.,180.and 360.． See Fig．1．25．
Voltage is also a very important consideration because it is the pressure that keeps the current moving． Left unchecked v01tage will keep pushing the current through current zero and give new life to the arc.Vo1tage does not take kindly to being stopped in its tracks during the extinguishing of an arc．If it reignites,it can damage the whole electrical system．
Circuit breakers take this process into account by simultaneously opening the contacts and extinguishing the arc． The successful extinguishing of the arc depends on the dielectric strength of the gap between the contacts． The dielectric strength is the maximum voltage a dielectric can withstand without breaking down．A dielectric is any insulating material between two conductors．In these discussions,the circuit breaker contacts are the conductors and the insulating material can be air,gas or a vacuum．If the dielectric strength is greater than the voltage trying to re-ignite the arc,the arc extinguishing will be successful.
那位英语高手帮翻译一下 要准确的

英语翻译Unit 7 ArcText A What is Arc?Do you ever recall pulling a plug from a wall、socket and seeing what appeared to be sparks?Just as shown in Fig．1．24．What you were observing,on a very small scale,was an attempt at arc formation betwee
Text A 什么是电弧?
你从墙上、插座上拔插头的时候,曾看见过火花吗?如图1.24所示.你所看见的,就是从墙到你手上的插头之间,要形成一个小型的电弧.在我们的讨论中,把电弧定义为在两个导体之间的空隙中的放电.
图1.24典型的电弧
在有负荷的情况下,断路器打开就会产生电弧.电弧可以有很大的破坏性,它的大小和强度变化范围很大.它的大小取决于电路断开时电流的大小.
比如,正常负载时断路所形成的电弧与短路时形成的电弧相比就可以忽略不计了.因为无法阻止电弧的产生,电器设备必须要有控制电弧的设计.
电弧带来的热量使周围气体发生电离.气体离子化程度越高,越有利于电弧的持续和增强.电弧越大,产生的热量越多,电离程度越高.
对于电弧的处理必须迅速有效.
这里要记住的最重要的事情是断路器控制电弧的能力是它短路断流性能的关健.这是选择断路器最重要的因素.
通电时短路是最具破坏性的.
电流零点对熄灭电弧非常重要.零点对阻止电弧持续产生是最理想的.电流被称为0,是在正弦曲线在0度、180度和360度时.
见图1.25
电压也是要考虑的重要因素,因为它是保持电流流动的压力.剩余的电压会继续推动电流通过零点,给电弧以新的生命.在电弧熄灭的过程中,电压不会好心地自己停下来.如果它重新燃起,会毁坏整个电气系统.
断路器利用这个过程断开线路并熄灭电弧.成功熄灭电弧取决于导体间电介质绝缘强度.绝缘强度是电介质在不被击穿时能承受的最大电压.电介质是两导体之间的绝缘物质.在这里的讨论中,断路器两端与导体相连,而绝缘物质可以是空气、某种气体或真空.如果绝缘强度比要重新点燃电弧的电压大,电弧就会被成功地熄灭.（我也终于成功翻完了,哈哈）