问题 问答题 论述题

试述煤矿井下杂散电流的危害?

答案

参考答案:

架线始电机车的牵引电网,是主要的杂散电流源。牵引电网中轨道是其回电体即电机车电流需沿轨道回到牵引变流所电源负端母线。由于轨道与大地不绝缘,在轨道接缝接触不良时,可引起部分电流通过大地(包括敷设金属管道和电缆金属外皮等)等。由于产生电化学效应,金属管道。电缆金属外皮、轨道作为阳极端要被腐蚀。据统计,若常年通过1A杂散电流,在一年中就能腐蚀9kg的钢材。对金属管道和电缆金属外皮来说,腐蚀点集中,情况更为严重。

在矿井杂散电流影响下,轨道与大地间有电位差,大地不同地点有电位差。对于采用电雷管爆破的场合,若两根放炮线两点异地接触,两点间有1~1.5V电位差就会形成电流通路,造成电雷管先期引爆,严重威胁生产和工作人员的安全。

杂散电流还会产生电火花,且有引起瓦斯煤尘爆炸的危险。

阅读理解

阅读理解。

       Most dictionaries will tell you a number of things about a language. There are three important things.

  These three things are spelling, pronunciation and meanings.

       First, a dictionary will tell you the spelling of a word. If you are not sure about the spelling of a word,

  you can try to find the correct spelling in a dictionary. Words are listed in a alphabetical order-a,b,c and

  so on. For example, on a dictionary page the word "poor" p,o,o,r - comes before "poverty" - p,o,v,e,r,t,y

   - and the word "proverty" comes before the word "power" - p,o,w,e,r. The words are always given in

  alphabetical order.

       The second thing, a dictionary will tell you pronunciation. Most dictionary give phonetic, or sound,

  alphabet. The phonetic spelling will tell you how a word is pronounced. There are a few different

  phonetic alphabets. Many dictionaries use the International Phonetic Alphabet to show pronunciation.

       The third thing, a dictionary will tell you the meanings of the words. You can look up a word and find

  out what it means. Many words have more than one meaning, and a good dictionary will tell you all of the word's meanings. For example, in English the common word "get" has over 20 different meanings.

1. In the passage, which of the following is among the three important things?

A. How to write a word well.      

B. How to use a word.

C. How to make a sentence.        

D. How to read a word correctly.

2. Of the three words "remove", " remote" and "remount", _____ in a dictionary.

A. "remount" comes first and "remove" comes last

B. "remove" first and "remote" last

C. "remote" first and "remove" last

D. "remove" first and "remount" last

3. Many words have _____.

A. several meanings              

B. few meanings

C. one thing                      

D. no meaning

4. A better dictionary can tell you _____.

A. more of the word's pronunciation

B. more of the word's meanings

C. more of the word's spelling

D. more of grammer

5. Phonetic alphabets are used to show _____.

A. spelling      

B. handwriting      

C. meanings      

D. pronunciation

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