问题 问答题 简答题

什么是断路器断口闪络保护?

答案

参考答案:

发电机在进行同期并列的过程中,断路器合闸之前,作用于断口上的电压不断变化,有时会造成断口闪络事故。断口闪络给断路器本身造成损坏,并且可能由此引起事故扩大,破坏系统的稳定运行。断口闪络保护动作的条件是断路器三相断开位置时有负序电流出现。保护首先动作于灭磁,失效时动作于断路器失灵保护。

阅读理解

阅读理解。

                                                        "Thank you" and "Excuse me"

    American people have the habbit of saying "Thank you". They say "Thank you" whenever others help

them or say something kind to them. People of other countries do so, too. You should say "Thank you"

when someone passes you the salt on the table, when someone walking ahead of you keeps the door open

for you, or when someone says your work is well done, or you have bought a nice thing, or your city is

beautiful.

    "Thank you" is used not only between friends, but also between parents and children, brothers and

sisters, husbands and wives.

    "Excuse me" is another short sentence they use. when you hear someone say so behind you, you know

that somebody wants to walk past without touching (触及) you.

    It's not polite to break others while they are talking. If you want to speak to one of them, say "Excuse

me" first, and then begin talking. You should also do so when you want to cough or make any unpleasant

noise before others.

    There are many occasions for "Thank you" and "Excuse me". We should learn to say them in the right

situation.

根据短文内容,判断下列句子的正(A)误(B)。

( )1. If you someone says you speak very good English, you should say "Thank you".

( )2. If you want to disturb (打扰) the people who are talking, begin with "Excuse me".

( )3. You needn't say "Excuse me" when you want to cough or make any unpleasant noise before others.

单项选择题