问题 问答题 简答题

在哪些情况下允许适当牺牲继电保护部分选择性?

答案

参考答案:

1、接入供电变压器的终端线路,无论是一台或多台变压器并列运行(包括多处T接供电变压器或供电线路),都允许线路侧的速动段保护按躲开变压器其他侧母线故障整定。需要时,线路速动段保护可经一短时限动作。

2、对串联供电线路,如果按逐级配合的原则将过份延长电源侧保护的动作时间,则可将容量较小的某些中间变电所按T接变电所或不配合点处理,以减少配合的级数,缩短动作时间。

3、双回线内部保护的配合,可按双回线主保护(例如横联差动保护)动作,或双回线中一回线故障时两侧零序电流(或相电流速断)保护纵续动作的条件考虑;确有困难时,允许双回线中一回线故障时,两回线的延时保护段间有不配合的情况。

4、在构成环网运行的线路中,允许设置预定的一个解列点或一回解列线路。

阅读理解

阅读理解。

     I have a seven-year-old son named John. He loves chocolates. He often takes chocolates instead of meals.

Therefore, he gets very bad teeth. The dentist (牙医) told me not to let him eat chocolates any more. But his

grandfather dotes on (宠爱) him. He often buys John chocolates even though he knows that they are bad for

teeth. I know that John is his only grandson, who is everything to him. I really don't want to make him

unhappy. Therefore, I always allow John to eat the chocolate his grandfather bought him.

    Yesterday evening I kissed John good night and asked him to say his prayers before going to bed, and then

I left his bedroom. A few minutes later, I heard John shouting word by word. "Tomorrow-is-my-birthday.

May-God-bring-me-a-big-box-of-chocolates." I went to his room and saw him kneeling on the ground

shouting out his prayers. I said, "Don't shout, John. Your Dad is sleeping now! God can hear you no matter

how softly you talk to him." Pointing to the next room where his grandpa sleeps, John said secretly, "My God

is sleeping. He can't hear me unless I wake him up."

1. Why does John's grandpa often buy John chocolates? [ ]

A. He doesn't know they are bad for his teeth

B. He loves John very much

C. He shows too much fondness for his grandson

D. He wants to make John happy

2. What did the boy do before going to bed that evening? [ ]

A. He knelt on the ground and prayed for God

B. He knelt on the ground and prayed to his grandpa for chocolates

C. He knelt on the ground and prayed for his grandpa

D. He knelt on the ground and prayed to God for chocolates

3.The sentence" Who is everything for him" means            . [ ]

A. who is his only grandson

B. who is a most important person to him

C. who is dearer to him than anything else

D. who is near and dear to him

4. The boy shouted out his prayers in order to            . [ ]

A. make God hear him

B. let his father know

C. wake up his grandpa

D. do what his father told him

单项选择题