问题 问答题 简答题

交流电动机绕组接地故障产生的可能原因有哪些?

答案

参考答案:

交流电动机绕组接地故障产生的可能原因有:

(1)绕组受潮,使绝缘电阻下降失去绝缘作用。

(2)绕组端部碰端盖、机座。

(3)引出线绝缘损坏与壳体相碰。

(4)定、转子相擦引起绝缘灼伤。

(5)过电压使绝缘击穿。

(6)嵌线时绝缘损坏碰铁芯。

(7)电动机长期过载或长期在环境温度过高下运行,使绝缘老化、开裂和脱落。

阅读理解

For a lang time,a boy wonder why his next-desk-pal was always the first in the class ,  whereas he could only rank the 21st.

At home,he asked his mom:“Am I more stupid than other kids? How can I alwasys fall behind? I just can’t come with an answer.”Mom was aware that her son’s selfrespect had been damaged by the ranking system,but she didn’t know what to say to help.

She tended to say that intelligence differs and that yes,her son’s friend really was the smarter boy.But that would so upset her son .Thank goodness she resisted the temption (诱惑)to say it .

Her son and his friend went on to   high school that year,but despite trying as hard as he could,her son’s friend still outdid him.But she was proud of her boy for his hard work, sincerely proud,It was aroud this time that she decided to take him on a trip to the seaside,On the trip,she at last found an answer for him.

Today her son no longer care about rankings.He doesn’t have to,for he himself is now the top of the class at the national unversity he attands,After university his Teachers and peers fully expect him to have promising career.

Invited to speak to his old high school, he mentioned a valuable childhood experience. It concerned that holiday his mother had prepared for them: “Once, on a trip to the sea, my mother and I were lying on the beach. She pointed to the sea and said to me: Do you see the seabirds fighting for food out there? When a wave comes near, the little birds rise quickly. The clumsy(笨拙的)seagulls are far slower and have to struggle to get away from the wave. But these clumsy birds prove to have the biggest, strongest wings, which allow the bird to travel the furthest. When the season changes, they leave for foreign shores, leaving the little birds behind. Son, I have a feeling that you are one of those seagulls.”

小题1:The story convey the message that.________.

A.competion between students is good for society

B.only rankings show intelligence of a child

C.chilren take competion among them to heart

D.parents should build up chilren’s self-respect小题2:Form the 2nd paragraph,we can see that the mother  

A.decided to help with her son’s homework

B.saw the negative effects of the ranking system

C.knew her son was weak in his study

D.felt sorry for her son’s bad behavior小题3:We can infer from the passage that      

A.the mother was cafeful to protect her son’s self-respect

B.the mother was not strong enough to face the truth

C.the son knew intelligence didn’t mean anything

D.the son would forget his rankings soon after leaving high school小题4: Which of the following has the similar meaning with the underlined word “outdid”?

A.was equal to   B..laughed at     C did better than    D.worked harder than

单项选择题 A1型题