问题 问答题 论述题

试述如何判断电动机是定子电路单相还是转子电路单相?

答案

参考答案:

(1)根据电动机转矩来判断:定子单相时,电动机不能起动,转子只会来回摆动,发出嗡嗡响声,空载或轻载时,用手盘之能起动,电动机发热;转子单相时,电动机转矩降低,只能达到原来的10~20%,使转速显著下降,无负载或负载不超过转矩的20%时能起动。

(2)根据电动机定子电流来判断:定子电路单相时,定子电路一相电流为零(Y型接法,这是工厂起重机的通常接法)转子电路单相时,定子电路不会出现一相电流为零的情况。

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Keep safe in storms

In the spring and summer months, thunderstorms(雷雨) are common. _____小题1:____. In thunderstorms, lighting can strike(击中) people and buildings and is very dangerous.

It was reported that a man was struck by lighting when he was making a phone call under a tree. He died at once. You may not know it, but nearly 1,800 thunderstorms are happening at any moment around the world.______ 小题2:____.

So what should you do during a lighting storm? Scientists say that a person’s chances of being struck by lighting are 1 in 600,000. ____小题3:____

If you are indoors during a thunderstorm:

Stay away from anything that is metal because lighting can come into the house through it.

Don’t stand near the windows.

Don’t take a shower or bath. Lighting can travel through water.

Never use the phone.____ 小题4:______.

If you are caught in a thunderstorm outdoors:

_____小题5:_____. If there’s no building around, try to find a low place to stay in.

Do not go under a tree because the lighting could hit the tree and travel through the tree to hit you.

Never use a cell phone.

A.But you can reduce those chances by following these safety rules.

B.But it is very important for us to learn about lighting.

C.Lighting could travel through the phone line and hit you

D.In fact, many people are killed by lighting every year.E. Try to get home as soon as possible.

F. Since they happen often, some people don’t take them seriously.

G. Go into a nearby building or car right away.

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