问题 问答题 简答题

电磁转差离合器的原理

答案

参考答案:电磁转差离合器也称滑差电机。又称电磁滑差离合器,电磁转差离合器主要由电枢和磁极两个旋转部分组成,电枢部分与三相异步电动机相连,是主动部分。电枢部分相当于由无穷多单元导体组成的鼠笼转子,其中流过的涡流类似于鼠笼式转子导体的电流。磁极部分与负载连接,是从动部分,磁极上励磁绕组通过滑环、电刷与整流装置连接,由整流装置提供励磁电流。电枢通常可以是鼠笼式绕组,也可以是整块铸钢。电枢部分随异步电动机的转子同速旋转,若磁极部分的励磁绕组不通入励磁电流,磁极的磁场为零,电枢与磁极二者之间既无电的联系又无磁的联系,无电磁转矩产生,磁极及关联的负载是不会转动的,这时负载相当于与电机"离开"。若磁极部分的励磁绕组通入励磁电流时,磁极部分则产生磁场,由于电枢与磁极之间有相对运动,电枢鼠笼式导体要感应电动势并产生电流。电枢载流导体受磁极的磁场作用产生电磁力及电磁转矩,磁极部分的负载跟随电枢转动,相当于电机与负载“合上”。

单项选择题
阅读理解

In the fall of 1985,I was a bright­eyed girl heading off to Howard University, aiming at a legal career and dreaming of sitting on a Supreme Court bench somewhere. Twenty­one years later I am later I am still a bright­eyed dreamer and one with quite a different tale to tell.

My grandma, an amazing woman, graduated from college at the age of 65. She was the first in our family to reach that goal. But one year after I started college, she developed cancer. I made the choice to withdraw from college to care for her. It meant that school and my personal dream would have to wait.

Then I got married with another dream: building my family with a combination of adopt and biological children. In 1999, we adopted our first son. To lay eyes on him was fantastic...and very emotional. A year later came our second adopted boy. Then followed son No. 3. In 2003, I gave birth to another boy.

You can imagine how fully occupied I became, raising four boys under the age of 8!Our home was a complete zoo...a joyous zoo. Not surprising, I never did make it back to college full­time. But I never gave up on the dream either. I had only one choice: to find a way. That meant talking as few as one class each semester.

The hardest part was feeling guilty about the time I spent away from the boys. They often wanted me to stay home with them. There certainly were times I wanted to quit.But I knew I should set an example for them to follow through the rest of their lives.

In 2007, I graduated from the University of North Carolina. It took me over 21 years to get my college degree!

I am not special, just single­minded. It always struck me that when you're looking at a big challenge from the outside it looks huge, but when you're in the midst of it, it just seems normal. Everything you want won't arrive in your life on one day. It's a process. Remember;little steps add up to big dreams.

小题1:When the author went to Howard University, her dream was to be ________.

A.a writer

B.a teacher

C.a judge

D.a doctor小题2:Why did the author quit school in her second year of college?

A.She wanted to study by herself.

B.She fell in love and got married.

C.She suffered from a serious illness.

D.She decided to look after her grandma.小题3:What can we learn about the author from Paragraphs 4 and 5?

A.She was busy yet happy with her family life.

B.She ignored her guilty feeling for her sons.

C.She wanted to remain a full­time housewife.

D.She was too confused to make a correct choice.小题4:What does the author mostly want to tell us in the last paragraph?

A.Failure is the mother of success.

B.Little by little,one goes far.

C.Every coin has two sides.

D.Well begun, half done.