问题 单项选择题

电动机采用y-△换接启动时,其y接启动电流和△接启动电流之间的关系和其y接启动转矩和△接启动转矩之间的关系是()。

A.A

B.B

C.C

D.D

答案

参考答案:C

解析:

电动机的△接启动电流IstΔ=7IN,启动电流比较大,为了减小启动电流,可采用Y-Δ换接启动,这种启动方式虽然减小了启动电流,但启动转矩也小了,所以只能用于轻载启动的控制电路中。

电动机的Y接启动电流[*],启动电流比Δ接时小,

电动机的Y接启动转矩[*],Y接启动转矩也小。

[点评] 本题考察的知识点是三相异步电动机的启动。

选择题
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阅读理解。

     Something in chocolate could be used to stop coughs and lead to more effective medicines, say UK

researchers.

     Their study found that theobromine, found in cocoa, was nearly a third more effective in stopping

coughs than codeine, which was considered the best cough medicine at present.

     The Imperial College London researchers who published their results online said the discovery could

lead to more effective cough treatment. "While coughing is not necessarily harmful (有害的) it can have

a major effect on the quality of life, and this discovery could be a huge step forward in treating this

problem," said Professor Peter Barnes.

     Ten healthy volunteers (志愿者) were given theobromine, codeine or placebo, a pill that contains no

medicine, during the experiment. Neither the volunteers nor the researchers knew who received which

pill. The researchers then measured levels of capsaicin, which is used in research to cause coughing and

as a sign of how well the medicine is stopping coughs.

     The team found that, when the volunteers were given theobromine, the capsaicin need to produce a

cough was around a third higher than in the placebo group. When they were given codeine they need only

slightly higher levers of capsaicin to cause a cough compared with the placebo.

     The researchers said that theobromine worked by keeping down a verve activity (神经活动), which

cause coughing. They also found that unlike some standard cough treatments, theobromine caused no side

effects such as sleepiness.

1. According to Professor Barnes, theobromine _____.

A. cannot be as effective as codeine

B. can be harmful to people's health

C. cannot be separated from chocolate

D. can be a more effective cure for coughs

2. What was used in the experiment to cause coughing? 

A. Theobromine.

B. Codeine.

C. Capsaicin.

D. Placebo.

3. We learn from the text that volunteers in the experiment _____.

A. were patients with bad coughs

B. were divided into the three groups

C. received standard treatments

D. suffered little side effects

4. Which of the following would be the best title for the text?

A. Codeine: A New Medicine

B. Chocolate May Cure Coughs

C. Cough Treatment: A Hard Case

B. Theobromine Can Cause Coughs