题目内容

双速三相交流鼠笼式异步电动机常用的改变转速的方法是（）。

A. 改变电压
B. 改变极对数
C. 将定子绕组由三角形连接改为星形连接

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三相异步电动机拖动恒转矩负载，当进行变极调速时，应采用的联接方式为（）。

A. Y-Y Y
B. △-Y Y
C. 顺串Y-反串Y

选择异步电动机调速方法的基本原则是，调速范围广、调速平滑性好、调速设备简单、调速中的损耗小。（）

A. 对
B. 错

Directions: Watch the video clip and complete the sentences.1. Kate: I tried to make her laugh, told her not to worry about it, and that .2. Mark: Maybe she was just being polite. It was probably because she realized you were working and .3. Kate: I just wonder if she found it difficult to talk about her feelings with me. Maybe I shouldn’t have tried to make her laugh? Perhaps she thought I wasn’t .4. Mark: I wouldn’t worry about it. .5. Janet: Yes, I’ve just got my essay back. !

平台梁的断面形式为（）

A. 矩形
B. L型
C. T型
D. 方形