【简答题】Listen to a conversation and choose the best answer to each question you hear. 1 A. He is not happy with his pay. B. He loses interest in his job. C. He is afraid of losing his job. D. He wants to ch...
【单选题】--- She looks very happy. She ______ have passed the exam. --- I guess so. It’s not difficult after all. A. should B. could C. must D. might
【单选题】绕线式异步电动机转子串频敏变阻器启动与串电阻分级启动相比,控制线路()。串电阻优点:减少启动电流,启动转矩保持较大范围,需重载启动的设备如桥式起重机、卷扬机等。缺点:启动设备较多,一部分能量消耗在启动电阻且启动级数较少。串频敏变阻器优点:结构较简单,成本较低,维护方便,平滑启动。缺点:电感纯在COS较低,启动转矩并不很大,适于绕线式电动机轻载启动。
【简答题】新视野U-4 U1_1_1d.wmv 1. The most difficult thing 1) is Mandarin Chinese. I did it in evening classes a few years ago and I 2) it really, really difficult. 2. Probably capoeira, which is a Brazilian danc...
【简答题】A. One Important Factor in Conversation B. It's not Difficult to Talk Well C. A Famous of the Art D. Pronunciation and Usage E. What Makes a Good Talker F. Talk with Strangers 小题1:_...
【简答题】新视野U-4 U1_1_1d.wmv 1. The most difficult thing 1) is Mandarin Chinese. I did it in evening classes a few years ago and I 2) it really, really difficult. 2. Probably capoeira, which is a Brazilian danc...
【单选题】关于绕线型异步电动机转子串频敏变阻器起动方式的特点,下列叙述错误的是( )。
A.
频敏变阻器相当于一个铁心损耗很大的三相电抗器
B.
在起动过程中,频敏变阻器的电抗值和对应于铁心涡流损耗的等效电阻值随着转子电流频率的减小而自动增加
C.
随着电动机转速的增高,频敏变阻器自动平滑地减小阻抗值,从而可以限制起动电流
D.
频敏变阻器不需经过分级切换电阻就可以使电动机平稳起动