过去，异步感应电动机的主要缺陷是难于变速。
In the past, the main disadvantage of asynchronous induction motors was the difficulty of varying their speed.
由于屏蔽电动机螺栓的制造工艺所决定，在其表面及近表面易存在缺陷。
There is defects on the surface and near surface of the bolt in canned motor pump because of manufacturing technique.
分析了煤矿井下小型隔爆电动机过载、断相保护存在的缺陷，提出了改进的保护方案。
The existing defect of overload, open phase protection of minitype flameproof motor used in coal mine was analysed and its improved protection scheme was presented.
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