单项选择题
A.大轴上安装接地炭刷 B.加强大轴绝缘 C.轴承座牢固接地 D.加强轴承座绝缘
A.15S和60S B.15S和45S C.20S和70S D.20S和60S
A.静止 B.旋转 C.交变 D.脉动