单项选择题
A.电枢绕组的电流; B.主极绕组的电流; C.牵引电机电压方向;
A.接地; B.过压; C.过流;
A.晶闸管不等分三段桥级间平滑调压; B.晶闸管不等分三段半控桥式平滑调压; C.晶闸管不等分三段全控桥平滑调压