What is an autotransformer?

自耦变压器只有一组线圈，次级线圈是从初级线圈抽头出来的，它的电能传递，除了有电磁感应传递外，还有电的传送，这种变压器硅钢片和铜线数量比一般变压器要少，常用作调节电压。

The autotransformer has only one group of coils, and the secondary coil comes out from the tap of the primary coil. Its power transmission includes not only electromagnetic induction transmission, but also electricity transmission. The number of silicon steel sheet and copper wire of this transformer is less than that of ordinary transformer, which is often used for voltage regulation.