The main component of the electric welding machine is a step-down transformer. The two ends of the secondary coil are the workpiece and the welding rod. During operation, the arc is ignited. In the high temperature of the arc, the welding rod is welded to the gap of the workpiece. Since the core of the welding transformer has its own characteristics, it has the characteristic of a sharp drop in voltage, that is, the voltage drops after the welding rod ignites; when the welding rod is stuck short-circuited, the voltage drops sharply.