Auto-coupling step-down starting circuit that can avoid main contact welding accidents

In the circuit shown in the figure, the auxiliary moving and closing contacts of KM1 and KM2 and the delayed moving and breaking contacts of KT are connected in series to form an "AND" logic circuit. When the set start time expires, KT delays the moving contact action, cuts off the KM1 and KM2 coil circuits, and resets the KM1 and KM2 auxiliary moving and closing contacts. At this time, if the main contacts of KM1 or KM2 are welded, the current through the autotransformer coil can be cut off through the disconnected contacts of KM1 or KM2, thus avoiding serious heating or overheating of TA due to contact welding. Damage accidents occur. The control power supply is drawn from the QF incoming end of the main circuit breaker. By disconnecting the circuit breaker, the control circuit can be debugged without load, and the main contact pressure, stroke, etc. can be adjusted, making maintenance convenient and safe.