Step-down start refers to the use of starting equipment to properly reduce the voltage and add to the stator windings of the motor to start, after the motor starts running, and then make its electrical clothing back to the rated normal operation.

　　There are four common step-down start methods: stator winding connect resistance step-down start, self-recruited transformer step-down start, ya -- delta step-down start, extension delta step-down start.

　　The rated voltage is not necessary to start the motor as long as the acceleration torque >0 is guaranteed during the starting process. See the analysis below for details.

　　The purpose of motor step-down starting is to avoid high starting torque and peak starting current, and to reduce the influence of accelerating torque and impulse current during motor starting on working machinery and power supply system.

　　The starting process of the motor is a process in which the speed rises gradually. In order to ensure that the motor can fully accelerate to the rated speed, the torque value of the motor must be greater than the torque value of the load during the whole acceleration stage, otherwise the motor's speed will stop because it cannot go up. The difference between the motor torque and the load torque is called the acceleration torque. It must always be greater than zero during the entire acceleration phase.

　　The torque value of the motor is proportional to the square of the voltage applied at the end of the stator winding (M~U2), and the current value of the motor stator is proportional to the voltage at the end of the stator (I~U). Therefore, we can reduce the starting torque and starting current by lowering a certain voltage (ensuring the acceleration torque >0).

　　The following methods are used to start blood pressure reduction:

　　1. Resistance or reactance step-down start. The starting current will produce a voltage drop in the resistance or reactance connected in series in the stator circuit, reducing the voltage on the stator windings of the motor and thus reducing the starting current.

　　2. Self-coupling compensation starting. An autotransformer is used to reduce the voltage added to the stator winding of the motor to reduce the starting current.

　　3. Star - triangle start. Star connection is used for starting. Thus, the voltage and current of stator winding connected to star at starting are only 1/1.732 of that of triangular connection, while the circuit current is only 1/3 of that of the circuit current connected to triangle direct starting.

　　4. Start the extension triangle. At this time, the phase voltage of stator winding decreases, and the starting current also decreases.