Motor step-down start mode
Star delta buck start. The working principle of motors generally used above 7kw is that the motor adopts star connection when starting. Reduce the starting current. When the motor is started, switch to delta connection to increase the power of the motor. Because the voltage of the motor winding is 220V in star connection and 380V in delta connection. It can have manual conversion or use time relay for automatic conversion. His advantages are low cost, simple operation and convenient maintenance. Disadvantages: When the motor is star-connected, the torque of the fixed machine is low, so it cannot be started with heavy load.

2. Auto-step-down start-up uses a multi-tap autotransformer to reduce the voltage at start-up. After the start is successful, it is separated from the autotransformer, and then the motor is directly converted to group voltage operation.

An autotransformer has a high voltage side and a low voltage side. The high end is connected to the power supply, and the low voltage end is connected to the motor. Its input and output share a coil. The step-down of the raw pressure can be realized with different taps. The input and output terminals must have a common line, and there are two or three groups of common lines, such as two groups of taps. The output voltage terminal is 65%-80%, so the current when the motor starts is only 42% of the full voltage start and 64% of the motor start current. Therefore, the starting current is small, and the starting torque is already small. After starting, when the speed reaches the rated value of the motor, the connection of the autotransformer is cut off, and our 380 power supply is directly loaded. And run at full pressure. If there is an abnormality in the motor when starting, the speed cannot be raised. Explain that it is laborious to start. We can try to connect the tap of the autotransformer to the 80% position. If the current of the motor is still too large when starting, it may be that we have shortened the time of the time relay, so we adjust the time according to the actual situation. Generally speaking, its advantages are that the output voltage can be changed, the consumption is small, and the efficiency is high. , Its disadvantages are high risk, high cost, and large and small volumes.

The soft starter is a motor control device that integrates motor soft start, soft stop, light load energy saving and various protection functions. The working principle is to use the soft starter connected in series with the power supply and the motor to control the conduction angle of the internal thyristor, so that the input voltage of the motor rises gradually from zero to the preset current until the end of the start. Then give the motor full voltage operation. This step-down start is a relatively smooth

Resistor step-down starting is generally used for three-phase asynchronous motors that start with light loads. The working principle is to connect resistors in series on the stator windings of the motor. This increases the resistance and reduces the current. This method has been gradually eliminated with the change of the times and the advancement of technology.