The star-delta start, which is a buck start, is achieved by sacrificing power at the expense of reducing the startup current. Therefore, it is impossible to determine whether or not to use the star-delta start-up according to the magnitude of the motor power. Also, what kind of load is used, generally when the load is lightly running when the load needs to be started, the load can be restarted by the star-delta, and the squirrel cage is generally used. The starting current of the motor is 5-7 times of the running current, and the voltage requirement for the grid is generally plus or minus 10% (I remember) in order not to form an impact on the grid voltage too much, it is necessary to adopt the star-delta start, general requirements The star-delta start is used when the power of the squirrel cage motor exceeds 10% of the rated power of the transformer. Only the squirrel cage motor is activated with a star triangle. 1. When the load does not have strict requirements on the starting torque of the motor and the motor starting current is limited, the motor meets the 380V/Δ wiring condition, and the stator winding is connected to a triangle when the motor is in normal operation, the star-delta starting method can be adopted; 2. The method is: when the motor starts, the motor is connected to the star type wiring. When the motor starts successfully, the motor is changed into a triangle type wiring (switching quickly through the double-throw switch); 3. Since the motor starting current is proportional to the power supply voltage, and the starting current provided by the grid is only 1/3 of the full voltage starting current, the starting torque is only 1/3 of the full voltage starting torque; 4. The star-delta start is a buck start, which is achieved by reducing the start-up current at the expense of power, so it is not possible to generalize the magnitude of the motor power to determine whether or not to use the star-delta start, but also what kind of load . Generally, when the load is light at startup and the load is heavy during operation, the star-delta start can be used. Generally, the starting current of the squirrel cage motor is 5-7 times of the running current, and the voltage requirement of the power grid is generally plus or minus 10%. The motor starting current does not have an excessive impact on the grid voltage, and can be started by the star triangle. Generally, when the power of the squirrel-cage type motor exceeds 10% of the rated power of the transformer, the star-delta start is used. 5. In actual use, sometimes the motor power is 11KW, the star-delta start is required, such as a fan with a rated power of 11KW. The current is 7-9 times (100A or so) at startup, and the thermal relay can not be started normally according to the normal configuration (the damper is also useless). The thermal relay is too large to protect the motor, so it is recommended to start with the star triangle. . Stars connect U1, V1, W1; short U2, V2, W2. The triangles, U1-W2, V1U2, and W1V2 are shorted, respectively, and the power is applied to the formed triangular joint. The following figure is the main circuit diagram of the star triangle startup circuit diagram Main circuit diagram of the triangle start circuit diagram The following figure is the secondary loop control diagram of the star triangle startup circuit diagram Press SB2 - KM1 pull-in - KM1 is normally open and closed, KM1 is self-retaining, ——KM2 pull-in starts star start, time relay KT has electric delay——delay to KT normally closed to make KM2 power off release, star start stop--current is normally opened by KT, KM2 normally closed makes KM3 pull-in The coil KM3 is normally open to make the KM3 self-holding and start the angular operation - the KM3 normally closes the KT power supply. Press SB1 to stop the motor running. The time set by the "Note" time relay should be set according to the situation, which is generally determined by the time between when the motor is running and when the current drops to the rated current after starting. Star triangle secondary loop control circuit diagram 1. The motor cannot be started. Check if the voltage is off the bottom. Check if the motor is burnt out. Check if the start button and stop button are good. Whether the normally closed contact of the thermal relay is disconnected and the fuse is burnt out. 2. The motor start cannot be switched to the triangle start, and the time breaker is checked for damage. 3. When the motor starts, the current of one phase in the three phases is too high. Check whether the contacts of the contactor in the power distribution cabinet are in good contact and the bolts are tight. Star triangle electric control cabinet wiring physical map The instantaneous current of the high-power motor is 3 to 4 times of the rated current of the motor. The star-delta start can effectively reduce the starting current of the motor, prolong the service life of the motor, reduce the fluctuation of the power grid, and ensure the voltage. Quality and personal safety.
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