Three-phase asynchronous motor Y-△ step-down starting wiring diagram.

Y-△ reduced voltage starting is also called star-delta reduced voltage starting, or star-delta reduced voltage starting for short. This design idea is still to control the starting process according to the time principle. The difference is that the motor stator windings are connected in a star shape during starting, and each phase winding withstands a voltage equal to the phase voltage of the power supply (220V), which reduces the impact of the starting current on the power grid.

In the later stage of starting, the connection is switched to a delta connection according to the preset time. The voltage endured by each phase winding is the line voltage of the power supply (380V), and the motor enters normal operation. This line can be used for any squirrel-cage asynchronous motor whose stator winding is connected in a triangle during normal operation.

Working principle:

1. Press the start button SB2, the coil of contactor KM1 is energized, and the motor M is connected to the power supply. At the same time, the coils of time relay KT and contactor KM2 are energized.

2. The coil of contactor KM2 is energized, its normally open main contact is closed, and the stator winding of motor M runs in star connection. The normally closed auxiliary contact of KM2 is disconnected, ensuring that contactor KM3 is not powered.

3. The normally open contact of the time relay KT is delayed to close; the normally closed contact is delayed to open, cutting off the power of the KM2 coil, its main contact is disconnected and the normally closed auxiliary contact is closed.

4. The coil of contactor KM3 is energized and its main contact is closed, causing the motor M to switch from star starting to delta running.

5. Press the SB1 auxiliary circuit to cut off power and each contactor releases the motor to stop powering off

Extended information:

Volume starting is at the expense of power. This is achieved in exchange for reducing the starting current. Therefore, the size of the motor power cannot be used to determine whether to use a reduced voltage start. It also depends on what kind of load it is. Generally, when the load needs to be started and the load is light and the load is heavy, the reduced voltage start can be used. Under normal circumstances, the squirrel cage The starting current of a small motor is 5-7 times the operating current, and the voltage requirement for the power grid is generally plus or minus 10%. In order to avoid excessive impact on the grid voltage, step-down starting is required. Generally, it is required to use step-down starting when the power of the squirrel-cage motor exceeds 10% of the rated power of the transformer. Only squirrel cage motors use reduced voltage starting.

In actual use, it was found that motors that need to be started with reduced voltage are required starting from 11KW, such as fans. When starting, the current of 11KW is about 7-9 times (100A). According to the normal configuration The thermal relay cannot start at all (closing the damper does not help). The thermal relay is too large and cannot protect the motor, so it is recommended to use reduced voltage to start.

On some motors with smaller starting loads, due to the short time it takes for the motor to reach constant speed, the impact of current impact during startup is small. Therefore, for motors of about 3KW, a circuit breaker with 1.5 times the rated current is selected to directly There is no problem at all when starting up and working for a long time.

Reference material: Baidu Encyclopedia - step-down startup