When the asynchronous motor is powered on, a rotating magnetic field will be instantly generated on the motor stator, and the rotor will not reach the rated speed immediately, but will gradually accelerate from 0. Therefore, the difference between the rotor speed and the rotating magnetic field speed is very large during startup!
What will be the impact of this large speed difference?
This leads to a very large induced current on the motor rotor winding, which is 4 to 7 times the current of the motor under rated working conditions! ! !
Therefore, if a motor is started frequently (such as drilling the spindle), if a large current often passes through the winding, the motor will be burned.
How to solve the adverse effects of large current at the moment of motor starting?
We generally use motor reduced voltage starting. In many industrial scenarios, the star-angle reduced voltage starting method is used. The Y-Δ reduced voltage starting control is generally suitable for medium and high-power large three-phase asynchronous motors with Δ-shaped connection of the motor stator winding during normal operation.
The Y-Δ type step-down starting method can reduce the power line current to 1/3 of that in the Δ type connection method during starting, thus effectively avoiding the influence of excessive current on the power supply circuit.