In the process of repairing the inverter, it was found that the impact of the current must have an impact on the motor, the variable-frequency drive (VFD) and the power grid due to the back electromotive force in the stator winding, the electromotive force generated by the motor in the synchronous generator state and the self-induced electromotive force in the self-circulating rotor.
1. When the VFD works under normal load, the current flowing through the power equipment in the VFD flows through the winding of the motor, and its energy and voltage are mainly consumed on the winding of the motor, and will not affect it. Once the VFD suddenly shuts off the load, the current in the power equipment will lose the circuit, and a huge d/df will occur, resulting in a sharp increase of 70% in the terminal voltage of the power equipment, which will cause the power equipment to withstand excessive current impact and damage.
2. This inrush current can also damage the VFD's freewheeling diode, filter capacitor and insulation, greatly shortening the service life of the VFD.
3. Different loads on the motor shaft have different effects.
Motors of different capacities have different effects. If the motor with blower and exhaust fan is switched to the power supply after a delay of 13s due to the low back pressure formed by the air, it will not be subjected to large current impact, and the impulse current motor can fully withstand it;
If the motor is loaded with a pump, the "water hammer" effect, coupled with the back electromotive force and high water pressure during switching, will cause the motor to have a current shock greater than 20 times the rated current and a huge torque impact, resulting in motor damage. If the motor is of the old type, because the power and power factor of the motor are low, the copper loss and iron loss are large, and most of the inrush current generated by the switch is consumed in the loss of the motor, and the motor can withstand the impulse current; If the motor is a new type, because of its high power, high power factor, low power consumption, small size, light weight, most of the impact that occurs when switching will become torque impact, which will cause great harm to the motor.
Impact on the power grid. If the switching opportunity is good, the inrush current will not have much impact on the grid; If the switching time is not selected properly, the air switch will trip; If the switching time is not selected properly, it will cause disturbances and fluctuations in the power grid, and have a negative impact on the safety and product quality of the power supply system, especially for large-capacity motors.
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Product range:
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Problem Code:
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Problem Description:
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