Misunderstanding: connect electromagnetic switches and electromagnetic contactors in the output circuit of the inverter
In actual use, some occasions require the use of contactors for inverter switching: such as when the frequency conversion is faulty, switch to the power frequency state operation, or when the one-to-two method is adopted, one motor is faulty, and the inverter turns to drag another motor. Therefore, many users will think that installing electromagnetic switches and electromagnetic contactors in the output circuit of the inverter is a standard equipment and a way to safely disconnect the power supply, but in fact, there is a greater danger in this practice.
Harm
When the inverter is still running, the contactor is disconnected first, and the load is suddenly stopped, and the inrush current will make the overcurrent maintenance action, which will have a certain impact on the main circuit of the rectifier inverter. Seriously, it can even damage the IGBT of the inverter output module. Together, when the inductive motor is loaded, the inductive magnetic field energy cannot be released quickly, and high voltages will occur, which will damage the insulation of the motor and the connecting cable.
Coping strategies
The output side of the inverter is directly connected to the motor cable, and the normal start-stop motor can be completed by triggering the inverter control terminal to achieve the role of soft start and soft stop. If the contactor must be used on the output side of the frequency conversion governor, the necessary control interlock must be made between the output of the frequency conversion governor and the action of the contactor, so as to ensure that the contactor can operate as long as there is no output of the frequency conversion governor.
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