In general, the cage rotor motor will be planned according to the frequency conversion, and at the same time the inverter (Variable-frequency Drive, VFD) drag, in different load characteristics, it is necessary to select VFDs with different functions, so now we ask a question. Can VFD be used in pole-changing multi-speed motors, winding motors, explosion-proof motors, and single-phase motors? Are there any requirements, if any?
Ordinary variable frequency motor is based on the speed regulation under the condition of one pole, and the basic speed of the pole variable multi-speed motor has two or more speeds, such as 2/4, 4/6, 4/6/12 and other common pole change speed regulation schemes. If the pole change motor adopts VFD, then there are some key control contents in terms of control and pole change process.
When switching the number of poles of the motor, it should be carried out in the abort state of the motor, otherwise the overcurrent protection action of VFD will occur due to the change of current.
The power of the extremely multi-speed motor changes greatly under different poles, so the VFD should be selected according to the criterion of high power, and the capacity of the VFD should be able to meet the operation requirements under high power conditions.
As for the motor body, when dragging with VFD, the speed of the motor will change greatly due to the change of power frequency. From the perspective of ventilation and heat dissipation of the motor body, it is necessary to consider the compliance of the temperature rise of the winding at low frequency and the compliance of the mechanical strength of the rotating parts at high speed.
VFDs with explosion-proof characteristics should be integrated with the motor body for explosion-proof planning and must be verified before they can be used.
If a VFD is used to drive a wound motor, the rotor part can be short-circuited, i.e., the rotor series resistance is not used. However, it is necessary to balance the current generated by the variable frequency drive by decreasing the capacity. At the same time, compared with the cage motor, the impedance of the wound motor is smaller, and the tripping problem caused by harmonic current is simple. Regarding the setting of the acceleration time, it is longer than that of the cage motor, and it is not recommended to drag the winding motor with a VFD.
As for the common single-phase motor, the starting winding must be coordinated, not suitable for variable frequency starting, and the operation control can be completed with a special VFD.
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