Apakah perbezaan antara motor VFD dan motor biasa?
VFD motors can meet the required speed requirements by changing the frequency of the motor according to work needs, and can adjust the speed; Namun begitu, ordinary motors cannot be adjusted with a fixed speed, and forced variable frequency regulation can cause varying degrees of damage or even burnout to the motor.
1、 Characteristics of VFD motors
1. Electromagnetic design:
1) Minimize stator and rotor resistance as much as possible. Reducing the stator resistance can reduce the fundamental copper loss to compensate for the increase in copper loss caused by higher harmonics“
2) To suppress high-order harmonics in the current, it is necessary to increase the inductance of the motor appropriately. Namun begitu, the rotor slot leakage reactance is large, and its Skin effect is also large, and the copper consumption of high-order harmonics is also increased. Oleh itu, the magnitude of the motor leakage reactance should take into account the rationality of impedance matching throughout the entire speed range.
3) The main magnetic circuit of a VFD motor is generally designed to be in an unsaturated state. One is to consider that higher harmonics will deepen the magnetic circuit saturation, and the other is to consider increasing the output voltage of the frequency converter appropriately to increase the output torque at low frequencies.
2. Structural design
When designing the structure, the main consideration is also the impact of non sinusoidal power supply characteristics on the insulation structure, vibration, noise cooling method, and other aspects of the variable frequency motor. Generally, the following issues should be noted:
1) The insulation level is generally F level or higher, and the strength of ground insulation and wire turn insulation should be strengthened, especially considering the insulation’s ability to withstand impulse voltage.
2) For the vibration and noise issues of the motor, it is necessary to fully consider the rigidity of the motor components and the overall structure, and strive to increase its natural frequency to avoid resonance with various force waves.
3) Cooling mode: forced ventilation cooling is generally adopted, and the motor Computer fan is driven by an independent motor.
4) Measures to prevent shaft current should be taken, and bearing insulation measures should be taken for motors with a capacity exceeding 160KW. The main reason is that it is prone to magnetic circuit asymmetry and also generates shaft current. When the currents generated by other high-frequency components combine, the shaft current will greatly increase, leading to bearing damage. Oleh itu, insulation measures are generally taken.
2、 Differences between variable frequency motors and ordinary motors
1. The cooling system is different
The Computer fan in the ordinary motor is fixed on the motor rotor, while the variable frequency motor is separated. So when the frequency conversion speed of an ordinary fan is too low, the slow speed of the fan may cause a decrease in air volume, and the motor may burn out due to overheating.
2. Different insulation levels
Due to the need to withstand high-frequency magnetic fields, the insulation level of VFD motors is higher than that of ordinary motors. Variable frequency motors strengthen slot insulation: the insulation material is strengthened and the thickness of the slot insulation is increased to improve the level of high-frequency voltage resistance.
3. Different electromagnetic loads
The working point of an ordinary motor is basically at the turning point of magnetic saturation. If used as a VFD motor, it is prone to saturation and generates high excitation current. Namun begitu, the design of variable frequency motors increases the electromagnetic load, making the magnetic circuit less prone to saturation.
4. Different mechanical strength
VFD motors can adjust speed arbitrarily within their speed range without damage. Generally, most ordinary motors produced in China can only operate under AC380V/50HZ conditions. Ordinary motors can be used for frequency reduction or increase, but the range should not be too large, otherwise the motor will heat up or even burn out.
