Difference 1: Variable Frequency Motor - Variable frequency drives are used in special applications. The difference between it and a regular motor is the addition of a powerful cooling fan. The fan is powered by a separate power supply and cannot be started from the main motor. The function of the powerful cooling fan is to ensure the motor is cooled at low speeds.
Difference 2: Variable frequency motors can adjust their speed according to the load, achieving energy savings. Ordinary electric motors are fixed-speed devices that cannot be adjusted.
Difference 3: The difference is not significant, but its coil distributed capacitance is small and the silicon steel plate resistance is large, so the high-frequency pulse has little impact on the motor, and the motor's induction filtering effect is good.
Difference 4: The manufacturing processes of ordinary motors and variable frequency motors are very different. Ordinary motors, also known as power frequency motors, only need to consider the starting process and operating point at the power frequency to design the motor; variable frequency motors, on the other hand, need to consider the starting process and all points within the variable frequency range before designing the motor.
The following points are also included:
1. In terms of operating frequency, variable frequency motors are low-quality motors, while ordinary motors are good motors;
2. Because the output PWM width modulation wave of the frequency converter simulates sinusoidal alternating current, which contains a large number of harmonics, it is generally required to pass through a reactor filter before entering a conventional motor; otherwise, the conventional motor will generate heat.
3. The inverter's output PWM width modulation waveform includes a large number of harmonics. Specialized variable frequency motor. In reality, its function can be understood as a reactor and a regular motor;
4. In other words, a variable frequency motor with the same power output has a larger iron cross-section than a regular motor. The number of coil turns should be greater than the diameter of multiple conductors; high insulation, dedicated cooling fan motor;
5. Consider load-bearing capacity and high-speed rotor dynamic balance to meet the requirements of weak magnetic field speed regulation;
6. This type of variable frequency motor does not have better torque characteristics, but it overcomes the misalignment of ordinary motors with PWM analog sinusoidal AC power, which requires wide-wavelength regulation;
7. If the variable frequency motor does not meet the above characteristics and requirements, it is a fake variable frequency motor.
Compared to ordinary motors, electric motors have a constant frequency and constant voltage, and their structural differences are as follows:
1. Insulation class: Generally F or higher, the insulation strength to ground and the insulation strength of the coils should be strengthened, especially the insulation's ability to withstand impulse voltage.
2. Regarding motor vibration and noise: Fully consider the rigidity of motor components and overall rigidity, and try to increase its natural frequency to avoid resonance with various force waves.
3. Cooling method: Generally, forced ventilation cooling is adopted, that is, the main motor cooling fan is driven by an independent motor.
4. Measures to prevent axial current: Motors with a capacity greater than 160 kW should have bearing insulation measures. The main reason is that magnetic circuit asymmetry can also generate axial current. When the current generated by other high-frequency components combines with it, the axial current will increase greatly, leading to bearing damage. Therefore, insulation measures should generally be taken.
5. For constant power variable frequency motors: when the speed exceeds 3000/3min, special high-temperature resistant grease should be used to compensate for the temperature rise of the bearings.
What are the disadvantages of a conventional electric motor that operates at low frequencies for extended periods?
1. Resonance at a certain frequency;
2. This is a heat dissipation issue. When the power supply frequency is low, the losses caused by the higher harmonics in the power supply are greater. Furthermore, at low frequencies, its own fan is insufficient to cool itself, drastically reducing the motor's lifespan.
Additional information: Furthermore, the motor speed can be adjusted using a hydraulic coupling. A hydraulic coupling is a mechanical device that uses a liquid medium to transmit speed. The drive input shaft is connected to the prime mover, and the power output shaft is connected to the load shaft. The speed of the output shaft can be changed by adjusting the pressure of the liquid medium. Ideally, when the pressure approaches infinity, the output speed equals the input speed, which is equivalent to a steel coupling. When the pressure decreases, the output speed decreases accordingly. As the medium pressure continuously changes, the output speed can be adjusted indefinitely down to below the input speed.
However, hydraulic mixers are inferior to variable frequency motors in terms of speed range, speed accuracy, and efficiency, but they are relatively cheaper.
3. Ordinary motors are not allowed to operate at low frequencies for extended periods, otherwise they may burn out due to excessive heat.
