THE DIFFERENCE BETWEEN A REGULAR MOTOR AND A VARIABLE FREQUENCY MOTOR

There are significant differences between ordinary motors and variable frequency motors in several aspects, mainly reflected in the following:

1.Price difference: This is obvious to everyone. Variable frequency motors are about 50% more expensive. They have a greater ability to adapt to changing frequencies, while ordinary motors can only operate at a fixed frequency. Below 35Hz or above 60Hz, ordinary motors may burn out. Variable frequency motors have greater variability and handle heavier workloads, requiring more complex designs and higher-performance materials, thus generally resulting in a higher price. Ordinary motors are relatively cheaper.

2. Cooling systems: The cooling fan of an ordinary motor is connected to the motor shaft, relying on the motor's rotation to drive the fan. Therefore, at low speeds, insufficient cooling capacity can lead to overheating and burnout. In a conventional motor, the fan and motor are coaxially connected. The faster the motor rotates, the faster the fan rotates; conversely, the slower the motor rotates, the slower the fan rotates. This is because at low frequencies and low speeds, the fan cannot provide sufficient airflow, leading to motor overheating. In a variable frequency motor, as the speed decreases, the cooling airflow decreases proportionally to the cube of the speed, resulting in insufficient heat dissipation and a rapid increase in temperature, making it difficult to achieve constant torque output. Variable frequency motors, on the other hand, are equipped with independent cooling fans and are driven by independent motors, providing a constant large airflow and effectively solving the heat dissipation problem.

3. Different insulation classes: Conventional motors typically use Class B insulation, which can withstand relatively low temperature and current surges. Variable frequency motors, however, need to operate at higher frequencies and over a wider speed range. The highest frequency a variable frequency motor can reach is around 100 Hz, or even higher. Therefore, they experience significant surges in current, requiring Class F insulation or even higher insulation materials to withstand the damage caused by high-frequency currents and voltages.

4. Frequency converters generate harmonics of different frequencies during operation. The voltage and current cause the motor to operate under non-sinusoidal voltage and current conditions. These higher-order harmonics increase stator losses, rotor losses, iron losses, and additional losses. The most significant increase is in rotor copper losses. These losses increase the motor's heat generation, reduce efficiency, and decrease output power. While the temperature rise of a conventional motor is generally higher, the carrier frequency of a frequency converter, ranging from several thousand to tens of kilohertz, forces the motor stator windings to withstand a very high rate of voltage rise, equivalent to applying a very steep surge voltage to the motor. Using ordinary materials, the temperature rise of a conventional motor is generally increased by 10% to 20%, and the inter-turn insulation of the motor faces a more severe test. Therefore, it is crucial to strengthen the motor's insulation to ground and inter-turn insulation, especially considering the insulation material's ability to withstand surge voltages.

5. Different electromagnetic load capacities, silicon steel sheets, and winding materials: Ordinary motors are prone to magnetic circuit saturation during operation, limiting their performance during variable frequency operation. Variable frequency motors, by increasing the electromagnetic load, using more silicon steel sheets, and employing higher-quality, thinner silicon steel sheets and windings, prevent magnetic circuit saturation, enabling them to provide high torque at low speeds and improving motor performance and efficiency.

6. Harmonic electromagnetic noise differs from vibration: When ordinary motors are powered by frequency converters, vibrations and noise caused by electromagnetic, mechanical, and ventilation factors become more complex. The harmonics in the frequency converter power supply interfere with the inherent harmonics of the motor's electromagnetic components, creating various electromagnetic excitation forces and increasing noise. Because motors have a wide operating frequency range and a large speed variation range, it is difficult for the frequencies of various electromagnetic force waves to avoid the inherent vibration frequencies of the motor's structural components. When the power supply frequency is low, the losses caused by higher harmonics in the power supply are greater.

7. Mechanical Structure:** Variable frequency (VFD) motors have stronger bearings, enabling them to adapt to a wider range of applications, while ordinary motors have relatively weaker bearings. VFD motors have higher requirements for vibration and noise control. The rigidity of the motor components and the overall structure must be fully considered, and the natural frequency should be maximized to avoid resonance with various magnetic waves. For motors with a capacity exceeding 160kW, VFD motors should employ bearing insulation measures. This is primarily because magnetic circuit asymmetry generates shaft current, which, when combined with current generated by high-frequency components, significantly increases the shaft current, leading to bearing damage. Therefore, insulation measures are generally required. For constant power VFD motors with speeds exceeding 3000r/min, high-temperature resistant special grease should be used to compensate for the temperature rise in the bearings.

8. Speed ​​Regulation Performance: Ordinary motors have a fixed speed, requiring external adjustment equipment to change it. The speed of ordinary motors is fixed by the grid frequency. VFD motors, on the other hand, can achieve smooth speed changes over a wider speed range, meeting the needs of different operating conditions, and possess soft-start and rapid braking functions. VFD motors support stepless speed regulation from 0 to 100%.Speed ​​Regulation Performance:Ordinary motors have a fixed speed, requiring external adjustment equipment to change the speed. The speed of ordinary motors is fixed by the grid frequency, while VFD motors can achieve smooth speed changes over a wider range, meeting the needs of different operating conditions, and have soft-start and rapid braking functions. VFD motors support stepless speed regulation from 0 to 100%.

9. Operational Stability: Ordinary motors driven by frequency converters suffer from severe ramp interference. Frequency converter motors reduce noise and voltage output differences through optimized battery design. They also use special bearings and anti-aging materials, extending their service life by 50% compared to ordinary motors.

10. Different Applications: Ordinary motors are suitable for applications requiring high speed stability, low starting current inrush, and easy maintenance, such as fans and pumps. Frequency converter motors, on the other hand, are used in applications requiring high speed control, high operating efficiency, and energy saving, such as CNC machine tools, elevators, textile machinery, and compressors.