I. Structural differences between variable frequency motors and ordinary motors
1. Insulation class requirements
Typically, the insulation class of variable frequency motors is F or higher, with high strength in both ground insulation and coil insulation, especially considering the ability of the insulation to withstand impulse voltage.
2. High requirements for vibration and noise during operation of variable frequency motors.
Variable frequency motors must take into account overall rigidity and strive to enhance their natural frequency to avoid resonance with various force waves.
3. Variable frequency motor cooling method
Variable frequency motors typically use forced ventilation cooling, meaning the main motor and the cooling fan motor are separate.
4. Different protection measures are required.
Variable frequency motors with a capacity exceeding 169KW are prone to magnetic circuit asymmetry and shaft current. When this shaft current combines with other high-frequency current components, it increases, causing bearing damage. Therefore, insulation measures are generally used. For constant power variable frequency motors, when the speed exceeds 3000 rpm, high-temperature resistant special grease is used to compensate for the temperature rise in the bearings.
5. The cooling systems are different.
The variable frequency motor uses a forced cooling system, meaning the main motor and the cooling fan motor are independent, ensuring continuous heat dissipation.
II. Design differences between variable frequency motors and ordinary motors
1. Electromagnetic Design
For conventional motors, the design primarily considers performance aspects such as overload capacity, starting performance, power, and efficiency. However, variable frequency motors start directly when the critical slip is close to 1, so there is no need to consider overload capacity and starting performance as much. The design mainly focuses on how to improve the motor's adaptability to non-sinusoidal power supplies.
2. Structural Design
During the design process, the main considerations are the impact of non-sinusoidal power supply characteristics on the insulation structure, vibration, noise, and cooling methods of variable frequency motors.
