①Insulation grade requirements are higher
Generally, the insulation grade of multi-phase motors is F grade or higher, and the insulation strength to ground and turns is strengthened, especially the ability of insulation to withstand impulse voltage.
②The vibration and noise requirements of multi-phase motors are higher
Multiphase motors should fully consider the rigidity of motor components and the whole, and try to increase their natural frequency to avoid resonance with each force wave.
③Multi-phase motors have different cooling methods
Multiphase motors generally use forced air cooling, that is, the main motor cooling fan is driven by an independent motor.
④ Different requirements for protection measures
Bearing insulation measures should be adopted for variable frequency motors with a capacity exceeding 160KW. Mainly, it is easy to produce asymmetry of the magnetic circuit, and it will also generate shaft current. When the currents generated by other high-frequency components work together, the shaft current will increase greatly, resulting in damage to the bearing, so insulation measures are generally taken. For constant power variable frequency motor, when the speed exceeds 3000/min, special grease with high temperature resistance should be used to compensate for the temperature rise of the bearing.
⑤Different cooling systems
The multi-phase motor cooling fan is powered by an independent power supply to ensure continuous cooling capacity.
The difference between single-phase motor and multi-phase motor structure
①Electromagnetic design
For ordinary asynchronous motors, the main performance parameters considered in the design are overload capacity, starting performance, efficiency and power factors. The variable frequency motor, because the critical slip is inversely proportional to the power frequency, can be started directly when the critical slip is close to 1. Therefore, overload capacity and starting performance no longer need to be considered too much, and the key problem to be solved is how to improve the motor. Adaptability to non-sinusoidal power sources.
②Structural design
In the structural design, the influence of the non-sinusoidal power supply characteristics on the insulation structure, vibration, and noise cooling methods of the multi-phase motor should also be considered.
