In the re-structural design, the main consideration is also the influence of non-sinusoidal power supply characteristics on the insulation structure, vibration and noise cooling mode of the variable frequency motor. Generally pay attention to the following problems:
1) Insulation grade, generally F grade or higher, to strengthen the insulation strength of the ground insulation and the turns, especially the ability to insulate the withstand voltage.
2) For the vibration and noise of the motor, the rigidity of the motor component and the whole should be fully considered, and the natural frequency should be increased as much as possible to avoid resonance with each force wave.
3) Cooling method: Generally, forced air cooling is adopted, that is, the main motor cooling fan is driven by an independent motor.
4) Measures to prevent shaft current. For motors with a capacity exceeding 160 kW, bearing insulation measures should be adopted. Mainly due to the asymmetry of the magnetic circuit, the shaft current is also generated. When the currents generated by other high-frequency components are combined, the shaft current will increase greatly, resulting in bearing damage, so insulation measures are generally taken.
5) For constant power variable frequency motors, when the speed exceeds 3000/min, special high temperature resistant grease should be used to compensate for the temperature rise of the bearing.