Why do these problems always occur on motor rotors?

In the failure cases of motor products, the stator part is mostly caused by the winding. The rotor part is more likely to be mechanical. For wound rotors, this also includes winding failures.

Compared with wound rotor motors, cast aluminum rotors are much less likely to have problems, but once a problem occurs, it is a more serious problem.

First, without overspeed protection, the wound rotor is more likely to have a package drop problem, that is, the end of the rotor winding is severely radially deformed, which is very likely to interfere with the end of the stator winding, and then cause the entire motor winding to burn out and mechanically jam. Therefore, the speed of the wound rotor motor cannot be too high, and the synchronous speed is generally 1500 rpm or less.

Second, the cast aluminum rotor has local or overall heating problems. If there is no problem with the design, it is more because the cast aluminum process does not meet the design, the rotor has serious broken or thin bars, and the motor has local or even large-scale heating when running. In severe cases, the rotor surface turns blue, and in more serious cases, aluminum flow occurs.

Third, for most cast aluminum rotors, the ends are relatively stable. However, if the design is unreasonable, or there are situations such as high current density and high temperature rise, the rotor ends may also have problems similar to the winding rotor, that is, the wind blades at the ends are severely radially deformed. This problem is more common in two-pole motors, and of course it is directly related to the aluminum casting process. Another serious problem is that the aluminum is directly melted, some of which occurs in the rotor slots, and some of which occurs at the rotor end ring position. Objectively speaking, when this problem occurs, it should be analyzed from the design level, and then the aluminum casting process should be comprehensively evaluated.

Compared with the stator part, due to the special nature of the rotor in motion, it should be evaluated separately from the mechanical and electrical levels, and necessary performance verification should be carried out.