The wave character of commutator wear in electrical machines

The results of research into wear on low-power ac commutator motor sliding contacts are presented in this paper. This type of motor is commonly used in the suction units of vacuum cleaners. The research comprised of periodic measurements of the commutator sliding surface profile in the transverse section, and the surface profile of the commutator bars in the longitudinal section, in relation to the axis of rotation. Additionally, periodic measurements of the magnitudes of the commutator sliding surface and the brushes taking current to the rotor windings were made. All experiments were made under the same working conditions. On the basis of research results, it was found that the waviness of the commutator surface in transverse and longitudinal sections, and commutator and brush wear, changed during the time the motor was working. As could be seen, the mechanism of wear leads to the alternate rise and fall in amplitudes of commutator surface waviness in transverse section. The displacement of peaks of waviness of the commutator surface verified that commutator wear in the transverse section was of a wave character. The magnitudes of each commutator bar’s wear, in time periods between the consecutive measurements did not have the same value, but showed a global maximum and minimum. On the basis of analysis of the discrete spectrum of the waviness of the commutator sliding surface and the magnitudes of wear, it was shown that the wear wave moves slowly and with a varied speed in an opposite direction to that of the rotor rotation. This wave not only has a basic harmonic with a length equal to the commutator perimeter, but also several higher harmonics, of which amplitudes and phases change along with the process while the motor is working. Research results also show a strong interdependence between the waviness of the commutator surface and the changes in magnitudes of its wear.