(1)Electromagnetic factors: when the reactive power or excitation current is adjusted, the spark of the carbon brush has obvious changes, and when the exciter is commutated, the carbon brush is in poor contact with the commutator, the contact resistance is too large, and the oxide film thickness of the commutator or slip ring is uneven, causing the current distribution of the carbon brush to be unbalanced: or the sudden change of load, and the sudden short circuit leads to the abnormal voltage distribution between the commutator sheets; overload and imbalance of the unit; The selection of carbon brushes is unreasonable, the spacing of carbon brushes is unequal, the quality of carbon brushes is problematic, and so on.
(2) Mechanical factors: the center of the commutator is not correct, the rotor is unbalanced, the vibration of the unit is large, the insulation between the commutator pieces is convex or the commutator is protruding, the carbon brush contact surface is not smooth, or the surface of the commutator is rough and the contact is poor; The surface of the commutator is not clean, and the air gap under the reversing pole is not qualified; The spring pressure on the carbon brush is uneven or the size is not suitable; The carbon brush is too loose in the brush grip and jumps, or the carbon brush is too tight and gets stuck in the brush grip; Or the brush grip and the surface of the collector ring are not vertical, etc.
(3) chemical factors: the unit runs in a corrosive gas, or the unit runs in the space of lack of oxygen, the surface of the commutator and the carbon brush is destroyed by a layer of naturally formed copper oxide film, the commutation that has been formed, the approximate linear resistance of the commutation no longer exists, the commutator spark intensifies in the process of reforming the oxide film on the contact surface, and the carbon brush and the commutator are polluted.
