Ans. Besides giving trouble themselves, the heat may be conducted along the armature shaft and core, thus giving rise to excessive heating of the armature.

POINTS RELATING TO HOT BEARINGS

  1. Use good oil;
  2. See that oil cups or reservoirs are full and all oil passages clear;
  3. In self-oiling and splash systems where the oil is used over again, it should be kept in clean condition by frequent straining;
  4. Keep bearings clean and properly adjusted;
  5. Maintain bearings in good alignment;
  6. Avoid tight belts;
  7. Examine the air gap or clearance between armature and pole faces and see that they are uniform.

Ques. What troubles are encountered with short circuits in the armature or commutator?

Ans. This results in sparking at the brushes, and in the heating of one or more of the armature coils, and even in the burning up of the latter if a bad case.

When the armature is overheated, and the defect does not proceed from an overload or the causes mentioned below, the dynamo should be immediately stopped and tested for this fault.

Ques. What will happen with an overheated commutator?

Ans. It will decompose carbon brushes and cover the commutator with a black film, which offers resistance and increases the heat.

Ques. What should be done if carbon brushes become hotter than the other parts?

Ans. Use higher conductivity carbon. Reduce length of brush by adjusting holder to grip brush nearer the commutator. Reinforce brushes with copper gauze, sheet copper or wires, or use some form of combined metal and carbon brush. Increase size or number of brush if necessary, so the current does not exceed 30 amperes per square inch of contact.