Several troubles may arise in a d.c. motor and a few of them are discussed below:
1. Failure to start
This may be due to
(i) ground fault (ii) open or short-circuit fault
(iii) wrong connections (iv) too low supply voltage
(v) frozen bearing or (vi) excessive load.
2. Sparking at brushes
This may be due to
(i) troubles in brushes
(ii) troubles in commutator
(iii) troubles in armature or
(iv) excessive load.
- (i) Brush troubles may arise due to insufficient contact surface, too short abrush, too little spring tension or wrong brush setting.
- (ii) Commutator troubles may be due to dirt on the commutator, high mica, rough surface or eccentricity.
- (iii) Armature troubles may be due to an open armature coil. An open armature coil will cause sparking each time the open coil passes the brush. The location of this open coil is noticeable by a burnt line between segments connecting the coil.
3. Vibrations and pounding noises
These may be due to
(i) worn bearings (ii) loose parts
(iii) rotating parts hitting stationary parts (iv) armature unbalanced
(v) misalignment of machine (vi) loose coupling etc.
4. Overheating
The overheating of motor may be due to
(i) overloads (ii) sparking at the brushes
(iii) short-circuited armature or field coils (iv) too frequent starts or reversals
(v) poor ventilation (vi) incorrect voltage.
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