Page 216 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Chart 2
Troubleshooting chart for DC Generators

Symptoms Cause Remedies

Generator fails to build up a) The direction of rotation must have a) Change the direction of rotation
voltage been reversed.
b) Brushes not resting on the b) Brushes to be set over the
commutator. commutator in correct position.
c) Residual magnetism is completely c) Run the generator as a DC
lost. motor or sometime (few seconds)
or connect the field circuit to a
battery or DC voltage to reestablish
the residual magnetism.
d) Generator speed is too low. d) Generator speed should be
restored to normal speed by
increasing the prime mover
speed.
e) Short circuit in the armature. e) Rectify the short circuit in the
armature.
f) Open circuit in the armature. f) Test and rectify the open circuit.
g) Short circuit in the field circuit. g) Test and rectify the short circuit
which may be in the coil. Faulty
coil will show much less
resistance than a good coil.

h) Open circuit in field winding. h) Check the continuity of the
circuit and rectify the defect.

Maintenance procedure for DC machines

At the end of this exercise you shall be able to
• state what is meant by preventive maintenance and its importance
• describe the recommended maintenance schedule for DC motors
• explain how to maintain the maintenance record.

Preventive maintenance: Preventive maintenance of Power machines consists of routinely scheduled periodical
inspections, tests, planned minor maintenance repairs and a system of maintaining inspection records for future
reference. Preventive maintenance is a combination of routine and planned operations.

Routine operations: Routine operations are those which follow fixed schedules to maintain Power motors at
daily, weekly or at other fixed intervals.
Planned operation: By contrast, planned operation consists of additional work which is performed at irregular
frequencies, and is determined by inspection and previous operating experience or the details of defects found in
the maintenance records.

Necessity of preventive maintenance: By carrying out an effective preventive maintenance programme on
Power machines, we can eliminate major failures of the machines, accidents, heavy repair costs and loss of
production time. Proper preventive maintenance will lead to economy of operation, less down-time, dependable
machine operation, longer machine life and lower overall cost of maintenance and repair.
Scheduling of preventive maintenance: Routine periodical inspection and tests may be scheduled to be carried
out daily, weekly, monthly, half-yearly and annually depending upon the following factors.

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CITS : Power - Electrician & Wireman - Lesson 30-37