Page 229 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

7 Overheating of coil Over-voltage. Check and correct terminal voltage.
Short circuited turns in coils Replace coil.
caused by mechanical damage
or corrosion.
High ambient temperature. Relocate starter in a more suitable
area or use a fan.
Dirt or rust on pole faces Clean pole faces.
increasing the air gap.

II Overload relays/
release

1 Starter is tripping often. Incorrect setting of over load relay. Reset properly.
Sustained overload. Check for faults/excessive motor currents.

2 Failure to trip Wrong setting of O.L relay. Check O.L relay ratings and set a proper relay.
(causing motor burn Mechanical binding due to dirt, Clean or replace. Incorrect control wiring.
out). corrosion etc. Check the circuit and correct it.

III Fuses
1 Constant blowing Short circuit or poor insulation in Check the motor and the circuit
of fuses winding/wiring. for insulation resistance.
2 Fuse not blowing under Fuse rating too high. Replace with suitable fuse.
short circuit condition.
3 Fuse blowing off Fuse rating too low. Replace with suitable fuse.
frequently. Overloading of feeder. Check for over-current, leakage and short
circuit.

Troubleshooting in DC machines

Objectives: At the end of this lesson you shall be able to
• use the trouble shooting chart to rectify defects in i) DC machines in general ii) DC motors iii) DC generators.

DC machines have Power problems which are not normally found in AC machines. DC motors and generators
have commutators and brushes, which cause special problems. If the commutator is properly maintained, it will
give many years of useful service.
Chart 1 deals with DC motors and Chart 2 is for DC generator.

216

CITS : Power - Electrician & Wireman - Lesson 93-100