1. Alternator shows no voltage
Causes:
- Exciter field resistance is too high or there is a loss of residual magnetism.
- Short-circuit in excitation circuit probably between leads to field or alternator slip rings.
- Insulation of windings is not proper.
- Fault in AVR card.
Remedial Actions:
- Cut out all excitor field regulator resistance, and check excitation circuit connections. Lift brushes & re-excite.
- Locate the short-circuit& repair the same.
- Check insulation with Megger instrument.
- Change the AVR card.
2. Alternator excites but not to its rated voltage
Causes:
- One or more stator coils are short circuited.
- Some stator coils are connected in the wrong sequence probably after local repair.
Remedial Actions:
Locate & have defective coils replaced.
Check stator winding for symmetry and re-connect any wrongly connected coils.
3. No Load Voltage Fluctuating
Causes:
- Adjust the voltage on AVR set point potentiometer.
- Check function thyristor.
Remedial Actions:
- Change AVR if required.
- Change the thyristor, change the AVR if required.
4. Overheating
Causes:
Overload or ventilation passages blocked.
Remedial Actions:
Reduce load if possible. Blow out ventilation passages with compressed air.
5. Overheating accompanied by reduction of torque
Causes:
Short circuit between one or more stator coils.
Remedial Actions:
Locate the short circuit fault & rectify it. If necessary have new coils fitted.
6. Motor will not start on no load, or runs at low speed
Causes:
- Break at the joint, probably the star point of rotor winding of the starter.
- Bad contact at some joint of stator windings.
Remedial Actions:
- Locate the break & repair it.
- Investigate & make good contact.
7. Overheating accompanied by torque deficiency
Causes:
- Connections of star-delta switch wrong.
- Too high rotor resistance probably due to faulty contact between rotor bars and short circuiting rings.
- Short circuit in the rotor winding converting rotor effect into low resistance squirrel cage rotor.
Remedial Actions:
- Check with diagram of connections & correct the error.
- Re-solder any visibly bad connections.
- Locate short circuit and repair, having faulty coils replaced where necessary.
