1. Alternator shows no voltage
- 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.
- 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
- One or more stator coils are short circuited.
- Some stator coils are connected in the wrong sequence probably after local repair.
Locate & have defective coils replaced.
Check stator winding for symmetry and re-connect any wrongly connected coils.
3. No Load Voltage Fluctuating
- Adjust the voltage on AVR set point potentiometer.
- Check function thyristor.
- Change AVR if required.
- Change the thyristor, change the AVR if required.
Overload or ventilation passages blocked.
Reduce load if possible. Blow out ventilation passages with compressed air.
5. Overheating accompanied by reduction of torque
Short circuit between one or more stator coils.
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
- Break at the joint, probably the star point of rotor winding of the starter.
- Bad contact at some joint of stator windings.
- Locate the break & repair it.
- Investigate & make good contact.
7. Overheating accompanied by torque deficiency
- 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.
- 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.