ELECTRICAL TROUBLESHOOTING

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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.