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Maintenance Process

Transformer is the heart of any power system. Hence preventive maintenance is always cost effective and time saving. Any failure to the transformer can extremely affect the whole functioning of the organization.

Maintenance Procedure

  • Transformer Oil :
    1. Oil level checking. Leakages to be attended.
    2. Oil BDV & acidity checking at regular intervals. If acidity is between 0.5 to 1mg KOH, oil should be kept under observation.
    3. BDV, Color and smell of oil are indicative.
    4. Sludge, dust, dirt ,moisture can be removed by filtration.
    5. Oil when topped up shall be of the same make. It may lead to sludge formation and acidic contents.
  • Insulation resistance of the transformer should be checked once in 6 months.
  • Megger values along with oil values indicate the condition of transformer.
  • Periodic Dissolved Gas Analysis can be carried out.


  • Bushing :
    1. Bushings should be cleaned and inspected for any cracks.
    2. Dust & dirt deposition, Salt or chemical deposition, cement or acid fumes depositions should be carefully noted and rectified.
  • Periodic checking of any loose connections of the terminations of HV & LV side.
  • Breather examination. Dehydration of Silica gel if necessary.
  • Explosion vent diaphragm examination.
  • Conservator to be cleaned from inside after every three years.
  • Regular inspection of OIL & WINDING TEMPERATURE METER readings.
  • Cleanliness in the Substation yard with all nets, vines, shrubs removed.

Protection of Transformers

  • The best way of protecting a transformer is to have good preventive maintenance schedule.
  • Oil Temperature Indicators.
  • Winding Temperature indicators.
  • Buchholz Relay.
  • Magnetic Oil level Gauge.
  • Explosion Vent.
  • HT fuse & D.O. fuse.
  • LT circuit breaker.
  • HT Circuit breaker with Over load, Earth Fault relay tripping.
  • Oil Surge Relay for OLTC.
  • PRV for OLTC.
  • HORN GAPS & Lightening Arrestor.
  • Breather.

Failures and Causes

  • Insufficient Oil level.
  • Seepage of water in oil.
  • Prolonged Over loading.
  • Single Phase loading.
  • Unbalanced loading.
  • Faulty Termination (Improper sized lugs etc).
  • Power Theft.
  • Prolonged Short Circuit.
  • Faulty operation of tap changer switch.
  • Lack of installation checks.
  • Faulty design
  • Poor Workmanship :
    1. Improper formation of core.
    2. Improper core bolt insulation.
    3. Burr to the lamination blades
    4. Improper brazing of joints.
    5. Burr /sharp edges to the winding conductor.
    6. Incomplete drying.
    7. Bad insulation covering.
    8. Insufficient cooling ducts in the winding.
  • Bad Quality of raw material.
  • Transit damaged transformers.
  • After failure, transformer is removed and replaced with new/repaired one without removing the cause of failure which results in immediate or short time failure.