Transformer Maintenance…in the beginning…

Power Transformers by their nature require less maintenance than other equipment in an electrical system,  Unfortunately, this is often interpreted to mean that they require no maintenance and this can lead to neglect and potentially preventable failure.

By following a scheduled and systematic maintenance and inspection program, and acting on the findings, the life of a transformer can be prolonged.  By recognizing the part played by the cooling liquid, electrical accessories, mechanical components and alarm circuitry, an adequate specification of inspection and tests can be recommended.  Maintenance staffs can make a positive contribution to their Company’s profit picture. 


The time to start a transformer maintenance program is when the equipment is new, or recently repaired, prior to being energized for the first time.  At this stage in the transformers’ life, the following tests should be performed:

  • insulation resistance (megger)
  • dissipation factor
  • oil tests for dielectric strength and water content
  • turns ratio test
  • oil test for dissolved gas in oil analysis
  • control and protective circuit checks

After a month of operation, an oil sample should again be taken for dissolved gas in oil analysis.  The results of these early tests along with the test data from the new or repair transformer Plant should be filed for future reference.  From this point on, effective decisions can be made comparing subsequent test data to the earlier obtained information.

Post Commissioning Tests – performed “regularly” as defined by the User

  • monitor liquid and winding temperature
  • monitor liquid level
  • review tank pressure (if applicable)
  • check fan and cooling pump operation (if applicable)
  • check for tank and cooler leaks

Tests – performed annually

  • oil sample for standard oil tests
  • oil sample for dissolved gas in oil analysis
  • insulation resistance (megger)
  • dissipation factor
  • turns ratio
  • gauges and relays
  • tapchanger operation
  • check bushings
  • check cooling systems
  • check controls

The owner of the transformer must make the final decision as to what continuing maintenance checks to perform.  This decision will be based on the relative importance to your operation.  If the transformer is a main source of power and its’ failure means your Plant is shut down, preventative maintenance should be given a high priority. If on the other hand the unit services a small secondary load that can easily be switched from another source, maintenance will likely be given a different emphasis.

New Transformers

  • Needs analysis
  • Develop specification or review existing documentation
  • Prepare Tender documents
  • Evaluate Tender responses on technical and commercial basis
  • Supplier evaluation
  • Quality system review
  • Design review
  • Drawing review
  • Manufacturing inspection
  • Project expediting
  • Electrical test witnessing
  • Shipping inspection
  • Maintenance program recommendations


Oil filled transformers – Rectangular and Circular core form. Core and Coil design including windings and winding instructions. Mechanical Design, bracing for vacuum and seismic requirements. Repair Plant Experience.

Mature Transformers

  • Establish maintenance procedures and cycles
  • Interpretation of Field test results including:
    • standard oil tests
      • dielectric strength
      • water content
      • power factor
      • interfacial tension
  • dissolved gas in oil analysis
  • insulation resistance (megger)
  • power/dissipation factor
  • degree of polymerization analysis
  • Failure Analysis, repair versus replace recommendations, hands on inspection and review of Factory and Field test data
  • Training seminars – customized to meet needs, general transformer knowledge and maintenance