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.
Commissioning
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.
