The routine service inspection should include the following tests. Unless specific problems have been noted then the appropriate installation tests may also need to be included:
- Inspect the control cabinet, indicators, control relays, contactors, and operating mechanism.
- Check oil level in the tanks, bushings, and tap-changer compartments.
- Check for loose terminals, oil leaks, and contaminated or damaged bushings.
- Inspect the inert gas system for leakage and proper pressure.
- Check, read, and record the operation-counter indicator reading associated with the load tap changer.
- Check the oil temperature, which should not exceed the sum of maximum winding temperature (as stated on the nameplate) plus the ambient temperature (not to exceed 40°C) plus 10°C. Oil temperature does not exceed 95°C and 105°C for 55°C and 65°C winding-temperature-rise units, respectively.
Internal Inspection of Transformer
Open-type transformers that have not been inspected for at least three years should, if time permits, be given an internal inspection consisting of the following:
- Check for evidence of corrosion of tank walls and other metal parts.
- Verify connections for secureness.
- Lower the oil level to expose the top of the core coil assembly.