TL;DR
Oil leaks are most commonly from degraded flange gaskets or radiator welds. Identify the leak source, de-energize the transformer, and replace the gasket or have the weld repaired by a qualified transformer service shop.
What you might see
- oil staining on the transformer tank or base pad
- oil level in the expansion tank falling over weeks
- visible oil seeping from a flange or valve
- environmental spill response triggered
Likely causes
Degraded gasket at a radiator, inspection plate, or drain valve flange
Weld crack in the radiator section from thermal stress or age
Loose or damaged sampling valve allowing slow seepage
Over-pressurized tank from a blocked pressure relief valve
Required tools
- Replacement flange gasket (correct dimensions)
- Torque wrench for flange bolts
- Clean dielectric mineral oil (correct specification)
- Oil containment materials for environmental compliance
- PPE for medium-voltage work (for the isolation step)
Safety first
- Transformer oil is combustible. Never use open flame or spark-producing tools near the oil or near leaking oil. Control spills immediately to prevent fire hazards.
- All isolation and grounding of the transformer must be done by authorized personnel under a switching permit before any hands-on repair.
Procedure
- 1
Walk around the transformer and identify the leak location. Use chalk or tape to mark the seeping point before cleaning the area.
Warning: Stay clear of the high-voltage compartments during the external inspection. - 2
Check the oil level in the expansion tank. If the level is below the minimum mark, the transformer may not be operated until oil is restored.
- 3
If the leak is from a drain valve or sampling cock, try tightening the valve packing nut slightly to stop the seep. Do not overtighten.
- 4
If the leak is from a flange gasket, arrange a de-energization with the utility or electrical authority. Gasket replacement requires the transformer to be isolated.[1]
- 5
After isolation and grounding, drain oil below the leak point level. Remove the flange bolts, replace the gasket with a new nitrile or cork-nitrile gasket of the correct dimensions, and re-torque the flange bolts evenly in a cross pattern.[1]
- 6
Refill oil to the correct level with new dielectric mineral oil of the correct specification. Do not mix oil types or grades.
- 7
If the leak is from a radiator weld, this requires a qualified transformer repair shop. The radiator must be removed and re-welded. Do not attempt field welding on an oil-filled transformer.
- 8
Document the leak volume for environmental compliance and the repair action taken.
Sources
ABB Distribution Transformer Operation and Maintenance Manual, ABB
ABB Pad-Mount Distribution Transformer installation and maintenance instructions, oil sampling, oil fill, and gasket replacement procedures (general)
View source
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