It is not only recommended, but necessary to use sealed steel containers for the storage of transformer oil. The interior of the containers should be coated with an oil resistant coating. Before filling the container, the interior must be leaned and dried. The outside of the containers must have anticorrosive protection and each container must have its own identification number.
The transformer oil reservoir equipment consists of:
- Oil inlet and outlet valves;
- Access Hatch which serves for cleaning, inspection and repair;
- Oil pickup tubes. The first one is used for sampling from the bottom of the container. The second one is located at the lowest oil sampling point at the level of an oil outlet valve; and a
- Bottom collector with 3 to 4 mm holes to allow drying the oil with dry air or nitrogen.
In order to provide ventilation, the container is connected to the atmosphere by means of a silica gel or zeolite tube. Three days after filling the container with oil, a smaple of the oil should be taken for testing.
Transformer oil that is in long term storage, should be tested at least once every three years. The testing measures such parameters as breakdown voltage, flash point, acidity index, the presence of mechanical impurities and water and moisture.
It is also recommended to perform an analysis of the oil taken from the two oil sumps at least once a year during the storage period. Breakdown voltage and dielectric dissipation factor at a temperature of 90°C should also be measured during testing.
Before the end of the transformer oil’s guaranteed storage life, the oil analysis and testing are should be performed on a full scale. The results should meet the standards set for new unused oil.
If the testing reveals that the oil does not meet the new oil standards, it will be necessary to find out the cause of the problem. Once the problem has been identified, it should be resolvedd by the most approporaite means available. The problem must be eliminated and then the oil can be restored to its new like condition.