When there is excessive oxidation of the oil in a transformer and contaminants in the solid insulation, the service most often recommended is Hot Oil Cleaning.

Since the insulation in a transformer’s winding is cellulose (paper), it acts as a filter and absorbs the acids that are created as the oil oxidizes. That acid breaks down the insulation. The process of Hot Oil Cleaning (oil reclamation) involves drawing the contaminated oil through a mobile vacuum oil processing unit, heating it, passing it through sub-micron filtering media, and returning the oil to the transformer.

If the oil is heated to its aniline point (65-80 °C), the hot oil will function as a solvent for its own oxidation decay products. It will not only remove oil oxidation products from the oil but will also remove sludge deposits from the paper insulation.

We monitor the flow, the transformer’s level, the temperature, moisture, and the oil’s acid number during processing. After several passes, the oil is reclaimed and the harmful agents—acids, alcohols, peroxides, aldehydes, and both dissolved and suspended sludges—are removed from the transformer.

In this video, you can see the contaminated oil actually change color during the reclaiming process. If you pay attention to the sludge deposits on the solid insulation, you’ll see that it deteriorates and is eventually removed by the process.

The oil is readily cleaned, but the cleaning of the cellulose insulation takes heat, clean oil, time, and proper flow rates. The process, however, does not restore lost life of the paper insulation.

Our mobile processing units have the capacity to perform this process on our customers transformers with consistently favorable results. Services including hot oil cleaning, restoring oxidation inhibitor, and moisture reduction are highly effective at extending the reliable life of transformers. Research shows about a six-year extension in life, on average, each time service is performed.

Read more about how you can protect your equipment with Hot Oil Cleaning, or explore our knowledge vault for more information.

May 09, 2022