Solvent cleaning of pole transformers containing PCB contaminated insulating oil

In 1989, it was discovered that the recycled insulation oil in pole transformers for electric power supply was contaminated with trace amounts of polychlorinated biphenyls (PCBs; maximum 50 mg-PCB/kg-insulation oil). In order to remove the PCBs from transformer components using n-hexane as a solvent, we investigated the relationship between progressive stages of dismantling and cleaning results. The results are summarized as follows: (1) Based on the cleaning test results, we made an estimate of the residual PCB amount on iron and copper components. By dismantling the test pole transformers into the "iron core and coil portion" and cleaning the components, we achieved a residual PCB amount that was below the limit of detection (0.05 mg-PCB/kg-material). To achieve a residual PCB amount below the limit of detection for the transformer paper component, it was necessary to cut the paper into pieces smaller than 5 mm. We were unable to achieve a residual PCB amount below the limit of detection for the wood component. (2) Compared to Japan's stipulated limited concentration standard values for PCBs, the results of the cleaning test show that cleaning iron or copper components with PCBs only on their surface with the solvent n-hexane will satisfy the limited concentration standard values when care is taken to ensure the component surfaces have adequate contact with the cleaning solvent.