Verification of on-site oil reclamation process by means of polarisation/ depolarisation current analysis

This work starts with the reasons why on-site oil reclamation processing was required for two 250 MVA 3-φ banks of single-phase transformers. It reviews the results of routine diagnostics and describes the application of a new off-line diagnostic tools, polarisation/ depolarisation current (PDC) analysis in the verification of the effectiveness of the oil reclamation process. The moisture in insulating paper of each unit as assessed by the new tool is reported, in addition to various insulation properties such as oil conductivity, insulation resistance, polarisation index and recovery voltage. Finally, the comparison of PDC analysis result before and after oil reclamation indicates the degree of improvement in the insulation system and the final condition of the transformers.