A Newly Modified Forced Oil-Cooling System and Its Impact on in-Service Transformer Oil Characteristics

This paper introduces a newly modified forced oil-cooling system in which a bypass filter (BPF) has been used. The BPF was introduced in such a way that its intake oil is the hot oil from the transformer top and the outlet is connected to the input of the oil-circulating pump. This system has been used for two transformers. Periodical measurements of the physical, chemical, and electrical transformer oil characteristics by standard testing methods before BPF operation, in operation, and after stopping its operation in the transformer have been carried out. Before BPF operation, results revealed that these characteristics are continuously deteriorating with the increase in transformer oil service period. However, when BPF is in operation, this deterioration not only has been reduced but also some of the characteristics have been improved. After the operation of BPF has been stopped, some of the characteristics resumed their deterioration. However the rates by which these characteristics are deteriorating are noticeably smaller than their initial values. The deteriorated transformer oil characteristics (without installation of BPF) were predicted by polynomial regression, multiple linear regression, and general linear multiple regression models. The efficiency and feasibility of the new cooling system in preserving in-service transformer oil characteristics have been proved and justified by quantitative evaluation of the measured and theoretically predicted deteriorated (without installation of BPF) characteristics.