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, which comprises a bypass filter (BPF). The BPF has been introduced in such a way that its intake oil is the hot oil from the transformer top and to deliver it at the inlet of the oilcirculating 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, the 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) have been predicted by polynomial regression, multiple linear regression, and general linear multiple regression models. The efficiency and feasibility of the new cooling system in preserving inservice transformer oil characteristics have been proved and justified by quantitative evaluation of the measured and theoretically predicted deteriorated (without installation of BPF) characteristics.