Overload criterions of mineral-oil-immersed distribution transformer rated 100 kVA and less using the characteristics of top-oil temperature rising

This paper presents the general recommendations for the overload criteria of mineral-oil-immersed distribution transformers rated 100 kVA and less in Korea. For this purpose, the experiments are performed to analyze the characteristics of top-oil temperature rising for distribution transformer at KERI (Korea Electrical Research Institute) from December 2000 to May 2001. Twenty pole transformers are used for the test samples and they are supplied from KEPCO (Korea Electric Power Corporation). The experiment results are represented by the critical time of overload for each transformer capacity. Finally, the authors present the overload criteria of distribution transformers for summer and winter seasons, respectively.