The S11 (S13) oil-immersed transformer is an outdoor structure with high anti-pollution level and good heat dissipation. During the normal use period, there is no need to replace the transformer oil, which is truly maintenance-free and ensures the safe operation and reliability of the power grid. The transformer is equipped with a pressure release safety protection device. When the transformer fails and the pressure is too high, it can be released reliably and safely through the pressure release valve to prevent the expansion of the accident.