Fully sealed oil immersed power transformers have the advantages of low loss, low noise, and high efficiency, which can achieve good energy-saving effects and reduce pollution. Compared with ordinary oil immersed transformers, fuly sealed transformers eliminate oil storage tanks, and the change in oil volume is automatically adjusted and compensated by the elasticity of the corrugated sheets in the corugated oiltank. The transformer is isolated from air to prevent and slow down oil degradation and insulation aging, enhance operational reliabiity, and operate normally without maintenance.