This series excitation transformer is the device that provides three-phase AC excitation power for the synchronous generator excitation system. The epoxy cast dry-type excitation transformer not only has the characteristics of high insulation strength, small partial discharge, strong short-circuit resistance, outstanding flame retardant performance, low operating loss, low noise, maintenance-free, and easy installation and commissioning of ordinary dry-type transformers, also has higher energy saving and higher operating efficiency.