230-242kv on-load-tap-changing power transformer is made of high-quality silicon-steel sheets, and laminated by steps. It is advantageous in low loss, low noise, low voltage partial discharge and high anti short-circuit capacity. The dynamical and thermal stability of this transformer, of which the coils are winded by high-quality oxygen-free copper wire as well as used pre-compressing brackets processes and interior and exterior structure. The transformer tank used wave form shell, has very nice appearance, the core is with d shape yoke and 45 angle seaming. The core and oil box are well fixed and well protected on moving. Packed in wooden case