This type of tap-changer was designed by Sanmen Tenglong Electric Appliance Co.Ltd. and the related factories with the help of Shenyang Transformer Research Institute in May 1 994. This tap-changer which is made of new structure , new material and new technology has the merits of reasonable in structure , handle freely, turning flexibly, locating exactly, good hermetically performance and small value of contact resistance ,it has become the new generation product in these days and has been certified by Ministry Department of China in December 1995. There are two sorts of products for this tap-changer, it is suitable for oilimmersed three phase or single-phase power transformer with frequency 50Hz or 60Hz, highest Voltage for equipment 12kV and 40.5kV and 72.5kV, rated current 63A, 125A, 250A and 400A. It can be fixed directly on transformer tank cover or tank wall, they must be working under non-energized condition.