In 1991, SUNTEN was designated to develop cast resin insulated dry type reactor by Mechanical Industry Department and Electronic Department. Up to now, over ten patents are achieved by SUNTEN, two types of reactor ( steel core and air core) are developed including shunt reactor, series reactor, arc-supression coil assembly, earthing transformers, initiating transformers, current limiting transformers, TCR shunt reactor, filtering reactor. The voltage class is up to 35kV, the capacity is up to 30000 kvar for steel core reactor; while for air core reactor, the voltage class is up to 66kV, the capacity is up to 32800kvar per single phase.