750 kV HV reactor is one of important main equipment in long EHV lines

which have a high failure rateof defect and whose original configuration conditions change owing to the changing of grid structure and operationmode. There is an EHV line whose first end reactors had acetylene in its body to bring hidden dangers during the nor-mal operation

so we carries out electromagnetic transient studies on disengaging feasibility of. It is used EMTPE

fo-cusing on power frequency overvoltage

switch-on and single-phase reclosing operating overvoltage

secondary-arccurrents and recovery voltage

and fundamental resonance overvoltage when EHV reactors running in and out ofworking. The studies have shown that the decommissioning of original EHV shunt reactors of the study line is feasi-ble

the power frequency overvoltage and operating overvoltage meeting operational requirements but also need tochange the fast reclosing to slow reclosing.