The magnetically controlled shunt reactor（MCSR）is a very important reactive power compensation equipment for power grid

which has the function of smooth regulating capacity

eliminating the overvoltage of operation and submersible current.The structure of MCSR is complex

and it works in the saturation state of AC and DC mixing.Its precise mathematical model construction and internal fault analysis are more complex

and there are few references at home and abroad.This paper uses Ansoft Maxwell software to build two-dimensional finite element model of MCSR

and the external circuit editor as the excitation source of the finite element model.Through simulation line winding earth fault

line winding turn-to-turn fault

control winding earth fault

control winding turn-to-turn fault

analyzed the four kinds of fault cases

the working characteristic of MCSR.