The core of magnetically controlled shunt reactor(MCSR)has a network-side winding

a compensator winding and a control winding. The control winding is the core part for reactive power output control

and it has a high requirement for protection performance. Based on the structure of a MCSR excitation system that had already been put into operation

the failure characteristics of grounding faults

phase to phase faults and turn-to-turn faults in control winding are analyzed in detail. This paper puts forward a new control winding protection scheme and setting calculation. It takes the low-voltage and over-current composite protection as the protection for grounding fault to effectively eliminate the dead zone. The proposed scheme takes the fundamental frequency current phase comparison protection as the protection for phase-to-phase fault to improve the sensitivity of protection

and takes the current variation protection as the protection for turn-to-turn fault

which has high sensitivity in a slight turn to turn fault. The validity of the new protection scheme is verified by the simulation results.