Combined with direct current(DC)50 Hz protection action events caused by transformer inrush current occurred in China southern power grid in recent years

the waveform characteristics difference of inrush current

sympathetic inrush current and fault current are simulated and studied. Under the principle of without reducing sensitivity of the protection

an optimization and improvement strategy for DC 50 Hz protection based on waveform recognition is proposed. A DC 50 Hz protection lockout model is designed and developed in the PSCAD/EMTDC control and protection simulation model based on the optimization and improvement strategy. The proposed strategy is verified by means of simulation from the change of the alternating current system strength

no-load closing angle of converter transformer and core remanence of converter transformer. The results show that the proposed strategy can realize the blocking and unlocking of DC 50 Hz protection correctly

which solves the misoperation problem of DC 50 Hz protection caused by inrush current of the transformer without affecting the safety and stability of the DC system

and it has some reference significance to the research work and protection design.