Figure 12: The diagram of DC current in the UFD and DC line in modified HVDC breaker. (: short circuit occurs; : short circuit is detected, all thyristors are turned on, and MMC are blocked; : IGBT1s in the DC line are turned off; decrease faster; : current in the UFD decays to zero; : IGBT2s in the diodes branch are all turned off; : current in the DC line decays to zero).