In the power system, direct current transmission is the main means of long-distance transmission. The subsequent relay protection issues also require an outcome. The relay protection of DC transmission is different from AC relay protection, but overall, the working capacity of DC protection devices in high-voltage DC transmission systems is still measured by reliability, selectivity, speed, and sensitivity. These indicators actually depend on the software and hardware performance of the protection device, the effectiveness of the protection principle, and the rationality of the protection setting. By measuring the amplitude of the DC side current of the inverter, locking the inverter when a fault current exceeds the given value is the main means of DC overcurrent protection. For DC protection, there are often significant differences in the fault process and the amount of characteristic faults related to protection under different operating modes, fault locations, and times of AC/DC systems. Therefore, before setting calculation of DC protection, it is also necessary to first simulate a set of characteristic fault waveform under different system operation modes, fault locations, and time conditions, and then select the limit values for setting calculation. For this type of characteristic fault related to protection and its limit value, it can be called the DC protection setting reserve
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