From Table 3, it can be seen that when a fault occurs between the preset station B3 and F1, the waveform distances of DPX and DNX between the positive and negative current fault component of the converter stations on both sides are less than the setting value Dset1, which is equal to 1, indicating a high waveform similarity. The DPX and DNX values between other stations are higher than those of the preset station B3-F1, and the waveform similarity is low. Therefore, according to (12), it can be determined that the fault occurs between station B3 and station F1. For various fault types, simulation verification between different stations is carried out. The simulation results show that the fault waveform similarity is different when a fault is set between stations. The difference can effectively distinguish fault interval from non-fault interval.
When the fault occurs between the preset stations b3-F1, On the contrary, the VALUES of DPX and DNX between other stations are greater than Dset1, and the waveform similarity is low. Therefore, according to Equation (1.12), it can be determined that the fault occurs between B3 station and F1 station. For different fault types, simulation verifications between different stations are carried out. The simulation results show that the fault waveform similarity is different when the fault settings are located between different stations. The difference can be used to identify the fault interval from the non-fault interval. Due to space limitations, the simulation results are omitted.
6.2 Internal and external fault simulation results
The setting value should take into account the most severe fault situation.
When the current fault waveform similarity is used to identify the internal and external faults, it should be able to distinguish the internal fault with high resistance from the external metallic ground fault.
Similarly, the internal fault locations from f1 to f4 are set between the two protection installation points of the DC line and the external metallic ground fault locations from f5 to f8 are set at the exit of the converter. For different positions, transition resistance and fault type, the fault simulations are carried out as follows.
6.2.1 Metal grounding fault simulation results: By running the system model and conducting fault simulation for each fault type, the simulation results of metallic ground faults of internal and external faults can be obtained, respectively, as shown in Fig.6 and Fig.7.