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.