Fig.5 Flexible DC Grid Protection Flowchart Based on the Current
Fault Component Waveform Similarity
Simulation results verification
Based on the actual parameters of the Zhangbei four-terminal flexible DC
transmission system, the PSCAD/EMTDC simulation platform was used to
build a model and debug the relevant electrical parameters to simulate
the occurrence of various faults under different operating conditions.
The fault is assumed to occur between station B3 and station F1, and the
simulation duration is 4.5s. The fault occurs at 3.5s and lasts for
0.1s, the fault sampling frequency is 10kHz and the sampling window
length is 0.4ms.
6.1 Distinction between fault lines and non-fault lines
According to the fault characteristic analysis, when a fault occurs
between the different converter stations, the current fault component
waveform similarity between converter stations will change. If a fault
occurs at the point f1 on the DC line between B3 station and F1 station,
the positive and negative current fault components of each protection
measurement installation point are extracted, and the comprehensive
distance between the positive and negative current fault component
waveforms of the two stations are calculated as DPX and DNX. The
calculation results of the comprehensive distance are listed in Table 3.
Table 3 Waveform distance of positive and negative current
fault component when a fault occurs on the DC line at the fault Point f1
between station B3 and station F1