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