Fig .8 Simulation results with the transition resistance of 500Ω at the fault point f1
As can be seen from Fig.8, when a fault with the transition resistance 500Ω occurs on the point f1, the fault components of the positive current at 4 and 5 of the converter stations on both sides are both positive, and the fault components of the negative current are both negative. The current fault component waveforms collected from the corresponding poles are positively correlated, with high similarity and small waveform distance. Further, the corresponding current fault waveform distance D1 is equal to 0.3882, which is smaller than the setting value of Dset2. According to the protection criterion, the fault is judged to be an internal fault.
In order to explore whether the protection works reliably and quickly when other high resistance faults occur, simulations were carried out for 250Ω and 500Ω transition resistors in different fault location respectively. And the simulation results are shown in Table 5.
Table 5 Fault identification results of high transition resistance of internal and external fault