Selective leakage protection of coal mine distribution network with additional DC source

The underground coal mine is dangerous environment with gas
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. In long term operation, the insulation resistance of cable decreases, and then leads to leakage. This can result in a threat to human and production safety. The leakage fault signal is weak, and the protection methods have no selectivity. The improvement of the protection method for additional DC source is proposed in this paper. The leakage fault model of system with additional DC source is made, and the fault characteristics are given. Through analysis of the AC and DC leakage circuits respectively using the superposition theorem, the mathematical analytic expression of the fault signals is obtained. The new leakage selection method can extract the DC component from zero-sequence current, and calculate the leakage resistance of each line directly; the leakage line can be detected easily. The simulation model of MATLAB is established to verify the different leakage faults of 660V system, the results show that this new leakage selection method is simple, accurately, effectively, and that can be implemented simply.