| At present, the operating voltage of fully mechanized coal mining face has been heightened to 3.3kV on large quantities of coal mines, which would make the accident, such as equipments damage and personal electric shock due to leakage electric malfunction, occur more continually and calamitously. The improving of work efficiency underground necessitates the power supply system of fully mechanized coal mining face working more steadily. Consequently, it has preferable economic value and practical meaning to develop an excellent and convenient leakage protection system for 3.3kV power system of underground mine.At first, we analyzed the law of parameters change during the accident of leakage electric malfunction and personal electric shock on 3.3kV power system of underground mine in this paper. And the common leakage protective rules, including zero sequence current direction principle and additional power supply principle, were comparatively introduced. The paper focused on the principle analysis of leakage protection with DC natural selection, probed into the variational rule of the detection current when the creepage resistance, the divider resistance, the sampling resistance and the capacitance to ground changed respectively changed. Then the harmonic analysis on the expression of the detection current has been done, and each of the amplitudes of the harmonic component was confirmed, the output waveform based on MATLAB simulation was educed.According to the fact of 3.3kV power system of underground mine, the paper brought out a brand-new distributed secondary protection scheme, composed of principal feed switch and subordinate feed switch. We set the principal feed switch as master station and the subordinate feed switch as slave station. The former based on additional power supply principle is non-selective; the later based on natural directive current principle is selective. And it applies the 8 bits microcontroller and takes some anti-interference countermeasures. |
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