Analysis of factors limiting the efficiency of human protection against electric shocks in the power supply network of the mine site

Abstract

The relevance of enhancing the protection of mine personnel from electric shocks is associated with a high probability of human contact with a live phase conductor during the operation of power electrical equipment in presence of complex electrical equipment being part of the mine site. The authors have identified the following factors that limit the efficiency of the earth leakage protection means in relation to the their possible operation as part of the mine electric network used to supply power to high-capacity equipment: 1 – capacitance currents in the shunt conductances and leakage circuit are not fully compensated by autocompensators based on the correction of the compensating choke inductance; 2 – implementation of the method to detect the phase with the earth leakage by comparing the phase-to-ground voltages has a limitation for the insulation capacitances exceeding 0.9 μF/phase and the leakage resistance (human body) exceeding 1.0 kOhms; 3 – stability of the earth leakage protection devices to switching transient processes in the power line is not ensured when switching connections with high insulation capacitance in conditions of low (but still within the permissible level) active insulation resistance of the power line; 4 – functionality of the earth leakage protection is limited to cutting the energy flow of the transformer substation of the mine site off the power line and does not cover the suppression of inverse electromotive forces of the induction motors of consumers switching to the run-out mode, which represent an electrical shock hazard.