“Galurgiya” JSC (Perm, Russia):

Kandakov Ya. V., First Category Engineer
Khuzin R. A., Chief Specialist
Lebedev Yu. A., Head of Department

Electric supply of all potassium mines of Verkhnekamskoe potassium salt deposit is realized by lines with 6 kW voltage, using isolated neutral. Distribution of electric energy to collectors is realized by cable lines. Nowadays, the length of excavations from shafts to most removed sites of shaft fields on some mines reaches 17 km. Earthing grid (including common ground and additional grounding loops) was laid by all excavations. Common ground consists of steel wire armoring and current installing (lead) sheaths of armored cables and grounding veins of flexible cables (independently from the stress value), which are continuously electrically connected between each other and adjoined to main grounders. Local grounders in conditions of potassium mines are not placed because of high specific resistance of rocks. With considering removement of collectors from main grounders (grounder near the shaft on mine surface and tubing support of one of shafts), it is rather complex to provide the required resistance of grounder. Observance of requirements of Unite Safety Rules and complete resistance of grounder in some cases does not allow to provide the electrosecurity in the time of appearance of one-phase earth connection. In connection with this, there was offered to carry out the regulation of incomplete resistance of grounder, but maximum permissible values of contact voltage. For this purpose, there were detaily considered the basic and additional grounding contours, constructed on “Uralkaliy” JSC mines. There were created the dependences of complete resistance of steel circle to alternating current with frequency of 50 Hz. According to this, induction resistance in all range of current densities is near 56.5 % of active resistance. The similar dependences were obtained for cables, made of lead and additional grounding vein. There was considered the scheme of inclusion of person in electric circuit in the time of damage of additional grounding contour. There was defined, that the most dangerous situation appears in the time of disturbance of connection of additional grounding line with electrical installation.

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