College of Mining, National University of Science and Technology—MISIS, Moscow, Russia:
G. M. Petrov, Professor, Candidate of Engineering Sciences, petrovgm@mail.ru

Actual operation conditions in mines impose specific requirements on power networks and electric installations. This factor, in its turn, specifies safety standards for utilization of electric energy with current protection of mine personnel. Surface infrastructures of mines use up to 1 kV power networks with solidly earthed neutral for possibility of phase-to-phase and phase-to-earth voltage. However, such power network is less safe as compared with the insulated neutral. For enhancement of electrical safety of 1kV solidly earthed power networks, the Electric Installation Code, 7^th editions as of 2002, dictates to utilize different earthing systems, e.g. TNC, TN-S, TT and TN-C-S. Electric safety conditions of such power networks have not been analyzed until recently. This article analyzes different earthing systems, namely, TN-C, TN-S and TT, utilized in 1 kV solidly earthed power network in terms of a test area at a processing plant. The scope of the analysis embraces various incidents when personnel touch breakdown equipment, and analytical relations between the contact voltage and different parameters of power network are obtained for normal and transient modes. With these relations, the author compares electric safety conditions of different earthing systems used in 1 kV solidly earthed power networks.

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