In the current paper, the human safety issues in different power supply systems are considered. The conditions for residual-current device utilization and protective characteristics in grounded-neutral and insulated-neutral power supply systems are reviewed. Also, the endangerment factors and accident statistics are analyzed. Based on the given data, the judgment on the safety of different power supply system is given and a novel approach in the residual-current device setting up is proposed. Finally, the topology for IT system performing from TNC system is shown.

The article is devoted to the development of a mathematical model of an insulator breakdown and the methodology for assessing the development of a breakdown. The main calculation expressions are presented in the article. The design of a real insulator (the outdoor voltage insulator of 35 kV type IOSK 3/35 UHL1) is presented as an example of the technique applicability. The datasheet of this outdoor isolator was used to verify the mathematical model and the results of numerical simulation. The results of numerical simulation and the outdoor insulator breakdown voltage are presented in the article. Numerical simulation was carried out in Comsol Multiphysics software. The obtained results can be applied in the engineering design of outdoor insulators and elements of electrical constructions.