Probabilistic evaluation of protection system of non-stationary electrical installations

The analysis of application of non-stationary electrical installations in electric networks to 1 000 V with dead-earthed neutral is provided in the study. It is noted that the choice of means of elec-tric protection of non-stationary electrical installa-tions is carried out taking into account the analysis of the system of power supply and possibility of use of highly effective means of protection, namely de-vices of protective shutdown. The analysis of func-tioning of protective earthing with observance of relevant requirements or to its resistance, or to touch tension in IT power supply system is given at operation of mobile electrical installation and the necessity of emergency operation. At emergence of single-phase short circuit the total current of short circuit on the earth does not reach electric protec-tion setting size from overcurrent, and in emergen-cy operation of the people, touching the electrical installation case can get a fatal electric trauma, i.e. the mobile electrical installations equipped with pro-tective grounding are electrically dangerous. The probability of electroporation of the man is defined during the work with the non-stationary electrical installation equipped with protective earthing. The analysis of efficiency of zeroing of mobile electrical installations as protective measure taking into ac-count technical characteristics of the fuses and au-tomatic switches having more perfect current and time characteristics is made. Shortcomings of the system of protective zeroing of non-stationary elec-trical installations as means of protection as the high requirement of providing normalized time not fulfilling in some cases the possibility of its use are specified. The equations for the definition of the probability of electroporation f the man with various outcomes at protection by means of zeroing are given. The probabilistic assessment of system ef-fectiveness "protective shutdown - zeroing" is giv-en at straight lines and indirect touches to current carrying parts of stationary and non-stationary elec-trical installations.