Settings of protection are essential to ensure the sensitivity and selectivity needed to detect defects. Making the correct settings requires the calculation of the fault currents with as little error as possible. Fault currents are influenced by the parameters of the electrical networks, including the state of the insulation and the Petersen coil, which changes during their operation electrical networks. This paper analyzes how the insulation parameters of medium voltage power lines, the parameters of the Petersen coil used to treat the neutral of the medium voltage electrical network and the value of the resistance at the fault location influence the fault current in the case of a single-phase fault. The large number of single-phase faults that occur in medium voltage electrical networks justifies this analysis. The symmetrical components method was used to calculate the fault current. The results obtained by calculation were verified experimentally by causing a single-phase-to-ground fault in a real medium voltage network. The paper presents the situations in which the analytical calculation of the single-phase-to-ground fault current can lead to inadmissibly large errors, even over 50%, but also the situations in which the errors fall below 3%.
The photovoltaic system within the "Politehnica" of University of Timişoara, Romania has a surface of the PV cells of 16.06 m 2 and a total surface of the panels of 18.30 m 2 . In the period April 2011 -February 2012 it worked with an average efficiency of 12.66% and with an annual energy efficiency of 1267.5 kWh/kW p . The installations injects electrical energy in the public grid. The PV system is used for educational practical applications for Master degree students in Solar Energy, for realization of dissertation theses and for public dissemination of information on solar energy. An assessment of the performances of the system based on measured data is provided in this communication. The results are useful for solar energy users interested in installing PV systems in the region.
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