This paper examines the frequency response of power plant grounding system exposed to the lightning current. Large amount of current generated by the stroke flow in the grounding system of power plant and dissipate in the soil.  The electric and magnetic field generated by such high voltages and currents may cause damage of equipment and may be dangerous for the personnel in power plant.  For the every given frequency obtained using Fast Fourier Transformation (FFT) of lightning current impulse, electromagnetic field theory approach is used to solve Maxell’s equation and compute scalar potential, electric and magnetic field. Also, the influence of the point in which lightning current is diffused in the grounding system is presented. Three dimensional plots of spatial distribution of scalar potential, electric and magnetic field are presented. The time domain response of scalar potential, electric and magnetic field on one profile is also presented.

In electric power systems, grid elements are often subjected to very complex and demanding disturbances or dangerous operating conditions. Determining initial fault or cause of those states is a difficult task. When fault occurs, often it is an imperative to disconnect affected grid element from the grid. This paper contains an overview of possibilities for using fuzzy logic in an assessment of primary faults in the transmission grid. The tool for this task is SCADA system, which is based on information of currents, voltages, events of protection devices and status of circuit breakers in the grid. The function model described with the membership function and fuzzy logic systems will be presented in the paper. For input data, diagnostics system uses information of protection devices tripping, states of circuit breakers and measurements of currents and voltages before and after faults.K e y w o r d s: fuzzy logic, primary faults, transmission grid Nomenclature |∆I| -absolute value of current change sensitivity I t -current after the event

In this paper the influence of different soil models on step and touch voltages are presented. Soil resistivity is the basic characteristic of soil which affects a number of parameters (temperature, humidity, salt content). Basic methods of measuring soil resistivity presented in this paper are: Wenner method, Schlumberger method, General method, Driven rod (3-probe) method and the Dipole-Dipole method. Soil resistivity measurements are used to obtain an equivalent soil model (uniform model, two-layer horizontal model, multi-layer horizontal model, vertical model and others). The CDEGS software package is used for computing GPR (Ground Potential Rise), touch and step voltage with several different soil models. The resulting effect of soil models on the grounding resistance, GPR at the surface, touch and step voltages are shown. The 3D spatial distribution and 2D presentation of all characteristic values for safety analysis are presented and plotted.

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