FREQUENCY ANALYSIS OF THE TYPICAL IMPULSE VOLTAGE AND CURRENT WAVESHAPES OF TEST GENERATORS

Frequency analysis of the impulse waveshapes of generators which are commonly used for testing of the equipment in high-voltage engineering is presented in this paper. Some of the typical impulse waveshapes, such as 1.2/50 µs/µs, 10/350 µs/µs, 10/700 µs/µs, 10/1000 µs/µs, and 250/2500 µs/µs, are approximated by the Double-exponential function (DEXP) and by the terms of Multi-peaked analytically extended function (MP-AEF). Experimental set ups for impulse signal generation are based on the desired outputs as given in the IEC 60060-1 Standard. Dumped oscillations are characteristic of the standardized 8/20 µs/µs waveshape. The positive part of the normalized Sinc function with dumped oscillations is also approximated by MP-AEF terms. The corresponding frequency spectra of these aperiodic signals are obtained analytically by using Piecewise Fourier transform (PWFT). This paper presents the procedure to obtain Fourier transforms of the functions with multiple and sharp peaks typical for the impulse current and voltage test generators’ waveshape

Frequency domain analysis of lightning protection using four lightning protection rods

In this paper the lightning discharge channel is modeled as a vertical monopole antenna excited by a pulse generator at its base. The lightning electromagnetic field of a nearby lightning discharge in the case of lightning protection using four vertical lightning protection rods was determined in the frequency domain. Unknown current distributions were determined by numerical solving of a system of integral equations of two potentials using the Point Matching Method and polynomial approximation of the current distributions. The influence of the real ground, treated as homogeneous loss half-space of known electrical parameters, expressed through a Sommerfeld integral kernel, was modeled using a new Two-image approximation which gives good results in both near and far fields

NEW FUNCTION FOR REPRESENTING IEC 61000-4-2 STANDARD ELECTROSTATIC DISCHARGE CURRENT

New function for representing electrostatic discharge (ESD) currents according to the IEC 61000-4-2 Standard current is proposed in this paper. Good agreement with the Standard defined parameters is obtained. This function is compared to other functions from literature. Its first derivative needed for field calculations is analyzed in the paper. Main advantages are simplified choice of parameters, possibility to obtain discontinuities in the decaying part, and zero value of the function first derivative at t=0+. Parametrs of the function are obtained by using Least-squares method (LSQM)

NOVEL APPROACH TO MODELLING OF LIGHTNING CURRENT DERIVATIVE

A new approach to mathematical modelling of lightning current derivative is proposed in this paper. It builds on the methodology, previously developed by the authors, for representing lightning currents and electrostatic discharge (ESD) currents waveshapes. It considers usage of a multi-peaked form of the analytically extended function (AEF) for approximation of current derivative waveshapes. The AEF function parameters are estimated using the Marquardt least-squares method (MLSM), and the framework for fitting the multi-peaked AEF to a waveshape with an arbitrary number of peaks is briefly described. This procedure is validated performing a few numerical experiments, including fitting the AEF to single- and multi-peaked waveshapes corresponding to measured current derivatives

Monitoring štetnih tvari u hrani

Prema pozivu Upravnog odjela za zdravstvo, socijalnu skrb i rad prijavili smo nekoliko programa iz javno-zdravstvenih potreba u Istarskoj županiji za 2005. godinu: a) Program praćenja sadržaja metala (Pb, Cd) u krumpiru, kupusu, salati zelene tržnice Istre b) Program praćenja sadržaja histamina u plavoj ribi u ribarnicama Istre c) Program praćenja mikrobiološke ispravnosti „zdrave hrane“ (žitarice, sušeno voće, mlinski proizvodi i njihove mješavine iz prometa (trgovine, zelene tržnice) Istre