Analytical Approach for the Systematic Research of the Periodic Ferroresonant Solutions in the Power Networks

Ferroresonance is a complex and little known electrotechnical phenomenon. This lack of knowledge means that it is voluntarily considered responsible for a number of unexplained destructions or malfunctioning of equipment. The mathematical framework most suited to the general study of this phenomenon is the bifurcation theory, the main tool of which is the continuation method. Nevertheless, the use of a continuation process is not devoid of difficulties. In fact, to continue the solutions isolats which are closed curves, it is necessary to know a solution belonging to this isolated curve (isolat) to initialise the continuation method. The principal contribution of this article is to develop an analytical method allowing systematic calculation of this initial solution for various periodic ferroresonant modes (fundamental, harmonic and subharmonic) appearing on nonlinear electric system. The approach proposed uses a problem formulation in the frequency domain. This method enables to directly determine the solution in steady state without computing of the transient state. When we apply this method to the single-phase ferroresonant circuits (series and parallels configurations), we could easily calculate an initial solution for each ferroresonant mode that can be established. Knowing this first solution, we show how to use this analytical approach in a continuation technique to find the other solutions. The totality of the obtained solutions is represented in a plane where the abscissa is the amplitude of the supply voltage and the ordinate the amplitude of the system’s state variable (flux or voltage). The curve thus obtained is called “bifurcation diagram”. We will be able to then obtain a synthetic knowledge of the possible behaviors of the two circuits and particularly the limits of the dangerous zones of the various periodic ferroresonant modes that may appear. General results related to the series ferroresonance and parallel ferroresonance, obtained numerically starting from the theoretical and real cases, are illustrated and discussed.

Wind Energy Conversion Systems Adapted to the Tunisian Sites

The choice of a wind turbine for a given site is a very significant operation. It is advised to make an in-depth study on the characteristics of the aerogenerator and the implantation site before any installation of a wind farm for choosing well the system best adapted to the energy needs. The objective of this study is to sensitize the users of the wind energy on the various problems involved in the aerogenerator installation on any site and to provide a decision-making aid to the judicious choice of the wind system best adapted. The idea is to estimate, for a selected implantation site, the energy production and the operating time of several wind systems. We can thus select the aerogenerator best adapted by making a compromise between a maximum recovery of energy and a high time of production. The influence height of the aerogenerator on energy profitability is also studied. We apply this step to the twenty six Tunisian synoptic sites by implantation scenarios of seven wind systems of various nominal speeds in function of the height.