Ioannis F. Gonos

Estimation of multilayer soil parameters using genetic algorithms

A methodology has been proposed according to which, after carrying out a set of soils resistivity measurements, one can compute the parameters of the multilayer earth structure using a genetic algorithm (GA). The results provided by the GA constitute the indispensable data that can be used in circuital or field simulations of grounding systems. The methodology, developed on the base of the PC Opera software package, allows to proceed toward a very efficient simulation of the grounding system and an accurate calculation of potential on the grounds surface.

Influence of large-scale installation of energy saving lamps on the line Voltage distortion of a weak network supplied by photovoltaic station

The aim of this research is to calculate and analyze the harmonic distortion extent caused in weak low-voltage networks due to a possible large-scale installation of the widely spread compact fluorescent lamps (CFLs). The research uses data from laboratory measurements of the produced harmonic currents by CFLs, as well as field measurements of the harmonic content and other characteristic measurements of the electric network of a small Greek island, which is supplied by an autonomous photovoltaic (PV) station. The PV station is also a harmonic generator by itself. This fact combined with other highly nonlinear loads-such as CFLs-causes serious problems at the network power quality as undesirable harmonic components are induced. The whole network is simulated and three scenarios of CFL installation extent are considered, so that the harmonic flow analysis reveals the influence in the power quality. It is examined whether this weak low-voltage electric network is able to keep the total harmonic distortion factor at all nodes under 8%, as more and more CFLs are installed. The conclusions drawn from this analysis are important and must be taken into account in every electric network design.

Stability of multidimensional systems using genetic algorithms

The study of the stability of m-dimensional systems is a difficult one especially when m /spl ges/ 3. There exist only a few results in the literature and unfortunately, there does not exist any practical criterion. In this work, the stability of an m-dimensional system is dealt as a minimization problem of the absolute value of its characteristic polynomial over the boundaries of its variables (i.e., on the m unit circles). This minimization problem is solved by using genetic algorithms (GAs). Using GAs we obtain, in general, better results than other methods of minimization (numerical techniques, neural networks, etc.). Numerical examples are presented.

Probability of backflashover in transmission lines due to lightning strokes using Monte-Carlo simulation

A method, which estimates the lightning performance of high voltage transmission lines based on the Monte-Carlo simulation technique, is described in this paper. The average number of faults which occur in a transmission line, dividing them in single-phase and three-phase faults, as well as the average grounding resistances of the transmission lines are calculated. The method is applied, on several operating Greek transmission lines, showing good correlation between predicted and field observation results. The proposed method can be used as a useful tool in the design of electric power systems, aiding in the right insulation dimensioning of a transmission line.

A genetic algorithm approach to the problem of factorization of general multidimensional polynomials

In this paper, a solution to the problem of the multidimensional (m-D) polynomial factorization is attempted by using genetic algorithms (GAs). The proposed method is based on an appropriate minimization of the norm of the difference between the original polynomial and its desirable factorized form. Using GAs, we can obtain better results than with other methods of minimization (numerical techniques, neural networks, etc.). The present methodology, which can also be used for every type of m-D factorization, is illustrated by means of a numerical example.

Arbitrary waveform generator for harmonic distortion tests on compact fluorescent lamps

Abstract This paper presents an experimental method to perform tests on compact fluorescent lamps operated with distorted voltage waveform conditions. The voltages used for the tests are obtained from an arbitrary waveform generator. It consists of a computer, a multifunction card and the software package. The characteristics of the voltage are entered from the computer that loads the required waveform into the card. The output of the card is driven to a voltage amplifier to supply the lamps. Samples of the voltage across the load and of the circulating current are recorded and transferred to the computer for harmonic analysis. The user supervises the tests through several virtual instruments that have been developed especially for this application. The system facilitates the performance evaluation of various appliances for distorted supply voltages. The cost of the system is very low compared with a conventional system consisting of an arbitrary waveform generator, a digital oscilloscope, a spectrum analyzer or/and a computer for harmonic analysis and a true rms multifunction meter. The experimental results show that the distribution of the harmonics of some lamp types does not alter linearly under distorted supply voltages.

Measurement of the electric field radiated by electrostatic discharges

The aim of this work is the investigation of the transient electric field radiated by two different commercial generators of electrostatic discharges for various charging voltages. Measurements of the electric field generated by contact electrostatic discharges have been conducted a few centimetres away from the discharge point. In this paper the current transducer, which is used for the measurement of the discharge current, is mounted on a grounded metal plane. It is the first time that measurements of the electric field have been conducted along three different directions in relation to the electrostatic discharge generator. Measurements prove that each generator produces a different transient electric field, which affects the equipment that is tested in a different way. Also, each generator produces a different electric field depending on the orientation of the generator. Finally, comparisons of the electric field for both generators and useful conclusions for the decrease of the electric field are presented.

Estimation of multi-layer soil parameters using genetic algorithms

Summary form only given. In this paper a methodology has been proposed, according to which, after carrying out a set of soils resistivity measurements, one can compute the parameters of the multi-layer earth structure using a genetic algorithm. The results provided by the genetic algorithm constitute the indispensable data that can be used in circuital or field simulations of grounding systems. The methodology, developed on the base of the PC Opera software package, allows to proceed towards a very efficient simulation of the grounding system and an accurate calculation of potential on the grounds surface.

Harmonic distortion in electric power systems introduced by compact fluorescent lamps

The purpose of this paper is the investigation of the harmonic distortion introduced by the compact fluorescent lamps to the distribution systems. The results of some measurements on compact fluorescent lamps (CFL) and on self-ballasted fluorescent lamps (SBL) of various wattages are presented. Some of the most important electrical characteristics (voltage, current and power factor) were measured by a data acquisition system. The harmonic spectrum and the total harmonic distortion (THD) of the lamps were calculated using Fourier analysis of the recorded current waveforms. The measurements were performed with supply voltage other than the nominal one in order to determine the dependence of the THD variation upon the mains supply voltage. From these measurements, conclusions concerning the problem of harmonics are drawn.

Influence of compact fluorescent lamps on the power quality of weak low-voltage networks supplied by autonomous photovoltaic stations

The principal goal of this research is to determine the influence of compact fluorescent lamps (CFLs) harmonics on the voltage distortion of a weak electric network supplied by an autonomous photovoltaic (PV) station. The total harmonic distortion factor at all points of the electric network must be under 5%. The power electronics of a PV station and other highly non-linear loads such as CFLs induce undesirable harmonic components and cause serious problems at the network power quality. For that reason, a specific methodology is developed, which uses data from field measurements of the harmonic content and other characteristic measurements of the PV station supplied electric network of the island of Arki. Then, after simulating the whole network, a harmonic flow analysis takes place showing the extent that CFLs influence the power quality. The conclusions drawn from this analysis are important and must be taken into account in every electric network design.