Joze Pihler

Artificial Neural Network Applied for Detection of Magnetization Level in the Magnetic Core of a Welding Transformer

This paper deals with the detection of saturation in the magnetic core of a welding transformer which is a part of a middle-frequency direct current (MFDC) resistance spot welding system (RSWS). It consists of an input rectifier, which produces dc bus voltage, an inverter, a welding transformer, and a full-wave rectifier that is mounted on the output of a transformer. During normal RSWS operation welding transformers magnetic core can become saturated due to the unbalanced resistances of both transformer secondary windings and different characteristics of output rectifier diodes, which causes current spikes and over-current protection switch-off of the entire system. In order to prevent saturation of the transformer magnetic core, the RSWS control must detect that the magnetic core is approaching the saturated region. The aim of this paper is to present a reliable method for detection of magnetic core saturation that does not require an additional sensor. It is based on the artificial neural network (ANN). Its input is the measured primary current of the welding transformer. The applied ANN is trained to recognize the waveform of the current spikes in the primary current caused by the magnetic core saturation, which is used for magnetization level detection.

Designing a New Post Insulator Using 3-D Electric-Field Analysis

Insulators are very important elements of electric power systems. This paper introduces an analysis of electrical conditions in the area between the conductor and the insulators upperfitting. The designing of new a composite post insulator is presented with the upperfitting made of insulating material. Previous composite post insulators have had upperfittings made of conducting material metal. 3D analysis of electric-field strength in the insulator and its surroundings are also given. The computation was carried out by using the OPERA Vector Fields program tool. The results of this analysis are presented for both-new and old versions of a composite post insulator. 3D analysis shows that the new version has up to five times lower magnitudes of electric-field strength.

Overvoltage Protection Using a Gas Discharge Arrester Within the MATLAB Program Tool

This paper deals with the modeling of a low-voltage gas discharge arrester using the MATLAB/Simulink program tool. The model is designed to enable a combination with other overvoltage protection system elements (metal-oxide varistor, supressor diode) in order to put a model of an integrated overvoltage protection system together. This model comprises all phases that may appear during the operation of a gas discharge arrester. Therefore, it consists of five main submodels, each of them representing one physical phenomenon. The results obtained by performing model analyses within the MATLAB/Simulink program tool were verified by laboratory tests with various voltage sources (lightning surge voltage, ac voltage, and combinations of them), performed on real gas discharge arresters.

Design of systems of covered overhead conductors by means of electric field calculation

Recently, in medium voltage overhead line systems, previously bare conductors are being replaced with conductors covered with a layer of insulation. Covered conductors enable an economical increase in operational reliability. At the current stage of development, there are several ways of replacing bare conductors with covered ones. Such a replacement also requires changing the accompanying line accessories, insulators, and line protection devices. The selection of the optimum combination of covered conductors and equipment has been done by means of electric field calculations. The optimization parameters have included the use of existing equipment to the maximum possible extent, new elements of equipment that have to be added, and the prevention of disturbances and failures in operation. Theoretical findings have been confirmed with laboratory tests on prototype combinations of covered conductors and the accompanying equipment.

The Influence of an Additional Substance in the Trenches Surrounding the Grounding Grid's Conductors on the Grounding Grid's Performance

In this paper, we present how the finite element method (FEM) can be utilized to analyze the influence of an additional substance in the trenches surrounding the grounding grids conductors on the grounding grids performance. For this purpose, we modified the preliminarily existent FIELD_GS program code in such a way that the additional substance in the immediate vicinity along the grounding grids conductors can be simulated. Different soil structures and various volumes of the additional substance in the soil have been analyzed to prove the suitability of surrounding the grounding grids conductors in trenches with the additional substance instead of strewing a whole grounding grids surface with the additional substance

Use of an optimization algorithm in designing medium-voltage switchgear insulation elements

Modern design of medium-voltage switchgear insulation elements is based upon the use of optimization methods. This paper presents an algorithm for the design of such elements using numerical calculations on the basis of the finite elements method in connection with evolution optimization methods. The use of differential evolution and evolution strategy algorithms is presented in the case of modeling a medium-voltage post insulator, the secondary function of which is voltage indication. A comparison between these two algorithms is also presented. The task of both optimization algorithms is to find an adequate capacitance of the voltage divider and the optimal distribution of electric field strength. All other requirements and constraints that have to be taken into consideration in the design of insulation elements are also included in the algorithm

Application of the Hybrid Multiobjective Optimization Methods on the Capacitive Voltage Divider

This paper presents application of multiobjective optimization methods on a capacitive divider finite element model. Modeling is based on the differential evolution algorithm (DE), including the concept of the Pareto nondominance. Through calculations, this concept allows differential evolution algorithm variation in order to achieve uniformly distributed results on the Pareto front, including the lowest population size as possible. Selection step, as a part of the differential evolution method, is properly modified to improve the convergence of the algorithm. The entire research leads to a hybrid algorithm development.

Mathematical Model of a Gas Discharge Arrester Based on Physical Parameters

This paper deals with a mathematical model of a gas discharge arrester, developed within the Matlab/Simulink program environment on the basis of physical and mathematical parameters. The model includes important physical phenomena regarding a gas discharge arrester, such as its overvoltage causing triggering, discharge processes, electric arc, and a possible repeated dielectric breakdown in gas due to the heat released from the arc to the gas. This paper includes computations for the operating conditions of a gas discharge arrester connected to an ac circuit. The computing results are compared with those measurements of electrical quantities performed on a gas discharge arrester.

Determining a Gas-Discharge Arrester Model's Parameters by Measurements and Optimization

This paper deals with the parameter determination procedure of a gas-discharge arresters (GDA) model. As the accuracy of the model depends on its parameters, the goal of this procedure is to determine adequate parameter values so that the models performances match the real device behavior as much as possible. In order to achieve this goal, differential evolution (DE), a stochastic optimization algorithm, is included in the determination process. The main task of the DE algorithm is to vary the models parameters during the optimization process, thus minimizing the difference between the measured and model-calculated current and voltage time behavior. An accurate GDA model has been obtained on the basis of measurements on a single GDA test object. This model is relevant and suitable for a series of GDA devices as the agreement between their measured and model-calculated voltage and current time behavior is excellent.

Potential Control Inside Switch Device Using FEM and Stochastic Optimization Algorithm

This paper describes the impact of selected insulation elements and the surrounding material, on the magnitude and distribution of electrical potential in a switch device. The procedure is based on finite element method numerical analysis and stochastic optimization algorithm of differential evolution (DE). The optimal selection of mutually independent insulation materials has an impact on the control of potential and, consequently, on dielectric strengths, both inside the bushing and in other switchgear elements. Two different methods are used for an extension of the multiobjective optimization of the problem. The entire modeling procedure also includes optimization of the bushings geometrical shape