Jovan Trifunovic

The algorithm for determination of necessary characteristics of backfill materials used for grounding resistances of grounding loops reduction

Various backfill materials are used with the aim to reduce grounding resistance of grounding systems to the desired values. The algorithm for determination of a proper combination of features a backfill material needs to possess in order to successfully perform this task is developed and presented. It is based on the numerical analysis of the results obtained with finite-element method modelling of the considered grounding system, surrounding soil, backfill material and imperfect contact. As an example, the developed algorithm is applied on two grounding loops (one conventional and the other backfilled with bentonite suspension) embedded in a two-layer soil. The results obtained with the application of the proposed algorithm can be used as guidance for the researchers who are looking for new suitable low cost backfill materials.

An Algorithm for Estimating the Grounding Resistance of Complex Grounding Systems Including Contact Resistance

In cases where the grounding system is buried in soils characterized by poor contact with the electrodes (e.g., karst and sandy terrains), the contact resistance frequently represents a dominant component of the total grounding resistance. In such cases, estimation of the grounding resistance by conventional formulas given in the literature is useless, because they do not take into account the contact resistance. An algorithm for estimating the total grounding resistance of complex grounding systems, with the contact resistance included, was developed and presented in this paper. The algorithm is applied to a grounding system of a typical 110-kV transmission line tower used in the Serbian transmission power system. Simple formulas by which the total grounding resistance of the analyzed grounding system can easily be calculated are also derived. The obtained results are validated using 3-D finite-element method (FEM) modeling and a practical method from the literature. It was shown that the total grounding resistances determined by the proposed algorithm deviate less than 4% from those obtained by FEM calculations. Since the proposed algorithm is general and can be applied to any grounding system, it represents a powerful tool for estimating the grounding resistance in an early stage of the design process.

Influence of process parameters in pulse plasma nitriding of plain carbon steel

Abstract Glow discharge nitriding is widely used to improve the mechanical characteristics of steel components. This treatment produces a modified surface layer, consisting of an outer compound zone and an inner diffusion zone. The compound zone (white layer) is the first zone and therefore, is the contact surface layer. It is of particular interest for establishing the exploitation features of engineering components exposed to the wear and corrosion. It is important to analyse the mechanical and tribological features of this layer. With the aim of optimising the nitriding process and gaining an insight for further research, experimental studies of the pulsed plasma nitriding of plain carbon steel grade DIN C45 (AISI C1043) were carried out, using a pulsed direct current glow discharge. The influence of gas composition, temperature, treatment time, duty cycle and frequency on compound layer thickness and microhardness has been investigated. Five experiments were performed. In each experiment, one of the process parameters was varied while the others were kept constant. The characteristics of the nitride surface layers were studied by optical metallography, Vickers microhardness measurement as well as specially modified Calo test method. The results obtained could be useful in optimising of the nitriding process and computer process control.

A Mathematical Method for Determining Optimal Quantity of Backfill Materials Used for Grounding Resistance Reduction

During installation of grounding system, which represents a significant part of any electrical power system, various backfill materials are used for grounding resistance reduction. The general mathematical method for determining an optimal quantity of backfill materials used for grounding resistance reduction, based on the mathematical tools, 3D FEM modeling, numerical analysis of the obtained results, and the “knee” of the curve concept, as well as on the engineering analysis based on the designer’s experience, is developed and offered in this paper. The proposed method has been tested by applying it to a square loop enveloped by a backfill material and buried in a 2-layer soil. The results obtained by the presented method showed a good correlation with the experimentally obtained data from literature. The proposed method can help the designers to avoid the saturation areas in order to maximize efficiency of backfill material usage.