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The purpose of this paper is to present a mathematical model for studying the effects of the interconnection through bare‐buried conductors (BBC) of the secondary substations' earthing system of an urban area.

The developed methodology is based on three main points: the solution of the transmission lines' equations for the formulation of a lumped parameters model of a BBC considering the conductive effect; the division of the distribution network into simpler sub‐systems; and the calculation of all the voltages and currents of the medium voltage (MV) network and of the earthing systems using a multiport approach.

The methodology has been applied to various situations giving precious information on the behaviour of the earthing systems interconnected by means of BBC in presence of conductive effect. The results of the simulation allow to quantify the reduction of the dangerous voltages appearing during an earth fault, in presence of interconnection between the secondary substations' earthing systems, realized by means of BBC.

Some factors can influence the precision of the methodology. Indeed, for a correct simulation of the system it is necessary to know several electrical and geometrical parameters, among all the resistivity of the soil that, often, is known with a large degree of uncertainty.

Utilities are quite interested in this topic. The study of interconnected earthing systems in MV networks with the purpose of identifying safe extended areas named global earthing systems (GES) has important management and economic consequences.

The paper presents an original lumped parameters model of the BBC, able to simulate these elements with a high accuracy, also in presence of the conductive effect, and that can be easily included in the more general model of a distribution line, in order to perform the analytical study of the GES in MV networks. The model proposed allows one to overcome the limits of the application to the MV networks of similar models present in the literature for the study of the same topic in the high‐voltage networks.

The purpose of this paper is to define a new methodology for studying interconnected earthing system inside unearthed medium voltage (MV) networks.

The developed methodology is based on the division of the MV network into simpler sub‐systems and its resolution using a multiport approach.

The methodology has been applied to various situations giving precious information on the behaviour of the interconnected earthing systems. The comparison between the results of the simulations and measurements done on a really existing network has shown that the methodology is able to provide accurate results.

Some factors can influence the precision of the methodology. Indeed, for a correct simulation of the system it is necessary to know several electrical and geometrical parameters, often obtainable with difficulty.

Utilities are quite interested in this topic. The study of interconnected earthing systems in MV networks with the purpose of identifying safe extended areas named Global Earthing Systems has important management and economic consequences.

The paper presents a new analysis methodology applicable to MV networks that surpasses the limits of the analysis methodology generally applied for the study of the same topic in high voltage networks.

The purpose of this paper is to present a method to model earthing systems subjected to lightning strikes with a one‐dimensional moment method. This paper was conducted because an accurate method to model earthing systems subjected to lightning strikes, was deemed necessary. To name a few examples of relevant situations: supply stations of railway systems, from which also critical signalling infrastructure is fed, earthing systems of cellular phone basestations, located in the vicinity of high‐antenna towers, prone to lightning strikes, and gas and oil pipelines. There exist already methods to solve this problem, based on circuit theory, but the electromagnetic method of this work is based directly on Maxwell's equations and therefore more accurate.

The earthing electrodes and meshes are represented as wire scatterers. First, the method is outlined for scatterers in a single medium. Next, the method is extended to model to presence of the soil‐air interface layer. An approximate technique, known as the modified image theory, is used to account for the vicinity of the soil. Finally, a second extension is given so that cables without metal sheets which are in the vicinity of the earthing systems, can be included in the model. Thereafter, it is described how the method can be used to calculate the effects of lightning strikes on earthing structures, and finally a validation of the method is presented.

The method is validated by applying it to simple situations which can also analytically be calculated, and by applying it to earthing structures for which the transient voltage was measured or calculated with circuit methods. A good agreement is seen. However, the method is computationally very expensive.

In order to account for the influence of the air‐ground interface, an approximate method was used: the modified image method, and not the exact Sommerfeld theory. This was done because of its simplicity and in order to speed up the calculation process. Furthermore, cables can be included in the model, but they must be of simple structure: a cylindrical core, surrounded by an insulating cladding.

A few authors have already described this method to simulate lightning strikes on earthing systems. However, in this paper, a new and easy model for underground cables in the vicinity of earthing systems is presented.

The purpose of this paper is to discuss two evaluation methods of single pole auto-reclosing process effectiveness in HV transmission lines. Secondary arc current and recovery voltage results obtained by load flow calculation are compared to the results obtained by the time domain simulations. Moreover, a nonlinear secondary arc implementation is presented.

A computer simulation studies were performed using DIgSILENT PowerFactory® software to analyse phenomena during single phase to earth short circuit and during single pole circuit breaker opening. Possibilities of electric arc extinction for different earthing solutions of shunt reactors were examined.

The authors indicate, that precise representation of secondary electric arc in power system studies could lead to different conclusion than analysis carried out on simplified arc models. Recommendations for line construction (i.e. earthing reactor installation) and line operation (i.e. prolongation of dead time during auto-reclosing) based on time domain simulations are less restrictive than resulting from the traditional steady-state calculation approach.

An implementation of mathematical model of nonlinear secondary arc for DIgSILENT PowerFactory® software is presented. The model could be used during the process of design of HV transmission line, to assess its proper operation, to calculate dead time during single pole reclosing or to evaluate the necessity of installing additional earthing reactors.

The purpose of this paper is to estimate influence of the pillar concrete foundation approximated by a semiconducting semi‐sphere on the pillar grounding system.

Unknown current distributions and impedance of pillar grounding system, which consists of a ferro armature modelled as a single electrode inside concrete foundation, ring electrode and two earthing conductors, are determined in this paper. Concrete foundation is approximated by a semi‐spherical semiconducting inhomogeneity. The expressions for electric scalar potential are formed using the quasi‐stationary image theory, including a recently proposed Green's function for the point source in the presence of a semiconducting sphere. Based on the quasi‐stationary antenna model, unknown currents are determined solving the system of integral equations using the moment method and polynomial approximation for current distributions.

The influence of inhomogeneity is not negligible for real values of specific conductivity of the inhomogeneity domain. The same goes for earthing conductor influence, especially the one on electric scalar potential distribution on the ground surface.

Besides the analyzed system, the model is applicable for solving for example a grounding system in the vicinity of large holes in the ground (pond and small lake) filled with water, treated as semi‐sphere or near vertical container (silage and reservoir) having semi‐spherical basis with a lower one buried in the ground.

Obtained results give possibility to analyze influence of semiconducting ground inhomogenities, which can be treated as semi‐spherically shaped ones, on grounding system. It results in better accordance of projected and real grounding system's characteristics.

This paper aims to describe a numerical procedure for approximating the potential distribution for a harmonic current point source, which is either buried in horizontally stratified multilayer earth, or positioned in the air. The procedure is very efficient and general. The total number of layers and the source position in relation to the medium model layers are completely arbitrary.

The efficiency of the computation procedure is based on the successful application of the numerical approximation of two kernel functions of the integral expression for the potential distribution within an arbitrarily chosen layer of the medium model. Each kernel function of the observed layer is approximated using a linear combination of 15 real exponential functions. Using these approximations and the analytical integration based on the Weber integral, a simple expression for numerical approximation of potential distribution within boundaries of the observed medium layer is given. Potential retardation is taken into account approximately.

The numerical procedure developed for the approximation of potential distribution for a harmonic current point source, which is positioned arbitrarily in air or in horizontally stratified multilayer earth, is efficient, numerically stable and generally applicable.

Numerical model developed for the harmonic current point source is the basis of a wider numerical models for computation of the harmonic and transient fields of earthing system, which consists of earthing grids buried in horizontally stratified multilayer earth and metallic structures in the air.

This is efficient and numerically stable frequency dependent harmonic current point source model. Potential retardation, which has been neglected at the first step of the approximation, is subsequently added to the potential expression in such a way that the Helmholtz differential equation has been approximately solved without introducing the Sommerfeld integrals.

April 18, 1972 Negligence — Contributory negligence — Damages — Apportionment — Plaintiffs minor contributory negligence — Whether to be disregarded — Law Reform (Contributory Negligence) Act, 1945 (8, 9 & 10 Geo. VI, c. 28) s. 1(1).

IT IS generally agreed that practical work has a vital part to play in the training of craft apprentices. While it may be argued that the apprentice has opportunities for learning the practical aspects of his chosen craft while at work, nevertheless the opportunity for carrying oat a wide variety of work is not always available. This situation often arises in the case of electrical craft students, as many electrical contracting firms are small concerns and are unable to provide melt apprentices with the wide variety of experience which is so desirable.

The aim of this fieldwork was the study of the effect of 50Hz AC, induced by high‐voltage power lines, on the cathodic protection system of a natural gas pipeline. The effectiveness of cathodic protection was checked through in situ long‐term monitoring and analysis of pipeline electrical parameters. The results gave an insight into the problems of the cathodic protection system operation, caused by AC interference. An AC and DC potential interdependence was observed, that previously has hardly been reported, and was scrutinized in relation to cathodically protected pipelines. The effects of the AC‐interference and low frequency DC potential fluctuations, as well as the potential deviations from the protection potential, are examined. These phenomena are associated with corrosion susceptibility and difficulties in obtaining reliable cathodic protection measurements.

Any electrical installation which is designed correctly, installed to a good standard of workmanship and maintained regularly should give many years of trouble‐free service. This paper assumes that the first requirement has been met and sets out the inspection and test procedures which are considered necessary to ensure that the two latter requirements are also satisfied. It is, however, concerned only with installations not exceeding low voltage.