Method of Locating Ground Fault in Low Resistance Grounding Distribution Network by Grounding Wire Current

Three-core cables are increasingly used in urban distribution networks. The shielding layer, armor layer of the three-core cable and the earthing electrode constitute the earth-electrode network. When a ground fault occurs, a regular ground wire current distribution is formed in the network. This paper analyzes the distribution law of ground current, and according to the distribution law, puts forward a kind of grounding fault location method of neutral point small resistance grounding grid, and finally designs and implements the grounding fault location system.

DEVELOPMENT AND MODELLING OF HIGH SPREAD CONDUCTIVITY EARTH ELECTRODES FOR COMPLEX EARTHING ARRANGEMENTS

The analysis of methods for calculating the electrical characteristics of earth electrodes in case of emergency currents of industrial frequency flowing through the elements of earthing arrangements is carried out. A method for improving complex earthing arrangements of electrical installations by optimization of their design parameters is proposed. The proposed method consists in installing an artificial earth electrode with an increased contact area of its surface with the ground, which makes it possible to increase the conductivity of earthing spreading. The use of these electrodes on the territory of projected or operating electrical installations ensures that the values of the normalized parameters of earthing arrangements are brought to permissible values. The use of the method given in the calculations of earthing arrangements requires the replacement of volumetric earth electrodes with a set of linear vertical electrodes. The design model is substantiated by equivalent electrical characteristics relative to the two-layer model of the electrical structure of the earth. The equivalent model was obtained by a given approximation of the electrical characteristics of a set of straight electrodes in the process of increasing their number to the equivalent characteristics of the reference model. In turn, the determination of the characteristics of the reference model was carried out directly by solving the boundary value problem for the potential satisfying Laplace equation using finite difference method. Theoretical investigations using induced potential method and methods of calculation of branched electric circuits with distributed parameters for calculation of electric field and resistance of the complex non-equipotential earth electrode in the ground with two-layer structure have been carried out. The developed electrodes of increased spread conductivity are mounted as experimental samples and are involved in the formation of the electrical characteristics of the earthing arrangements.

CORRECTION OF THE METHOD FOR MEASURING THE AMPLITUDES OF THE CURRENT OF THE IMPULSE ALONG THE LONG EARTH ELECTRODE

An improved method for measuring the amplitude reduction of the lightning current impulse as it flows from the beginning to the end of long horizontal earthing arrangement using ferromagnetic recorders has been substantiated. Two existing methods of pulse amplitude measurements at high voltages, the magnetic recording method and the method using a shunt, are used in justification. It is noted that in a number of cases it becomes necessary to determine the decrease in the pulse amplitude as it flows on a long object. This leads to the need to develop a method for performing such measurements. As an example, a long horizontal earth electrode was investigated when a lightning current pulse moves on it. Based on experimental studies in natural conditions, an improved method for measuring the decrease in the amplitude of the lightning current impulse along a long earth electrode is proposed. The proposed method has a measurement error not exceeding 10 %, and allows simultaneous measurements of the amplitude of the current strength at given points of the object, which can amount to tens or even hundreds. This method is implemented in a simple design and has an affordable manufacturing cost. The results of the experiments performed make it possible to recommend the corrected measurement method for practical use on existing electrical installations. The use of ferromagnetic recorders for recording and measuring the lightning current in areas of complex earthing arrangements is relevant for practical reasons, which include the possibility of measuring during a long wait and long-term storage of measurement results, does not require additional power sources and provides the possibility of synchronous measurements at various points of the grounding device. An important feature of the method is safety for technical equipment and personnel.

Optimal Design of the Vertical Earthing with Electrodes Arranged in Line

The design methods of earthing from standards recommend the choice of electrode lengths and propose that the distances between electrodes to be 1–3 times larger than their length. The number of electrodes is determined from the condition of achieving the design earth resistance, while the design ends with the choice of one of the variants. This paper presents the methodology for calculating the earthing system with cylindrical, vertical electrodes arranged in a line. The main variables are the length and the number of earth electrodes, as well as the distance between adjacent ones. Firstly, a set of technologically advantageous values for the earth electrode length is established (e.g., 10 values). For each value of the electrode length and different numbers of electrodes (e.g., 11 values), the distance between adjacent electrodes is determined (e.g., for 110 cases), which leads to the design value resistance. Finally, optimal solutions are identified based on the five optimal applied criteria. The proposed optimal criteria for earthing design are the footprint area, the total earthing volume, the total dispersion surface, the total metal mass, and the investment costs. Comparing the optimal solutions with other technically possible solutions clearly highlights substantial savings concerning space, material, and cost.