Amélioration des valeurs de résistance de terres de masses Lower (reduce) the earthing resistance or Improve the earthing conductivity
Explanation: I wouldn’t talk about 'Améliorer les valeurs de résistance des terres' but about 'Réduire la résistance de mise à terre' or `'Améliorer la conductivité de la mise à terre' as 'Ameliorer' means to reduce the resistance, or to improve the conductivity, what every electrician knows, but not every laymen. Overview of Method for Reducing Grounding Resistance of Substation Grounding System Abstract. In order to reduce the grounding resistance of the grounding device, people takes various measures, as shown below: expanding the grounding grid area, exterior grounding, utilizing natural grounding, deep well grounding, local soil replacement and the like. https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd... Importance of Proper Grounding Just as it’s important to ground equipment and panels for lower voltages (50 – 600 VAC) per NEC 250 for proper grounding and bonding in order to reduce electric shock for human safety and proper equipment protection, likewise, it’s extremely important to ensure proper substation grounding is performed due to the higher voltages and increases in fault current. Since electrical current flows through the path of least resistance or to ground, it’s important to maintain a proper ground. The NEC 250 recommends the grounding of panel and equipment to maintain a resistance of 25-ohms or less. In substations the grounding should maintain a resistance of 1 to 5-ohms, depending on size and voltage levels. The main goal of grounding is to ensure that the path of least resistance for electrical current is not through personnel or equipment. Unlike grounding for lower voltage panels and equipment, designing a proper substation grounding system requires a copper grid mesh to be installed underground at a minimum of 18 inches below grade. https://3phaseassociates.com/importance-of-an-adequate-subst... Ground Potential Rise (GPR) The substation earth grid is used as an electrical connection to earth at zero potential reference. This connection is not ideal due to the resistivity of the soil within which the earth grid is buried. During typical earth fault conditions, the flow of current via the grid to earth will therefore result in the grid rising in potential relative to remote earth to which other system neutrals are also connected. This produces potential gradients within and around the substation ground area - this is defined as ground potential rise or GPR. The GPR of a substation under earth fault conditions must be limited so that step and touch potential limits are not exceeded, and is controlled by keeping the earthing grid resistance as low as possible. https://www.cablejoints.co.uk/sub-product-details/cable-sock... This is equivialent to the equipotential bonding: Area Earthing and protection against electric shock / Electrical installations and equipment IEV ref 195-02-22 en equipotential bonding system EBS (abbreviation) interconnection of conductive parts providing equipotential bonding between those parts Note – If an equipotential bonding system is earthed, it forms part of an earthing arrangement. fr réseau équipotentiel, m interconnexion de parties conductrices, permettant d'assurer une liaison équipotentielle entre ces parties Note – Si un réseau équipotentiel est mis à la terre, il fait partie d'une installation de mise à la terre. https://www.electropedia.org/iev/iev.nsf/display?openform&ie... Domain: 6826 electronics and electrical engineering [ INDUSTRY ] Definition: an electrical connection putting various exposed conductive parts and extraneous conductive parts at a substantially equal potential Term: equipotential bond Reliability: 3 Term in context: 'The two main components of an earthing system are equipotential bonding and formal earth electrodes. Equipotential bonds seek to minimise the potential difference experienced across exposed metallic conductive parts by connecting them together.' Language usage: The process of installing equipotential bonds is known as 'equipotential bonding'. Definition:liaison électrique mettant au même potentiel, ou à des potentiels voisins, des masses et des éléments conducteurs Term: liaison équipotentielle Reliability: 3 https://iate.europa.eu/entry/result/1367077/en-en-fr-la-mul Hence, I propose the following translation in the context: - Identify MV and LV branches by placing labels on the cables; - Pruning of certain trees near the MV/LV power lines; - Install two (2) sets of 36 kV 25 A MV fuses (P 10 and P11); - Lower (reduce) the ***** earthing resistance of the substations supplying town A and town B; or - Improve the earthing conductivity of the substations supplying town A and town B; Note: If the translation is addressed to USA, please replace 'earthing' by 'grounding'.
-------------------------------------------------- Note added at 1 day 20 hrs (2021-04-05 13:29:13 GMT) --------------------------------------------------
In order the highlight the different aspects of earthing systems and soil electrical conductivity vs. soil resistivity I add corresponding articles: An earthing system (UK and IEC) or grounding system (US) connects specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes.[1] The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. (Note: Canada uses the IEC terminology) : In high-voltage networks (above 1 kV), which are far less accessible to the general public, the focus of earthing system design is less on safety and more on reliability of supply, reliability of protection, and impact on the equipment in presence of a short circuit. Only the magnitude of phase-to-ground short circuits, which are the most common, is significantly affected with the choice of earthing system, as the current path is mostly closed through the earth. Three-phase HV/MV power transformers, located in distribution substations, are the most common source of supply for distribution networks, and type of grounding of their neutral determines the earthing system. followed by description of 5 different earthing systems : Soil resistance is a major aspect in the design and calculation of an earthing system/grounding installation. Its resistance depends on the efficiency of the removal of unwanted currents to zero potential (ground). The resistance of a geological material depends on several components: the presence of metal ores, the temperature of the geological layer, the presence of archeological or structural features, the presence of dissolved salts, and contaminants, porosity and permeability. https://en.wikipedia.org/wiki/Earthing_system#Other_terminol... Soil electrical conductivity is an indirect measurement that correlates very well with several soil physical and chemical properties. Electrical conductivity is the ability of a material to conduct (transmit) an electrical current and it is commonly expressed in units of milliSiemens per meter (mS/m). Alternatively, electrical conductivity measurements can be expressed in deciSiemens per meter (dS/m), which is 100 times greater than milliSiemens per meter. (Note: conductivity [S] = 1/resistivity = [ 1/Ω], ): There are two different types of sensors that can measure electrical conductivity – a contact sensor and a noncontact sensor. : Usually, two to three pairs of coulters are used. One pair provides electrical current to the soil while the others measure the voltage drop between them and use that drop to calculate electrical conductivity. : Figure 2. A contact soil electrical conductivity measuring system Figure 3. Electromagnetic induction measures soil electrical conductivity using noncontact sensors https://www.lsuagcenter.com/Nr/Rdonlyres/E57e82a0-3b99-4dee-... For engineering design purposes, as the electrical conductivity of soils is a function of its geotechnical properties (soil mineralogy, particle size distribution, void ratio, pore size distribution, pore connectivity, degree of water saturation, pore water salinity, and temperature), it is important to determine a robust quantitative relationship between the electrical resistivity of soils and its geotechnical properties, … https://www.lsuagcenter.com/Nr/Rdonlyres/E57e82a0-3b99-4dee-... Abstract–The accurate measurement of soil resistivity and earthing system resistance is fundamental to electrical safety. However, geological and meteorological factors can have a considerable effect on the accuracy of conventional measurements and the validity of the measurement methods. : Seasonal variations will also affect soil resistivity, primarily due to changes in soil moisture content. These dynamic variations may impact significantly on earthing measurements, depending on both the nature of the soil and underlying rock and the type of earthing system. : In soil resistivity testing, perhaps more correctly called earth resistivity testing, especially where the soil cover is thin, there are several classical electrical measurement techniques [5,10]. As shown in Figure 1, the Wenner technique is commonly used for earth resistivity testing in earthing investigations. … : To measure the earth resistance of a large earthing system it is necessary to use the Fall of Potential method [11]. With reference to figure 2, the Fall of Potential (FoP) method uses a four-terminal measurement principle. … https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.62...
-------------------------------------------------- Note added at 1 day 20 hrs (2021-04-05 14:04:13 GMT) --------------------------------------------------
Last item: The different earthing methods: To connect the metallic (conductive) Parts of an Electric appliance or installations to the earth (ground) is called Earthing or Grounding. In other words, to connect the metallic parts of electric machinery and devices to the earth plate or earth electrode (which is buried in the moisture earth) through a thick conductor wire (which has very low resistance) for safety purpose is known as Earthing or grounding. : The resistance of the earth continuity conductor is very low. According to IEEE rules, resistance between consumer earth terminal and earth Continuity conductor (at the end) should not be increased than 1Ω. : Components of Earthing System A complete electrical earthing system consists on the following basic components. • Earth Continuity Conductor • Earthing Lead • Earth Electrode : Earthing can be done in many ways. … Plate Earthing: In plate earthing system, a plate made up of either copper with dimensions 60cm x 60cm x 3.18mm (i.e. 2ft x 2ft x 1/8 in) or galvanized iron (GI) of dimensions 60cm x 60cm x 6.35 mm (2ft x 2ft x ¼ in) is buried vertical in the earth (earth pit) which should not be less than 3m (10ft) from the ground level. : Pipe Earthing: A galvanized steel and a perforated pipe of approved length and diameter is placed vertically in a wet soil in this kind of system of earthing. It is the most common system of earthing. : Rod Earthing it is the same method as pipe earthing. A copper rod of 12.5mm (1/2 inch) diameter or 16mm (0.6in) diameter of galvanized steel or hollow section 25mm (1inch) of GI pipe of length above 2.5m (8.2 ft) are buried upright in the earth manually or with the help of a pneumatic hammer. : Earthing through the Waterman In this method of earthing, the waterman (Galvanized GI) pipes are used for earthing purpose. Make sure to check the resistance of GI pipes and use earthing clamps to minimize the resistance for proper earthing connection. : Strip or Wire Earthing: In this method of earthing, strip electrodes of cross-section not less than 25mm x 1.6mm (1in x 0.06in) is buried in a horizontal trenches of a minimum depth of 0.5m. If copper with a cross-section of 25mm x 4mm (1in x 0.15in) is used and a dimension of 3.0mm2 if it’s a galvanized iron or steel. : https://www.electricaltechnology.org/2015/05/earthing-and-el... (Note: I miss the earthing mesh, buried inside the foundation and/or outside) 14.2. TYPE A – VERTICAL AND HORIZONTAL ELECTRODES Vertical and/or horizontal electrodes are used. There must be earth electrodes installed at the base of each down-conductor. A minimum of two electrodes must be used : 14.3. TYPE B – RING ELECTRODE While it is stated a requirement is to be a closed ring, encircling the structure, it is permitted to use conductors in the structure such as foundation earthing or permanently connected conductive metal items such as pipes and conduit as part of the ring. : 14.5. FOUNDATION EARTH ELECTRODES Concrete reinforced foundations can be used as earth electrodes and are considered to be of type B. http://electrik.info/lightning-protection-in-a-nutshell.pdf 3.7.2Earth Mats under foundations and floors Where the earth mat passes under concrete foundations or floors, the lowest earthing resistance as well as the minimal corrosion effect between copper and reinforcing bars is achieved if the 10 mm diameter copper rod is placed directly on top of the blinding, then cast in concrete by the foundation or floor. 3.7.3Structural Steelwork a. The steelwork structures in the transformer bays shall be connected to the earth mat in accordance with the relevant sheets of drawing 0.54/393. https://tenderbulletins.co.za/files/240-56356396_Earthing an... Note: All references cited above (not exhaustive) contains a lot of more interesting details for those who want to know how to proceed.
| Johannes Gleim Local time: 11:07 Works in field Native speaker of: German PRO pts in category: 189
|
|