Ground Resistance Article. Introduction: The grounding system is an essential element. Allow for protective devices activation. Equalize the potential of conductive. Allow the lightning strike energy to. Reduce electromagnetic interferences. But the. correct measurement of this parameter needs to fulfill several. Physical nature of the earth resistance. The understanding of the earth resistance. According to its definition, resistors. Only one of the terminals is evident in. In order to find the second terminal. Earth Resistance is. Figure 2). The idea is that outside the earth volume. In order to justify the previous statement. Figure. 4). The current being injected in the earth. Each layer. offers a resistance to the passing current, which is proportional. Figure 1), and inversely. Earth resistance measurement. This is because an earth resistance can vary with changes in climate or temperature, and, as such.![]() The thickness is arbitrarily defined as thin enough. Really, the thickness is infinitesimal. In order to allow an easier physical visualization. The important concept to be observed. In figure. 4, it can be observed that surface S3 is much bigger than. S1. When the surface increases, the resistance. Calculations for the case of an hemispherical. In other words, the contribution. And as there is no resistance, there. Consequently, outside the. Measurement method: In order to measure the resistance, we. One of the terminals. E. The second one. Also ideal for large earthing systems by the considerable test. EARTH RESISTANCE INTRODUCTION. Principle of measurement Fig. 6 System earth resistance Rx Measuring current I When the bridge is balanced (Galvanometer current is zero). Earth/ground measurement guide. The earth resistance measurement described in this section6). Download as PDF, TXT or read online from Scribd. Flag for inappropriate content. Measuring Earth Resistance. Soil resistivity is a measure of how much the soil resists the flow of electricity. It is a critical factor in design of systems that rely on passing current through the Earth's surface. An understanding of the soil. In order to carry. H at that point. The second electrode will inevitably have. If we look at figure. Our objective is to measure electrode. E earth resistance. However, if a conventional resistance. E and H is carried out by measuring. E. The difference. H dimensions are very small in. E, so its contribution to the total resistance. The concept of . In such a case, all the volume that is outside. Fall- of- Potential Method. A third electrode S is used in order. H, The S rod is hammered at any point outside the E and H. Figure 6. This arrangement is known as Fall- of- Potential. Method and it is the most commonly used for the earth resistance.
The current circulates through. E and the auxiliary electrode H, and the. E and the third electrode S. This. voltage is the fall of potential that the test current produces. Rx, which in this way can. H rod. The 6. 2% rule Many publications that make reference. Fall- of- Potential Method indicate that, in order to. E and S must be the. E and H (figure. 7). This concept comes from a careful mathematical development. Dr. The first problem to be faced. Potential Gradients in the Earth. The Variability of Soils in Earthing Measurements. Earth resistance measurement. Besides, in urban areas it. Fortunately, by using the same calculations. Consider the segment joining E with. H and the straight line that intersects that segment at its. Then, multiplying the measured value by 1. It is also observed that as the voltage electrode. EH, the area where the measured. In Figure. 8, if the electrode S is hammered at any point outside. In order to evaluate. Dr. This is because an earth resistance can. If the grounding system approximates to. D is its diagonal (Figure. Imagine the segment EH that joins the. E with the auxiliary rod. H. At the middle point of that segment, draw an imaginary. Hammer the auxiliary rod S (potential. EH segment. Measure the earth resistance using. These. values are merely indicative, and the measured value does. D). A more detailed analytical study of the. Note. Auxiliary electrodes earth resistance. Current and potential auxiliary electrodes. As it has already. However, earth testers constructive limitations. Related to current electrodes, the limitation. A very high resistance of this electrode would. The IEC 6. 15. 57- 5 standard, specific for. It also requires the instrument to be able to determine. Several instruments carry this. Interferences When a grounding system resistance of. E and the potential electrode S appears due. The same happens. This is because the injected. The greatest challenge that. Earth tester faces is to be able to distinguish the. This distinction is easier to achieve. Where: Fg = Frequency of the current injected. Fi = Industrial frequency (5. Hz or 6. 0. Hz, depending on the country)N = Any integer greater than zero. Each manufacturer chooses an N value that. The 2. 70. Hz frequency has the peculiarity. N = 4 in the 6. 0 Hz regions. N = 5 in the 5. 0Hz region. Other adequate frequencies following. Hz, 5. 70. Hz, 6. Hz, 8. 70. Hz, 9. Hz. 1. 17. 0Hz, 1. Hz, 1. 47. 0Hz, 1. Hz, etc. The separation is carried out using high. A very adequate configuration is the. This model is equivalent to a highly. If the grounding. However, some grounding systems. In such a case, their behavior. For fault. currents the frequency will be low, of about 5. Hz. But. when it has to dissipate an atmospheric discharge current. Manuel. Jamie Leibovitch, R& D director of Megabras Industria Electronica. Ltda. Represented by Duncan Instruments Canada Ltd.
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