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The nature and principle of grounding resistance

time:2021/5/7   source:华天电力  reading:249 time

The nature of the ground electrode


The nature of the ground electrode In fact, the resistance to the current passing through the ground electrode has three components:


The resistance of the electrode itself and its connection.


The contact resistance between the electrode and the adjacent soil.


The resistance of the surrounding earth.


Electrode resistance: Rods, tubes, metal blocks, structures and other equipment are usually used for grounding. These are usually of sufficient size or cross-section so that their resistance is negligible in the total resistance.


Earth Resistance Tester.png


Electrode-ground contact resistance: This is much smaller than you think. If there is no paint or grease on the electrodes and the grounding is firm, the contact resistance can be ignored. The rust on the iron electrode has little or no effect, but if the iron pipe rusts, the part below the fracture is invalid as part of the ground electrode


The resistance of the surrounding earth: The electrodes driven into the earth of uniform resistivity radiate current in all directions. It is believed that the electrode is surrounded by a large crust of equal thickness. The ground shell closest to the electrode naturally has the smallest surface area and therefore the largest resistance


Principles involved in grounding resistance testing


In theory, the ground resistance of any electrode system can be calculated from a formula based on the general resistance formula:


R=ρLA


Where ρ is the resistivity of the earth, in ohm-cm, L is the length of the conductive path, and A is the cross-sectional area of the path. All these formulas can be simplified by the following assumption: Assume that the earth’s resistivity is uniform throughout the entire volume of soil under consideration.

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