What is earth resistivity in electricity?
Release time:
2021-11-12
What is earth resistivity?
The "earth resistivity" is the basic parameter affecting the earth resistance of an electrode system and is expressed in ohms-cm. However, it is not advisable to test the electrode earth resistance by calculating the actual value of the surface resistivity.
Earth resistivity:
The measurement of earth resistivity can easily be used in geophysical surveys - to find mineral sources, clays and water-bearing gravels beneath the earth's surface.
You can also use this indicator to assess bedrock depth and glacial drift density. Ground resistivity tests can also be used to find better locations and depths for low-resistance electrodes.
For example, these experiments are carried out when building a new electrical installation; a power station, substation, transmission tower or central office telephone.
The earth resistivity can then be used to indicate the degree of corrosion expected in underground pipelines for water, oil, gas and air.
In general, corrosion tends to increase where resistivity values are low. A good guide to installing cathodic protection is this type of information.
Factors that can change the small earth resistance, but first consider three factors that may change the specification of the earth electrode from year to year: the size of the plant or other electrical installation may increase.
In addition, increasingly large new plants are still being built. These changes in earth electrodes create different requirements. What was once a suitably low earth resistance may become an obsolete "norm".
As facilities add more modern and sensitive computer-controlled equipment, the problem of electrical noise is magnified. Since noise does not affect crude oil, older equipment may cause daily problems with newer equipment.
As more and more non-metallic pipes and conduits are installed underground, such installations are becoming less reliable as effective low-resistance earthing connections.
The groundwater level is gradually dropping in many locations. Earthing electrode systems that were previously effective for about a year may have a high resistance in dry soils.
These considerations emphasise the value of an active routine earthing test programme, which, only after completion, is not sufficient to test earth resistance.
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