FAQs - Grounding Systems
- FAQs - Grounding Systems
FAQs - Grounding Systems
1) What is the need for grounding?
The basic objective of good earthing is to ensure the safety of life and property from shock and fire.
Lightning, Surges or Unintentional contact between an energized electric conductor and the metal frame or structure that encloses it or an insulation failure in electrical equipment etc., can cause dangerously high voltages in the electrical distribution system. Under such circumstances , grounding provides an alternative low impedance path and thereby minimizes damages.
A good and an efficient earth ensures that all parts of apparatus other than the live parts shall be at earth potential, ie zero at all times.
2) Do we need maintenance free earthing?
With the increased degree of sophistication in all equipments, the grounding system needs to be reliable over a long term to ensure safety and proper working of these equipments.
Besides, all industries are facing a shortage of manpower and as such it may not be possible to test the Earth Pits frequently. Also, in a lot of cases the Earth Pits may not be accessible after a few months / years due to various reasons. Further, in a running unit, disconnecting some Earth connections may warrant Shutdown. This coupled with the fact that the equipments are far more sensitive today make a clear case for adopting maintenance free earthing solutions in all scenarios.
3) How to calculate the resistance of an electrode when using the earth enhancement backfills?
The BS-7430 (after which the IS-3043 is modeled) provides a formula vide Clause No.8.5 Page 10 which is as below:
P is the resistivity of soil, in ohm metres (Ώ);
Pc is the resistivity of infill material, in ohm metres (Ώ);
d is the diameter of electrode, in metres (m);
D is the diameter of infill (Backfill), in metres (m);
L is driven length electrode, in metres (m);
The above formula specifically gives a weightage to the resistivity of the in-fill material. The lower the resistivity of the in-fill material, lower will be the overall earth resistance (this fact is mentioned in all standards like IS-3043, BS-7430 and IEEE-80 .The resistivity of our backfill material is less than 0.001 Ohm metre and thus , by using our special Backfill, the reduction in resistance between 30-60% over conventional earthing systems can be obtained for a given site conditionsbr
4) How will a Earth Pit of 4” bore dia help to lower the earth resistance?
As mentioned in all the standards like IEEE & BS etc, the inner shell of soil closest to the electrode comprising the bulk of the electrode ground resistance to remote earth. As per the Table given in IEEE No 9,The first 100 mm of the material accounts for approximately for 48% of the total resistance. Hence by having a highly conductive compound for 75 mm around the electrode, upto 48% of the total resistance can be controlled and this is the reason why a 4” bore hole filled with our Backfill product offer lower resistance to the tune of 35 to 50%.
5) Does the system need watering?
Regarding the need for watering there are several issues to discuss. First, the carbon-based compound itself does not require water (moisture) to conduct current since carbon conducts electronically. This can be readily demonstrated by placing the carbon compound (without one of the corrosion inhibitors present) in a soil box and measuring the resistivity. The second issue involves one of the corrosion inhibitors added to the compound which is water-soluble. In order for this inhibitor to function, moisture is required to dissolve the inhibitor. The inhibitor itself is non-conductive in undissolved form; therefore, it significantly increases the resistivity of the carbon compound until moisture is present. Once moisture is present the inhibitor readily dissolves, causes a surface reaction on the copper electrode to inhibit corrosion, and no longer affects the resistivity of the carbon backfill. Hence, the system needs watering only once (for activating the corrosion inhibitor) and thereafter does not rely on moisture for conductivity.
6) Although the compound offers low resistivity, the area surrounding the bore where there is no moisture still offers higher resistivity and may need watering .How to counter this?
The moisture in the soil around the electrode/backfill installation involves the conduction mechanism in the soil itself. The earth (soil) is basically made up of non-conductive minerals. (There are some rare conductive minerals such as magnetite, specular hematite, pyrite, carbon-graphite, and pyrrhotite.) Since most of the components are non-conductive, the only way current can flow in the soil is through the moisture in the soil. In other words, current flow in the earth is electrolytic through dissolved ions in the soil moisture. Therefore, if there is no moisture, the soil is non-conductive, and grounding cannot occur.
Since grounding can be accomplished even in relatively high resistivity dry soils, this means that some moisture is present. The amount of moisture does not have to reach saturation in order for the soil to become conductive. There only has to be sufficient moisture to coat individual mineral grains to provide a continuous bridge of moisture. As the volume of earth through which the current must flow gets very large, the amount of moisture in the soil (resistivity) becomes less important.
Further, the most important volume of earth that primarily determines the overall grounding resistance is the volume of earth near the grounding electrode. This is the primary reason why either a salt & charcoal or any other additives are used around the electrode. This point is also mentioned in the existing version of IS 3043 – Pg 19 cl 9.1.1- “To obtain a low overall resistance, the current density must be as low as possible in the medium adjacent to the electrode”.
If a carbon-based backfill with very high conductive property is used around the grounding electrode, it not only offers a very low resistance thereby keeping the current density low but also the moisture level becomes even less critical because within the carbon backfill, the conduction is electronic through the carbon particles, not through the moisture. Hence the current density around the electrode will remain low irrespective of the moisture content thereby helping maintain relatively a low resistance.
7) Will the compound shrink?
The volume of the carbon in LORESCO® PowerFill™ does not change as moisture or water level changes since carbon does not dissolve or react with water. As one of the inhibitors in the PowerFill™ contacts water, it dissolves in the water. Any void left by the dissolving inhibitor is quickly filled by the carbon particles settling into a more compact arrangement. Therefore, there is no shrinkage.
8) Do International Standards recommend carbon fills?
The BS 7430, The IEEE 80 and other major international standards recommend the use of special backfills to lower the electrode resistance as also to have a permanent solution where soil resistivity is an issue.
9) Why only the Carbon based grounding system is termed as maintenance free grounding?
The conventional system or Bentonite based system depend on Moisture to offer low resistance.
Whereas, this carbon based backfill system is not dependent on moisture and remains stable throughout its life and hence can be termed as truly – Maintenance free grounding.
10) What is more important to get a low resistance – Electrode or backfill?
The resistance can be lowered only by altering the medium adjacent to the electrode. The IEEE80, IS3043 and BS 7430 have all mentioned as under:
“To obtain overall low resistance, current density should be as low as possible for the MEDIUM ADJACENT TO THE ELECTRODE which should be so designed to cause the density to decrease rapidly with distance from the electrode.” The IEEE80 has also mentioned that the soil around the electrode should be modified to obtain a low earth resistance.
Thus the most important factor for obtaining low resistance value is SOIL TREATMENT i.e. the material around the electrode — which is the backfill material and not the electrode itself.
11) Can we get a low resistance by using a Copper Plate / Pipe Electrode?
The type of metal used has no significance on the earth electrode resistance. None of the formulae given in any of the international standards factor in the type of metal in calculation of the earth resistance.
However, it is to be noted that the copper electrode has a higher current handling capability as compared to the GI / steel electrode.
Also in highly corrosive areas, use of GI / Steel electrode may not be appropriate. Copper or copper coated electrodes have a better resistance to corrosion and hence are better suited in such areas.
12) Will use of bentonite give a maintenance free Earthing? If not what is the limitation of bentonite?
While Bentonite clay is effective in certain areas, it cannot be of help in all / dry areas. As per the IEEE 80 “Bentonite has a resistivity of 2.5 Ohm Mtr at 300% moisture. It may not function well in a dry environment because it may shrink away from the electrode increasing the electrode resistance.
13) Can any Earthing give resistance of < 1Ω with one electrode?
It is impossible to get the resistance of < 1Ω with individual electrodes in all areas. All standards of repute including IS, BS, IEEE80 etc categorically state, the resistance of the electrode depends on soil resistivity.
14) What are the possible solutions for rocky areas?
We can offer a variety of solutions for rocky areas like counterpoise earthing, radial earthing, Mat earthing, Satellite earthing , deep bore earthing etc. Depending on the site conditions and the requirements / applications, the right solution can be adopted. Our team will be happy to help you in suggesting a right method once all the required inputs are shared with us.
15) Can the UPS earth is clubbed with general earth?
In some UPS systems which have an isolation transformer, a separate neutral is derived on the output side through a dedicated earth pit. No other connections shall be made to this earth pit apart from UPS neutral. However, this earth pit shall be connected to the general earth grid underground to achieve equi-potential.
Technical Write ups
CARBON BASED BACKFILLS AND CURRENT FLOW ANALYSIS
LORESCO grounding enhancement formulations, Power Fill and PowerSet, are based primarily on carbon. Carbon is very stable when placed in the earth. Carbon has been used to surround electrodes discharging DC currents in the earth since the 1940’s due to its’ very stable nature. Even when discharging DC current the consumption rate of carbon is 2 lbs/ amp-year. Without a DC current discharge, carbon will last indefinitely since it is insoluble. As a comparison, copper consumes at a rate of 45 lbs / amp-year when discharging DC currents.
Although the carbon will not dissipate with time unless DC current is discharged, the resisitance-to-earth of an electrode surrounded with carbon-based grounding enhancement backfill can fluctuate over time due the changes in soil moisture. The carbon-based backfill is electronically conductive and does not rely on moisture for conduction. However, the earth is made up of primarily non-conductive minerals that cannot conduct current without moisture present in the soil. One of the major advantages of surrounding an electrode with PowerFill OR PowerSet backfill is the significant increase in contact surface area at the soil interface. This large surface area greatly reduces the dependence of the ground on soil moisture since the current density at the carbon/earth interface is much less than at the electrode interface. Therefore, soil moisture variations have much less effect on the resistance-to – earth of the electrode.
There are two conduction modes for current flow: electronic and electrolytic. Electronic conduction occurs as a result of movement of electrons within a metallic-type conductor. All electrodes conduct current electronic internally. Carbon, a metallic-type conductor, also conducts current electronically.
Hence carbon based backfills do not depend on moisture to conduct the current. The other conduction mode, electrolytic, usually occurs in liquids and involves movement of ions, not electrons. The earth is made of mostly non-conductive mineral grains with moisture within the pores of the grains or on the surface of the grains. Current conduction in the earth occurs through the moisture. This current flow is ionic (electrolytic) in nature involving both positive and negative ions dissolved in the moisture. Water, soil, clay or conductive liquids cannot conduct current electronically, hence the normal chemical grounding where backfill are primarily bentonite based, require moisture to conduct current.
When current is conducted ionically, mass movement occurs since ions are atoms with one or more electrons stripped away. This is why any chemical (ionic) treatment has a limited life because the ions released must move with the current flow. Electronic current movement does not involve mass movement since electrons are massless particles.
Thus, it is highly recommended to go in for this type of advanced grounding system which conforms to International standards. Product catalogue gives further details about the salient features of this product.
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