JEF TECHNO SOLUTIONS PRIVATE LTD WELCOMES YOU FOR A TECHNICAL PRESENTATION ON MAINTENANCE FREE EARTHING
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Objective of Earthing A good earthing system is required for: Safety of human and animal life by limiting step and touch potential. To provide a sufficiently low impedance path to facilitate satisfactory protection operation under fault conditions in supply network to ensure good power Protection of buildings and installation against Lightning. Limitation of EMC i.e. limitation of electromagnetic disturbances
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How to achieve the above objectives
The above objectives are met by, Equipment Earthing System Earthing Fuctional earthing Lightning & static earthing :
Each one of these considerations places constraints on the design : - lightning and personnel safety dictate the design of earth Electrode. -Safety and installation protection dictate the size for the earthing conductors - the EMC behavior requirements determine the layout of earthing net work
CHALLENGES • • • •
Rocky areas Coastal Areas Difficulty in Maintenance Space restriction (GIS )
MEASURED EARTH RESISTANCE
EFFECT OF ELECTRODE ON EARTH RESISTANCE – R1 Resistance of Electrode • Effect on overall resistance – limited. • Hence, no significant difference in earth resistance between use of copper and steel electrodes. • Cannot reduce by having 2 separate electrodes – One inside another (like pipe in pipe, etc, .
FACTOR WHICH AFFECTS EARTH RESISTANCE – R3 • A Highly conductive backfill reduces current density and thus helps obtain a low earth resistance. • Hence the backfill compound is most important to reduce earth resistance.
RESISTANCE OF EARTH MASS (SOIL RESISTIVITY)– R5 • Varies according to soil condition at site
• Cannot be compensated entirely by any method / technology. • Effect can be minimised by using a highly conductive backfill for a small area around the electrode.
ELECTRODE GEOMETRY
RESISTANCE OF EARTH MASS (SOIL RESISTIVITY)– R5 Resistance of earth-effective artificial treatment area – IEEE -142 • Resistance of soil is sum of series resistance of virtual shells of earth. • Resistance decreases progressively outward from electrode. • Shell near to the electrode offers highest resistance due to smallest circumferential area. • 46% of the resistance occurs within 90 mm from electrode. • Hence artificial treatment of this first few inches of soil from electrode is most useful in improving effectiveness of earthing system.
ELECTRODE GEOMETRY – TABLE 9,IEEE 142 The resistance geometry of a ground electrode (pipe /rod) is explained as below : Around a grounding electrode the resistance of the soil is the sum of the series Resistances of virtual shells of earth located progressively outward from the rod. The shell nearest the rod has the smallest circumferential area or cross section. So it has the highest resistance. Successive shells outside this one have progressively Larger area and thus lower rÊsistance. As the radius from the rod increases the Incremental resistance per unit of radius decreases effectively to nearly zero. Experiments with a 10 ft,16 mm rod shows the following reading: Distance from electrode surface Ft 0.1 0.2 0.3 0.5 1.0 5.0 10.0 15.0 20.0 25.0
mtr 0.03 0.06 0.09 0.15 0.3 1.5 3.0 4.6 6.1 7.6
Approx. % of total resistance
25 38 46 52 68 86 94 97 99 100
Why Maintenance free earthing system
Electrodes are not just Fit and Forget items. To maintain its’ performance as designed originally, the electrodes needs periodical checking for its resistance value, watering to increase moisture content and replacement due to corrosion over periods.
Why Maintenance free earthing system
Practical difficulties in maintenance: • Electrode connection cannot be simply removed for measuring. Dangerous potential may arise. Hence plant needs shut down. • Replacement is still difficult job in energized substation. Also high cost involvement. • Watering if properly done incur significant running cost.Availablity of water is an issue.
Why Maintenance free earthing system
• The volume of soil influenced by an electrode of 10 ft rod will be 2095 cubic ft.57 cubic meter and approximate weight of soil will be 84960 Kgs. Minimum 5% moisture that can be expected at all seasons needs 4248 ltr per earth pit.
EARTHING STANDARDS
What do the Standards have to say on obtaining a low earth resistance?
A BRIEF OVERVIEW OF THE RECOMMENDATIONS OF VARIOUS INTERNATIONAL STANDARDS Parameters How to obtain a low overall Earth resistance?
IS-3043 To obtain a low overall resistance, the current density should be as low as possible in the medium adjacent to the electrode (Clause 9.1.1 page 19 of IS3043)
BS-7430 To obtain a low overall resistance, the current density should be as low as possible in the medium adjacent to the electrode Clause 9.5.1 Page 37 of BS 7430 2011.
IEEE80
REMARKS
It is impossible to achieve This clearly means that the desired reduction in a lower earth resistance the ground resistance by can be obtained by adding more grid conductors or ground rods. using a good and highly conductive backfill An alternate solution is to compound around the effectively increase the primary electrode and dia metre of the electrode not by using one by modifying the soil electrode inside another surrounding the or any such other electrode. The Inner shell special combination. of the soil closest to the The means of reducing electrode normally earth resistance is comprises the bulk of the backfill compound and electrode ground not a special electrode. resistance to remote earth (Clause 14.5 page 68 of IEEE 80
CONFORMITY TO STANDARDS
A BRIEF COMPARISON OF EARTHING SYSTEMS RECOMMENDED BY VARIOUS INTERNATIONAL STANDARDS Parameter
How to obtain a maintenance free Earth System?
IS-3043
BS-7430
IEEE80
If a great degree of In high resistivity locations Ground enhancement materials some with a permanence is or on rocky soil where envisaged, earth long term performance is resistivity of less than 0.1 Ohm meter (about electrodes required, it may be 5% resistivity of considered necessary to packaged in materials such as use conductive concrete Bentonite) are typically to improve earth contact placed around the rod Bentonite are in a augured hole in resistance around an preferable. (Clause either a dry or pre8.5 of Page 17 -- earth rod or strip. (Clause mixed in slurry. Some of THIS STANDARD 9.2.2. Page 34 BS7430these enhancement 2011) IS CURRENTLY materials are UNDER permanent and will not REVISION) leech in chemicals into the ground (Clause 14.5 of Page 68)
REMARKS All important international standards have recommended the use of special carbon based backfills to have a reliable and maintenance free earthing solution. The JEF Eco Safe Earthing solutions brought in by us is a Carbon based product and meets all parameters laid down by the IS, BS & IEEE & is truely maintenance free..
14.5 Soil Treatment to lower soil resistivity
IEEE Std 80: 2000
SOIL TREATMENT • • • • •
BS 7430 recommends conductive concrete. They shall not shrink away from electrode Consideration for non polluting charecteristics Chemicals not recommended Coke breeze not to be used.
DESIRED CHARECTERISTICS OF BACKFILL COMPOUND Resistance of backfilled area must remain consistently low to ensure a reliably low earth resistance. • Must not be subject to variation due to change in moisture / electrolyte content. • Backfill must not leach into ground.
• Backfill must not corrode the electrode
CONVENTIONAL EARTHING – CURRENT SCENARIO • No Standardisation - Neither in electrode nor in backfill. • Commercial grade GI pipe is used as electrode in most cases. • The backfill (Salt) reacts with the electrode (GI / Copper) and causes corrosion. • The salt dissolves in water and conductivity dips over time. • Not suitable for places with high water table, flowing water, etc,.
JEF ECO SAFE EARTHING – ADVANTAGES OF CARBON BACKFILL • Highly conductive – resistivity of < 0.1ohm mtr. • Conducts through flow of electrons like metal – eliminates the need for moisture. • Contains corrosion inhibitor to protect copper coating and doest not leach into ground. • Complies with the requirements of IEEE 80 and BS : 7430 for artificial treatment .
JEF ECO SAFE EARTHING ADVANTAGES • DOES NOT diffuse / leach into ground • Carbon is highly stable over long duration- does not degrade • Truly Maintenance Free
• Does not pollute environment - Certified by ANSI / NSF Standard 60 – Safe for use near potable ground water sources. • POWER SET which has hardening characteristics of cement can be used in areas with high water table.
CONDUCTION IN BENTONITE BACKFILLS - CONVENTIONAL
CONDUCTION IN CARBON BASED BACKFILLS
TERMINAL ARRANGEMENTS
BS 7430:2008
POSSIBLE SOLUTIONS FOR ROCKY AREAS
RADIAL EARTHING
MAT EARTHING
EQUIPOTENTIAL EARTHING
EQUIPOTENTIAL EARTHING
• LIGHTNING IMP CURRENT -100KA • RESPONSE VOLTAGE -- ≤ 10KA
• PROTECTION LEVEL -- ≤ 5KA • CONNECTOR – COPPER LUGS
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