JEF TECHNO SOLUTIONS PRIVATE LTD WELCOMES YOU FOR A TECHNICAL PRESENTATION ON MAINTENANCE FREE EARTHING
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JEF
JEF TECHNO SOLUTIONS PRIVATE LTD
WELCOMES YOU FOR A TECHNICAL PRESENTATION
ON MAINTENANCE FREE EARTHING
JEF ECOSAFE ELECTRICAL GROUNDING
Objective of Earthing
A good earthing system is required for:
1. Safety of human and animal life by limiting step and touch potential.
2. To provide a sufficiently low impedance path to facilitate satisfactory protection operation under fault conditions in supply network to ensure good power
3. Protection of buildings and installation against Lightning.
4. Limitation of EMC i.e. limitation of electromagnetic disturbances
. 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 résistance. 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 Approx. % of total resistance Ft mtr 0.1 0.03 25 0.2 0.06 38 0.3 0.09 46 0.5 0.15 52 1.0 0.3 68 5.0 1.5 86 10.0 3.0 94 15.0 4.6 97 20.0 6.1 99 25.0 7.6 100
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?
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 IS-
3043)
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
It is impossible to achieve
the desired reduction in
the ground resistance by
adding more grid
conductors or ground rods.
An alternate solution is to
effectively increase the
dia metre of the electrode
by modifying the soil
surrounding the
electrode. The Inner shell
of the soil closest to the
electrode normally
comprises the bulk of the
electrode ground
resistance to remote earth
(Clause 14.5 page 68 of
IEEE 80
REMARKS
This clearly means that
a lower earth resistance
can be obtained by
using a good and highly
conductive backfill
compound around the
primary electrode and
not by using one
electrode inside another
or any such other
special combination.
The means of reducing
earth resistance is
backfill compound and
not a special electrode.
A BRIEF OVERVIEW OF THE RECOMMENDATIONS OF VARIOUS INTERNATIONAL STANDARDS
IS-3043
If a great degree of
permanence is
envisaged, earth
electrodes
packaged in
materials such as
Bentonite are
preferable. (Clause
8.5 of Page 17 --
THIS STANDARD
IS CURRENTLY
UNDER
REVISION)
BS-7430
In high resistivity locations
or on rocky soil where
long term performance is
required, it may be
considered necessary to
use conductive concrete
to improve earth contact
resistance around an
earth rod or strip. (Clause
9.2.2. Page 34 BS7430-
2011)
IEEE80
Ground enhancement
materials some with a
resistivity of less than
0.1 Ohm meter (about
5% resistivity of
Bentonite) are typically
placed around the rod
in a augured hole in
either a dry or pre-
mixed in slurry. Some of
these enhancement
materials are
permanent and will not
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..
CONFORMITY TO STANDARDS
A BRIEF COMPARISON OF EARTHING SYSTEMS RECOMMENDED BY VARIOUS INTERNATIONAL STANDARDS
Parameter
How to obtain a maintenance free Earth System?
IEEE Std 80: 2000 14.5 Soil Treatment to lower soil resistivity
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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