The document discusses grounding systems and their objectives which are to provide safety, ensure correct operation of equipment, prevent damage, dissipate lightning, stabilize voltage, and divert stray RF energy. It describes the three main types of grounding as equipment, system, and lightning/surge grounding. Various grounding components and methods are defined including earth electrodes, earthing conductors, earthing grids, soil characteristics, recommended earth resistance values, and substation earthing systems. New methods to decrease ground resistance such as chemical rods, grounding augmentation fill, and cracks filled with low resistivity materials are also summarized.

1. GROUNDING SYSTEMS
Part 1

2. The objective of a grounding system are:
1. To provide safety to personnel during normal and fault
conditions by limiting step and touch potential.
2. To assure correct operation of electrical/electronic
devices.
3. To prevent damage to electrical/electronic apparatus.
4. To dissipate lightning strokes.
5. To stabilize voltage during transient conditions and to
minimize the probability of flashover during transients.
6. To divert stray RF energy from sensitive audio, video,
control, and computer equipment.

3. A safe grounding design has two objectives:
1. To provide means to carry electric currents
into the earth under normal and fault
conditions without exceeding any operating
and equipment limits or adversely affecting
continuity of service.
2. To assure that a person in the vicinity of
grounded facilities is not exposed to the
danger of critical electric shock.

4. The PRIMARY goal of the grounding
system throughout any facilities is
SAFETY.
Why ground at all?
PERSONNEL SAFETY FIRST
EQUIPMENT PROTECTION SECOND

5. The three main types are:
 EQUIPMENT GROUNDING (SAFETY)
 SYSTEM GROUNDING
 LIGHTNING/SURGE GROUNDING
What are the three main types
of grounding?

7. Soil Characteristics
 Soil type. Soil resistivity varies widely
depending on soil type, from as low as 1
Ohmmeter for moist loamy topsoil to almost
10,000 Ohm-meters for surface limestone.
 Moisture content is one of the controlling
factors in earth resistance because electrical
conduction in soil is essentially electrolytic.

9. DEFINITIONS
•EATRH
•Earth electrode
•Earth Electrode Resistance
•Earth fault current
•Earthing grid
•Earthing conductor
•Earthing system

10. Test link
Cable(Earthing conductor)
Clamp
Rod(Earthing electrode)
Rod coupler

11. Classification of low voltage systems
•TN system
•TT system
•IT system

12. TN systems
source
Consumer terminal load
TN-C
N&E
source
Consumer terminal load
TN-S
N
E

13. source
Consumer terminal load
N
E
TT system
source
Consumer terminal load
N
E
IT system
High impedance

14. Factors involved in effective earthing
•Effect of shape on electrode resistance
•Soil resistivity
•Plate
•Rod
•Horizontal strip or round conductor electrodes

15. Recommended values of earth resistance
Recommended earth
resistance(ohm)
system
0.5-1
Light current
5
Low voltage
2.5
Medium
voltage
0.5
High voltage

16. Substation earthing system
•Step & Touch voltage
•Grounding grids

17. Step and touch voltages

19. Step potential
 “Step potential” is the voltage
between the feet of a person standing
near an energized grounded object.
 It is equal to the difference in voltage,
given by the voltage distribution curve,
between two points at different
distances from the “electrode.”
 A person could be at risk of injury
during a fault simply by standing near
the grounding point.

20. Touch potential
 “Touch potential” is the voltage between
the energized object and the feet of a
person in contact with the object.
 It is equal to the difference in voltage
between the energized object and a point
some distance away.
 The touch potential could be nearly the
full voltage across the grounded object if
that object is grounded at a point remote
from the place where the person is in
contact with it.

21. Driven rods

22. Resistance of driven rods:
 The Ground Resistance (R) of a single rod, of diameter (d) an
driven length (i) driven vertically into the soil of resistivity (ρ), can
be calculated as follows:
where: ρ Soil Resistivity in m
l Buried Length of the electrode in m
d Diameter of the electrode in m
The rod is assumed as carrying current uniformly along its rod.
 Examples
(a) 20mm rod of 3m length and Soil resistivity 50 Ω-m .....R=16.1 Ω
(b) 25mm rod of 2m length and Soil resistivity 30 Ω-m .....R=13.0 Ω













 1
8
ln
2 d
l
l
R



23. Earth resistance shells surrounding a
vertical earth electrode

24.  The resistance of a single rod is not sufficiently
low.
 A number of rods are connected in parallel.
 They should be driven far apart as possible to
minimize the overlap among their areas of
influence.
 It is necessary to determine the net reduction in
the total resistance by connecting rods in
parallel.
 The rod is replaced by a hemispherical
electrode having the same resistance.

25. Rod Electrodes in Parallel
 If the desired ground resistance cannot be
achieved with one ground electrode, the overall
resistance can be reduced by connecting a
number of electrodes in parallel.
 These are called “arrays of rod electrodes”.
 The combined resistance is a function of the
number and configuration of electrodes, the
separation between them, their dimensions and
soil resistivity.
 Rods in parallel should be spaced at least twice
their length to utilize the full benefit of the
additional rods.

26.  If the separation of the electrodes is much
larger than their lengths and only a few
electrodes are in parallel, then the resultant
ground resistance can be calculated using the
ordinary equation for resistances in parallel.
 In practice, the effective ground resistance will
usually be higher than this.
 Typically, a 4 spike array may provide an
improvement of about 2.5 to 3 times.
 An 8 spike array will typically give an
improvement of may be 5 to 6 times.

27. The multiple driven rod electrode
 The driven rod is an economical and simple means
of making an earth connection but its resistance is
not sufficiently low.
 A number of rods are connected in parallel.
 They should be driven far apart as possible to
minimize the overlap among their areas of
influence.
 It is necessary to determine the net reduction in the
total resistance by connecting rods in parallel.
 The rod is replaced by a hemispherical electrode
having the same resistance.

28.  The method consists of assuming that
each equivalent hemisphere carries the
same charge.
 Calculate the average potential of the
group of rods.
 From this and the total charge the capacity
and the resistance can be calculated.

30. Two ground electrodes
Equivalent
hemisphere

31. Earth clamping 1
AT-090H AT-090H
Earth clamping 2
AT-087J AT-089J AT-093J

32. Conductors
Bare copper tape Tinned copper tape PVC covered copper tape
Aluminium tape PVC covered aluminium tape Stranded copper cable
Round cable PVC covered stranded copper cable PVC covered round cable

33. AT-010H AT-011K AT-012K
Bonding bars
AT-020H AT-051F AT-054J AT-050F

34. METHODS OF DECREASING GROUND
RESISTANCE
 Decreasing the ground resistance of a
grounding system in high resistivity soil is
often a formidable task.
 Recently, some new methods have been
proposed to decrease ground resistance.

35. 1-Chemical Rods
 Chemical rods are electrodes with holes along
their length, filled with mineral salts.
 The specially formulated mineral salts are
evenly distributed along the entire length of the
electrode.
 The rod absorbs moisture from both air and soil.
 Continuous conditioning of a large area insures
an ultra-low-resistance ground which is more
effective than a conventional electrode.

36.  If the conductive salts are running low, the
rod can be recharged with a refill kit.
 These rods are available in vertical and
horizontal configurations.
 They may be used in rocky soils, freezing
climates, dry deserts, or tropical rain
forests.
 They provide stable protection for many
years.

43. Disadvantages are:
 Chemicals concentrated around
electrodes will cause corrosion
 Chemicals leach through the soil and
dissipate
 Scheduled replacement may be required
 May be prohibited because they may
contaminate the water table

44. 2- Grounding Augmentation Fill (GAF)
 About 95% of the grounding resistance of a
given electrode is determined by the character
of the soil within a hemisphere whose radius is
1.1 times the length of the rod.
 It is obvious that replacing all or part of that soil
with a highly conductive backfill will facilitate the
achievement of a low-resistance ground
connection.
 The greater the percentage of soil replaced, the
lower the ultimate grounding resistance.

45. The critical soil cylinder within an
interfacing hemisphere

46.  The amount of the backfill material required is
determined in most cases by the Interfacing
Volume and Critical Cylinder principles.
 A ground electrode establishes a connection to
earth by affecting only a certain volume of
earth, called the Interfacing Volume (IV).
 For practical purposes for a ground rod the
entire connection to earth is contained within
an IV whose radius is 2.5 times the length of
the rod.

47.  Most of the earth connection takes place in a
cylinder close to the electrode, called the
Critical Cylinder.
 A study of the influence of soil within the IV
demonstrates that six inches of soil along any
radial makes up 52 per cent of the connection
to earth; a 12 inches makes up 68 percent of
the connection.

48.  Beyond a diameter of 24 inches there is
very little improvement for much larger
diameters.
 Therefore, the recommended diameter for
the Critical Cylinder is between 12 and 24
inches, and the calculated amount of the
required backfill material is based on that
diameter and the length of the ground rod.

49. 3- Cracks with Low Resistivity Materials
(LRM)
This method requires 3 steps:
 Drilling deep holes in the ground, developing
cracks in the soil by means of explosions in
the holes, filling the holes with low resistivity
materials (LRM) under pressure.
 Most of the cracks around the vertical
conductors will be filled with LRM, and a
complex network of low resistivity tree like
cracks linked to the substation grid is formed.

50.  Field tests show that the optimum span
between vertical conductors is in the range
of 1.5-2 times the length of the vertical
conductor.
 This method is effective in reducing
ground resistances in rocky areas.

52. Soil Treatment Alternatives
 Ground enhancement material
Cement-like compound
 Non-corrosive
 Extremely conductive
 Installed around the electrode
 Easy installation
 Permanent

53. Conductive Cement
Concrete has a resistivity range of 30 to 90 Ohm-
meters.
 Since it is hygroscopic by nature it will tend to absorb
moisture when available and keep it up to 30 days,
thus maintaining a resistivity lower than the
surrounding soil.
 However, during a long dry season concrete will dry
out with a subsequent rise in resistivity.
 Also, if a substantial amount of fault or lightning
current is injected into a concrete encased electrode,
the moisture in the concrete may become steam,
dramatically increasing in volume and placing a
substantial stress on the concrete.

54.  Installing an EARTHLINK 101 earthling strip is
simple:
Dig a trench and lay in the wire.

55. Pour EARTHLINK 101 conductive cement, using the handy
applicator bag, and shovel in a thin protective layer of soil.

56. Backfill the remaining soil using a front-end loader
and restore the surface to grade.