Grounding and techniques

 A conducting connection, whether intentional or
accidental, between an electrical circuit or
equipment and the earth, or to some conducting
body that serves in place of earth.
 Ground is a connection to Earth made either
intentionally or accidentally.
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NEED OF GROUNDING:
 To protect people and equipment
from dissipating stray energy from:
1. Electrical faults (fuses, breakers
etc.)
2. Lightning strikes
3. Radio Frequency
4. Static discharges

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Electrical installations which need grounding:
The frames, tanks and enclosures of electric
machines, transformers and apparatus, lightning
fittings and so on.
Operating mechanism of the switchgear.
Framework of the switchboards, control boards,
individual panel boards.
Structural steelwork of indoor & outdoor substations,
metal cable jointing boxes, metal sheaths of cables &
similar metal works .

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Losses due to improper grounding:
 Estimation of at least 15% of power quality
problems are related to grounding.
 Lightning strikes on equipment with poorly
maintained protection systems destroy
millions of dollars of equipment and lost
production every year.
 Electric shocks, vibrations & noise from
electronic devices due to improper wiring,
also leads to mankind loss also.

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Types of grounding systems:
Different methods are available but the choice
depends on local conditions and required function.
Thus, we can see basically four types:
1. Single stake
2. Ground rod group
3. Ground plate
4. Ground mesh

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1. Single stake:
The simplest form of grounding element is the
ground stake, this can take many forms with a
variety of lengths from a few feet to many feet
long made of materials such as brass,
galvanised or stainless steel, the size and
material as required locally
The simple ground rod can be used for lightning
protection on stand-alone structures such as
pole mounted transformers or radio towers, it
can also be used as a back up to a utility ground.

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2. Ground rod group:
 A slightly more complicated version of the rod
system is the ground rod group, this is typically
for lightning protection on larger structures or
protection around potential hotspots such as
substations.

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3. Ground plate:
Ground plates are used widely in telecoms
applciations. They are particularly good where the
deeper ground has high resistivity.
For areas where there is rock (or other poor
conducting material) fairly close to the surface
ground plates are preferred as they are more
effective

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4. Ground mesh:
 A ground mesh consists of network of bars connected
together, this system is often used at larger sites such
as electrical substations.
 At substation site an area of ground could be
reserved at the start of the life of the substation with a
ground mesh under the whole of the site. As the site
grows over a period of years new equipment can
easily be installed and grounded by the mesh.

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Measurements
and
Techniques

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Steps involved:
1. Before grounding one has to know the resistivity
strength of the land or soil of the place.
2. Grounding tests are performed to know the
influence of spheres of influences.
3. Selection for type of grounding needed at the
place.
4. Grounding tests to know the depth and wide range
grounding needed for the site based on type of
devices or equipments used as loads.

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Ground testing methods:
1. Resistivity method( Wenner method):
Used to determine which type of earthing is
to be used by knowing the resistance(RE)
E = 2  . a . RE
E ...... mean value of soil resistivity
(W.m)
RE ...... measured resistance (W)
a ...... probe distance (m)

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2. Fall of potential testing( Three or Four pole method):
 Most commonly used method of testing.
 Three or four pole method, this refers to the number of
connections made to the ground tester.
 The forth pole of the connection is made if the wire to
connect to the system under test is particularly long >> 4
meters. The additional wire cancels out an error due to the
extended length of wire used.

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3. Selective measurement method:
 The selective method is based on the Fall of Potential
test.
 A current clamp is used to isolate the test current injected
into the electrodes under test, the current will flow to
earth by any path.

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4. The stake less method:
 Eliminates the need for temporary ground stakes.
 This is useful in a wide range of situations.
Eg: Inside buildings
Airports
Urban locations
Chemical and industrial plant
 The temporary ground stakes are replaced by two
current clamps. The first clamp generates a voltage on
the ground condutor, the second clamp measures the
current flowing due to the generated voltage.

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5. Two pole method:
 Used where other methods are
not available.
 Uses nearby metal structures as
a temporary spike.
 Metal water pipes are typically
used
Drawbacks:
 The resistance of the metal pipe
should be significantly less than
the electrode under test.
 Metal pipes are being replaced
with plastic.
 Some metal pipes use plastic
couplings.

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SUMMARY:
 Following Proper grounding methods decreases the
electrical faults.
 Improper grounding, no grounding for a plant or
substation or house are to be avoided.
 Get known resistivity of the land suitable method of
grounding is to be employed.
 Proper grounding is the sign of effective working of
equipment.

Grounding and techniques

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