"Myths" and Mis (Concepts) On Earthing in Electrical System: by P.K.Pattanaik Optcl-Odisha
"Myths" and Mis (Concepts) On Earthing in Electrical System: by P.K.Pattanaik Optcl-Odisha
"Myths" and Mis (Concepts) On Earthing in Electrical System: by P.K.Pattanaik Optcl-Odisha
By
P.K.Pattanaik
OPTCL-ODISHA
1
MYTH: Story that embodies a BELIEF regarding some
FACT or Phenomenon of EXPERIENCE.
2
MIS-CONCEPT: GROUNDING and ERATHING both
are same in ELECTRICAL SYSTEM
Sl Grounding Earthing
1. Connection of Electrical System as Connection of Non-electrical
the FOURTH WIRE for 3 Phase conducting system as STRAIT
network has predominant role during PASS during charging condition.
fault condition
2. Safety to Electrical System from Safety to Working personnel to
abnormal condition of electrical avoid the unwanted current flow
parameter change through them
3. End termination for safety of the End termination for safety of
equipment. Human life and Live stocks
4 Design depends as per the action of Specific design of direct Earth
fault current calculation , Lead to the MOTHER EARTH mat
compromising the use of impedance for quick discharge of fault
on its path for limitation. current.
MIS-CONCEPT: EARTH is a POOR Conductor
Earth constituents mainly sand (silicon dioxide) with
other metallic oxides and surface layer of Clay mixed
sands and decayed matters.
Hence this can be treated as ELECTROLYTIC natured
material.
Electrically earth could be considered as circuit
containing variable resistance and capacitance.
100 4L
R loge ohms
2L d
where ρ resistivity of soil in ohmmeter
L length of rod in cm
d dia of rod in cm
R resistance in ohms
The Earth resistance depends upon the resistivity of the soil with its
constituents and dimension of the electrodes used. So the material
that used for the electrode has no role.
MYTH : Very Long rod/ pipe electrode shall reduce the
resistance substantially.
In both the case resistance value decreases, but decrease becomes more
for the case of increase of length as compared to diameter.
Note: For double of Length, Resistance decreases by 40%, but for the
double of the diameter, the resistance decreases by 10 to 12 %.
100 4L
R loge ohms
2L d
where ρ resistivity of soil in ohmmeter
L length of rod in cm
d dia of rod in cm
R resistance in ohms
MISCONCEPT : Adding More electrodes decreases the
resistance of earth mat substantially.
This perception is not correct in all cases. Adding more numbers of
electrodes may not cause that decrease of ER of the earth mat.
Using Laurent & Niemann method, Rg is calculated as below
Rg
4r lT 4 A lT
100 100
4 81X 41 244
0.76891884 0.40983606
1.178
V (a)
Rod 3 Rod 2(c)
Rod 1 (p)
EARTH
Electrode
Being tested
62 feet
50
(b)
40
Principles of an
30 earth resistance test
20
10
62 % line
0
0 20 40 60 80 100
Distance (from Rod1 to Rod3), Feet
MISCONCEPT : Sub-Station Gantry Tower Earthing
should be isolated.
Sub-station gantry tower helps to cause easy flow of fault current from the
source, resulting quick action of protection scheme. Incase this point does
not have direct link, then GPR may cause in the system resulting damage
to the system.
MISCONCEPT : Better Earth resistance reduces fault
current
NO, Earth resistance comes in series path of the fault current and if
its value is being chosen low, then fault current shall be more and
cause quicker flow from the source. So the protection scheme
shall actuate for quick time of isolation in the system. conductor.
MISCONCEPT : Earthing of LA, CVT should be of
separate system and not connected to earth mat in the
system.
The inductance of the grounding conductor may
introduce a high impedance to lightening current. As a result, the
potential drop per unit length of grounding conductor may be
high which may cause flashover with adjacent earthed structure /
conductor.
be Earthed
by Grounding.
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