The table below
indicates some practical values guide
values for different soil resistivity.
In galvanic corrosion caused contact
between two metals, the corrosion rate
is proportional the galvanic tension
between the metals. However, this measurement
requires only one voltage probe and cur-
rent electrode (auxiliary earth connection).
The summary gives this method:
- Probes and electrodes are placed as
illustrated, 90° from the main direction of
the earth connection. order limit
reciprocal connection between individual
earth connections, deep-earth connections
shall installed distance apart 1.13
Parallel connection.
- Measurement earth connection car-
ried out with open earth conductor clamp. can deter-
mined direct measurement with an
Ammeter calculated, the transition
resistance between the two electrodes
is known, according formula:
lk Rö
Ug galvanic voltage
In some cases, can measured with
a resistance bridge the same type used
to measure the earthing resistance an
earth connection.
Examples applicable requirements:
the lightning protection standard states Cu-
line min mm², EBR prescribes min.
The two methods that follow are method
of accurate technical measurement and a
more practical, simplified method.
There also clear correlation between
the corrosion rate and ground resistance. This means that when using
Elpress deep-earthing systems with cop-
per line, the cost will lower than when
using, for example, conventional systems.
- The reliability the measurement result
depends the location the probe/
auxiliary electrode.
Resistivity Corrosion
p 100 μm/year
p 1-10 100-30 μm/year
p 10-100 30-4 μm/year
p 100 negligible
. These provide normally acceptable
measurement accuracy.5l
2 0.
Method 2
(acc. The prerequisite for all types of
corrosion electrolyte fluid that al-
lows the transport positive metal ions
from anode cathode.
at least from the earth connection.
The rate corrosion depends the
composition the soil.5a-0. Cu-line
35 mm² for earth connections overhead
line networks and min. EBR-standard U2:80)
This method normally has measurement
error more than 2%, but practically is
easier perform than Method 1.
In the discussion the advantage of
deep-earth connections compared sur-
face-earth connections, should men-
tioned here that the earthing resistance
of horizontal surface-earth connection
is twice that similar line length a
deep- earth connection, i.
The summary gives this method:
- The probe and auxiliary electrode are
placed straight line from the earth con-
nection measured illustrated.
earth connection probe 0. The
largest value used.
- Measurement the resulting transition
resistance multiple earth connection
systems carried out with the clamp closed
and with the measuring line connected on
the top the earth conductor clamp.
Resulting earthing resistance:
Rres Rm
where the mean the resistance
value the earth connection and a
reduction factor, the value which is
obtained from the following table.
- the ground layered, measurement
should carried out two directions. the anode,
metal atoms are dissolved the electro-
lyte, forming free positive ions oxida-
tion- and the cathode these ions are
neutralized and deposited the metal
surface reduction.60
3 0.
The earthing resistance the earth connec-
tion usually measured with the same type
of instrument used measure the resist-
ance the soil. parallel earth connections for 1. base metal has
higher negative potential than nobler
metal and therefore forms the anode a
corrosion process.40
5 0. the lightning protection standard
SS 4870110).e.
No. At
a certain distance, this field can neglected
(removed earth).25
10 0. Influencing fac-
tors are the the soil, temperature,
oxygen content, moisture content and re-
sistivity.11:9
11
Earthing resistance
Due the high resistance the soil (109 x
resistivity metal) current bleed the soil
a strong electrical field formed the earth
connection, which diminishes strength
with distance from the earth connection. The rate corrosion is
often expressed μm/year where μm
represents 1/1000 and denotes
the thickness the corroded away outer
metal layer for year.
The location probes and electrodes varies
between different measurement methods.6a
earth connection electrode a
a m
a m
Measuring earthing resistance the
earth connection Method 2.e.
What important practice terms of
the cable diameter what currents the
system dimensioned for and what rules
and requirements apply.
R0 l
Parallel connection
Parallel connection several earth sockets
is often necessary for practical reasons to
achieve sufficiently low value earthing
resistance during earthing. Note the distance table
below.
With the help the conductivity and
the maximum earthing resistance, which
is required by, among other things, the
high current regulations, possible to
estimate how much line may needed
according the formula:
l R
l length metres
p soil resistance ohmmeter
R earthing resistance ohms.
Corrosion
The service life earth connection
depends its resistance corrosion
(rust). These factors affect the corrosion
current lk, which directly proportional
to the rate corrosion. This method has measure-
ment error 2%. mm² for earth
connections ground cable networks.
Measuring earthing resistance the
earth connection Method 1
Method 1
(acc.
From economic aspects can pointed
out that the diameter the earth con-
nection has negligible role when cal-
culating the earthing resistance deep
earthing.
-The position the probe/electrode equal
when measuring both individual earth
connection earth connection system, i.5
times the depth the earth connection l
