CPC 100
V 3.20
Resistance - 3
Use the
RGround
test card to determine earth resistance between a substation’s ground
system and a remote auxiliary electrode. To measure the earth resistance, the
CPC 100
injects
AC current between the substation’s ground system and a temporary remote auxiliary electrode.
A second auxiliary electrode is used to measure the voltage potential across the substation’s
earth resistance.
Note:
Make sure not to position the auxiliary electrode U too close to the substation’s ground
system. If you do so, you measure in a range where the earth resistance may not be linear (see
figure below).
We suggest to test several points using a longer distance to the substation ground. That way
you get a better understanding of where the linear range of the earth resistance lies, and where
the measurements are reliable.
Theoretical resistance characteristic of an earth electrode:
Measuring the Ground Resistance of Small Ground Systems
Measuring the Ground Resistance of Large Ground Systems
linear range of earth resistance
Distance
100
200
300
400
500
600
0
Earth resistance in m
U
3...5 x a
10xa
Auxiliary
electrode U
Auxiliary
electrode I
90º
(Bird’s-eye view)
a
I
a
Substation ground
a= size of the earthing system
Auxiliary
electrode U
> 1km
U
3...5 x a
a
a
Substation A ground
Substation B ground
I
a= size of the earthing system
RGround
