Application Note

H/C2
OFF
3
POLE
4
POLE
4
POLE
2
POLE
S/P2
ES/P1
E/C1
START
TEST
DISPLAY
MENU
CHANGE
ITEM
SELECT
1625-2
ADVANCED EARTH / GROUND TESTER GEO
E S H
AC
Rresistance
300kΩEarth/Ground Resistance 300kΩ
DC
Resistance 3kΩ
RA
R
—
R
~
2
POLE
3
POLE
3
POLE
4
POLE
EI-162X
SENSING CURRENT
TRANSFORMER
EI-162AC
INDUCING CURRENT
TRANSFORMER
>10 cm (4 in)
H/C2
OFF
3
POLE
4
POLE
4
POLE
2
POLE
S/P2
ES/P1
E/C1
START
TEST
DISPLAY
MENU
CHANGE
ITEM
SELECT
1625-2
ADVANCED EARTH / GROUND TESTER GEO
SES
AC
Rresistance
300kΩEarth/Ground Resistance 300kΩ
DC
Resistance 3kΩ
RA
R
—
R
~
2
POLE
3
POLE
3
POLE
4
POLE
ST
11
Two-pole ground resistance
In situations where the driving of ground stakes is neither
practical nor possible, the Fluke 1623-2 and 1625-2 tes-
ters give you the ability to do two-pole ground resistance/
continuity measurements, as shown below.
To perform this test, the technician must have access to a
good, known ground such as an all metal water pipe. The
water pipe should be extensive enough and be metallic
throughout without any insulating couplings or flanges.
Unlike many testers, the Fluke 1623-2 and 1625-2 per-
form the test with a relatively high current (short circuit
current > 250 mA) ensuring stable results.
Equivalent circuit for
two-point measurement.
Ground impedance measurements
When attempting to calculate possible short
circuit currents in power plants and other high
voltage/current situations, determining the com-
plex grounding impedance is important since
the impedance will be made up of inductive
and capacitive elements. Because inductivity
and resistivity are known in most cases, actual
impedance can be determined using a complex
computation.
Since impedance is frequency dependent,
the Fluke 1625-2 uses a 55 Hz signal for this
calculation to be as close to voltage operating
frequency as possible. This ensures that the
measurement is close to the value at the true
operating frequency. Using this feature of the
Fluke 1625-2, accurate direct measurement of
grounding impedance is possible.
Power utilities technicians, testing high voltage
transmission lines, are interested in two things:
the ground resistance in case of a lightning
strike, and the impedance of the entire system
in case of a short circuit on a specific point in the
line. Short circuit, in this case, means an active
wire breaks loose and touches the metal grid of
a tower.