METREL MI 3290 - Page 87

MI 3290 Earth Analyser Tests and Measurements
87
where:
Z
tot
..................................... Total selected earth impedance
Z
sel1-4/1
................................ Selected Earth impedance
I
gw
...................................... Inductive current or grounding wire current
I
f1-4
..................................... Measured current with Flex clamp
U
S-E
.................................... Test voltage between S and E terminal
Note:
 “Inductive current” - I
gw
in the example is actually an inductive coupling current
between wires L1 (i
1
), L2 (i
2
), L3 (i
3
) and overhead grounding wire loop. The current
has the same frequency as the L1, L2 and L3 current (usually power frequencies 50
Hz or 60 Hz).
Ze1
L1
L2
L3
i1
i2
i3
overhead grounding wire
Igw
overhead grounding wire loop
Re1
nex tower
Ze2 Ze3
Ze3
Figure 11.37: Substitute circuit for Passive (Flex Clamps) measurement
Test can be started from the Passive (Flex Clamps) measurement window. Before carrying
out a test the following parameters (Number of turns F1 - F4, Distance and Limit (Ztot)) can
be edited.
Figure 11.38: Passive (Flex Clamps) measurement menu
Test parameters for Passive (Flex Clamps):
Number of turns F1
Set the number of turns for Flex 1 input terminal: [1, 2, 3, 4, 5, 6]
Number of turns F2
Set the number of turns for Flex 2 input terminal: [1, 2, 3, 4, 5, 6]
Number of turns F3
Set the number of turns for Flex 3 input terminal: [1, 2, 3, 4, 5, 6]
Number of turns F4
Set the number of turns for Flex 4 input terminal: [1, 2, 3, 4, 5, 6]
Distance (r)
Distance between E and S probe (user defined).
Limit (Ztot)
Limit value selection: [OFF, 0.1 Ω – 5.00 kΩ]
Passive (Flex Clamps) Measurement procedure:
 Select the Passive (Flex Clamps) measurement function.
 Set the test parameters (number of turns, distance and limit).
 Connect the test leads and flex clamps to the instrument and to the test object.
 Press the Run key to start the measurement.
 Wait until the test result is displayed on the screen.
 Press the Run key again to stop the measurement.
 Press the cursor keys to toggle between multiple result views (optional).
 Save results (optional).