METREL MI 3298, Instruction Manual With Exercises

Page: 62 / 232

Power Network Application Trainer
– Earthing / Grounding network impedance measurement
62
Notes:

AC test current I
e
is injected through the test probe H (55 Hz … 1.5 kHz),

Impedance of probe H should be as low as possible (to inject higher test current),

Voltage drop is measured between probe S and ES,

The selective currents I
f1-4
is measured through the earthing electrodes Z
sel1-4
(pylon foots) selected by the user,

The selected earth impedance Z
sel1-4
is determined from the voltage U
S-ES
and
selected current (external current clamp
– I
f1-4
) ratio.

When using only one, two or three flex clamps, always connect one clamp to F1
terminal (synchronization port).

Make sure that the arrow marked on the clamp coupling points toward the correct
orientation for correct phase measurement.

Make sure that the number of turns is correctly entered in the test parameters
window
2.3.2.8 Passive (Flex Clamps) Measurement
The passive measuring method use the “Inductive current” or grounding wire current I
gw
flowing in the earthing system to determine the selected earth resistances of individual
earthing points (pylon foot). This passive method is useful for checking the consistency
of the measurements obtained with the selective (Flex Clamps 1 - 4) measurement
method.
Figure 43-2: Passive (Flex Clamps) measurement
“Inductive current” - I
gw
is actually an inductive coupling current between wires L1 (i1),
L2 (i2), L3 (i3) and overhead grounding wire line. This current has the same frequency
as the currents in lines L1, L2 and L3 (usually power frequencies 50 Hz or 60 Hz).