MI 3110 EurotestIM
Measurements
– a.c. LV IT installations
27
5.2.1 Line impedance and prospective short circuit current
Circuits for measurement of line impedance
Figure 5.7: Single phase IT line impedance measurement
– connection of 3-wire test
lead
Line impedance measurement procedure
❑
Select the
Zline
sub-function.
❑
Select test
parameters
(optional).
❑
Connect
test cable to the instrument.
❑
Connect
test leads to the item to be tested (see
❑
Press the
TEST
key to perform the measurement.
❑
Store
the result by pressing the MEM key (optional).
Figure 5.8: Example of line impedance measurement result
Displayed results:
Z .............. Line impedance,
I
SC
............ Prospective short-circuit current,
Lim .......... Low limit prospective short-circuit current value.
Prospective short circuit current is calculated as follows:
Z
k
Un
I
SC
SC
=
where:
Un ........ Nominal L1-L2 voltage (see table below),
ksc ....... Correction factor for Isc (see chapter 4.4.4).
U
n
Input voltage range (L1-L2)
110 V
(93 V
U
L-L
134 V)
230 V
(185 V
U
L-L
266 V)
