MI 3110 EurotestIM
Measurements
– a.c. LV IT installations
34
When MANUAL I or AUTO I sub-function is selected, start value of insulation
resistance is determined by
it
L
L
start
I
U
R
lim
2
1
5
.
1
−
Figure 5.17: Examples of IMD test results
Displayed results:
R1 ........... threshold indicative insulation resistance for L1,
R2 ........... threshold indicative insulation resistance for L2,
I1 ............ calculated first fault leakage current for R1,
I2 ............ calculated first fault leakage current for R2.
Calculated first fault leakage current at threshold insulation resistance is given as:
)
2
(
1
2
1
)
2
(
1
R
U
I
L
L
−
=
U
L1-L2
is line-line voltage. The calculated first fault current is the maximum current that
would flow when insulation resistance decreases to the same value as the applied test
resistance, and a first fault is assumed between opposite line and PE.
