MI 3201 TeraOhm 5 kV Plus Measurements
28
min1
min10
R
iso
iso
PI
Note: When determining Riso (1min) pay close attention to the capacitance of the object
under test. It has to be charged-up in the first time section (1 min). Approximate
maximum capacitance using:
V
s
F
U
t
C
10
3
max
.
where:
t........... period of first time unit (e.g. 1min)
U.........test voltage.
To avoid this problem, increase the DIAG. Starting time parameter in
CONFIGURATION menu, because the start of timer in the DIAGNOSTIC TEST
functions depends on the test voltage. The timer begins to run when test voltage
reaches the threshold voltage, which is product of the DIAG. Starting time and nominal
test voltage (Unominal).
Analysing the change in the measured insulation resistance over time and calculating
the DAR and PI are very useful maintenance tests of an insulating material.
DIELECTRIC DISCHARGE TESTING (DD)
DD is the diagnostic insulation test carried out after the completion of the Insulation
Resistance measurement. Typically the insulation material is left connected to the test
voltage for 10 30 min and then discharged before the DD test is carried out. After 1
minute a discharge current is measured to detect the charge re-absorption of the
insulation material. A high re-absorption current indicates contaminated insulation
(mainly based on moisture):
FCVU
mAIdis
DD
.
min1
,
here:
n ......discharging current measured 1 min after regular discharge
of test object.
w
Idis 1mi
U.................. test voltage
C.................. capacitance
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