Operation Manual

TeraOhm 5kV
21
Some applicable values:
DAR value Tested material status
< 1.25 Not acceptable
< 1.6 Considered as good insulation
> 1.6 Excellent
Note: When determining Riso (15s) pay attention to the capacitance of tested object. It
has to be charged-up in the first time section (15s). Approximate maximum capacitance
using:
[]
[
]
[]
V
s
F
U
t
C
.
.
3
10
3
max
= μ
,
where:
t........... period of first time unit (e.g. 15s)
U......... test voltage.
To avoid this problem increase
DIAG. Starting time parameter in CONFIGURATION
menu, because start of timer in DIAGNOSTIC TEST functions depends on output test
voltage. Timer begins to run when output test voltage reaches threshold voltage, which
is product of parameters
DIAG. Starting time and Unominal (nominal test voltage).
Using filters (fil1,fil2,fil3) in DAR function is not recommended!
Analyzing trend of measured insulation resistance and calculation of DAR and PI are
very useful maintenance tests of insulating material.
POLARIZATION INDEX (PI)
PI is the ratio of Insulation Resistance values measured after 1 minute and after 10
minutes. The DC test voltage is present during the whole period of the measurement
(also Insulation Resistance measurement is running). On completion of the test the PI
ratio is displayed:
(
)
()
min1
min10
R
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
.
.
3
10
3
max
= μ
,
where:
t........... period of first time unit (e.g. 1min)
U......... test voltage.
To avoid this problem increase
DIAG. Starting time parameter in CONFIGURATION
menu, because start of timer in DIAGNOSTIC TEST functions depends on output test