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12 THEORETICAL APPENDIX
12.1 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 (an
Insulation Resistance measurement is also running). On completion of the test the PI ratio
is displayed
General applicable values:
PI value
from 1.0 to 2.0
from 2.0 to 4.0
12.2 DIELECTRIC ABSORBTION RATIO (DAR)
DAR is ratio of insulation resistance values measured after 30s and after 1 minute. The
DC test voltage is present during the whole period of the test (also an Insulation
Resistance measurement is continually running). At the end, the DAR ratio is displayed:
General applicable values:
DAR value
from 1.0 to 1.25
from 1.25 to 1.6
< 1.0
> 4.0
< 1.0
> 1.6
Insulation conditions
Insulation conditions
EN - 32
HT7051 - HT7051N
Dangerous
Not acceptable
Good
Excellent
Dangerous
Not acceptable
Good
Excellent
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