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6-4 DAR/PI Measurement function
1. PI – Polarization index
This is to check a temporal increase of leakage currents flowing on
insulations and to confirm leakage currents aren’t increased as time
passes.
PI is usually determined by the insulation resistances measured 1
min and 10 min after a measurement is started. PI is dependent
on the shape of insulations and influenced by moisture absorption,
therefore, a check of PI is important to diagnosis the insulation of
cables.
Insulation resistance
(10 min after a start of test)
Insulation resistance
(1 min after a start of test)
PI =
PI
4 or more
4
−
2
2.0
−
1.0
1.0 or less
Criteria
Best
Good
Warning
Bad
2. DAR - Dielectric Absorption Ratio
DAR measurement is almost same to PI measurement in a sense
that they test the time course of insulation. The only difference is
that DAR measurement can get result faster than the other.
Insulation resistance
(1 min after a start of test)
Insulation resistance
(15 or 30 sec min after a start of test)
*1
DAR =
DAR
1.4 or more
1.25
−
1.0
1.0 or less
Criteria
Best
Good
Bad
Note1: DAR time is selectable: 15 or 30 sec.
How to select:
(1) Keep the DISP button pressed down and rotate the Range
switch to power on KEW3126. (DAR mark blinks on the LCD.)
(2) Press the DISP button to switch 15 sec and 30 sec displayed at
the lower left on the LCD. Select the desirable one.
