- 13 -
The Polarization Index (PI) and Absorption Ratio (DAR) are tests to check
whether the leakage current of the insulator has increased. The leak current
did not increase while confirming the application time. The instrument
automatically calculates the polarization index PI and the absorption ratio
DAR. As a judgement of the insulation performance, both the polarization index
PI and the absorption ratio DAR indicate the change in the insulation
resistance over a period of time after the measured object withstands the
measured voltage.
7.2The difference between Polarization index
（
PI
）
and Absorption
ratio(DAR)
：
For general insulation tests, such as housing insulation, tool handles,
etc. can generally be tested in a relatively short period of time to increase
the leakage current with the increase of the voltage application time, so
generally can be tested with a short time test,the short-term insulation
resistance ratio DAR is called the absorption ratio (see the following formula
for the specific test time), but for the large-capacity and long-term
absorption process, such as transformers, generators, cables, capacitors and
other electrical equipment, sometimes the absorption ratio (DAR) is not
enough to reflect the whole process of absorption, and the insulation
resistance ratio can be used for a longer time, that is, the ratio between
the insulation resistance (R10min) at 10 minutes and the insulation
resistance (R1min) at 1 minute describes the entire process of insulation
absorption, and PI is called the polarization index.
The PI and DAR values are calculated by the following formula:
Remark
：
1
：
R10Min= resistance value measured by the voltage applied for 10 minutes
2
：
R1Min=R60Sec=the resistance value measured by the voltage applied for 1 minutes
3
：
R30Sec=It is the resistance value measured by the voltage applied for 30 seconds
4
：
R15Sec=It is the resistance value measured by the voltage applied for 15 seconds
5
：
DAR calculation time can choose 15 seconds or 30 seconds
PI(Polarization Index)=
Min
R
Min
R
1
10
DAR
（
Absorption ratio
）
=
Sec
R
Sec
R
15
60
DAR
（
Absorption ratio
）
=
Sec
R
Sec
R
30
60
