Operation Manual

40 GMC-I Messtechnik GmbH
4.3 Polarization Index Measurement
A polarization index test is recommended for electrical machines.
This procedure involves expanded testing of insulation resistance.
DC measuring voltage from the MERISO PRIME+ is applied to
the insulation for a duration of 10 minutes. Measured values are
documented after one minute, and after ten minutes. If the insula-
tion is good, the value measured after ten minutes is higher than
the value measured after one minute. The relationship between
the two measurement values is the polarization index. Charged
material within the insulation is aligned due to the application of
measuring voltage over a long period of time, resulting in polariza-
tion. The polarization index indicates whether or not the charged
material contained in the insulation can still be moved, thus allow-
ing for polarization. This, in turn, is an indication of the condition of
the insulation.
The following rules apply in general:
PI values < 1 Troubleshooting is required.
PI values = 1 … 2 Maintenance is recommended.
PI values = 2 … 4 DUT is OK, no immediate action is
required. Preventive maintenance can be
planned according to the number of tests to
be performed.
PI values > 4 DUT is in flawless condition.
Applications
Determination of moisture and contamination levels
Absorption Index (DAR)
– DC Charging Test
The absorption index test is part of the polarization index test.
Insulation resistance measurements are placed in relationship to
one another after 30 and 60 seconds.
Application: Faster version of the polarization index text
TEST
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