Siemens SIMOTICS XP - Checking the Insulation Resistance and Polarization Index of the Winding

Assembly
5.2 Preparations for installation
1MB..5/6 shaft height 71 ... 355
56 Operating Instructions, 07/2020, A5E41926185A
critical resistance value. Convert the value for the current winding temperature at the time
of measurement, see above table.
Measuring the polarization index
1. To determine the polarization index, measure the insulation resistances after one minute
and ten minutes.
2. Express the measured values as a ratio:
Polarization index = R
insul 10 min / Rinsul 1 min
Many measuring devices display these values automatically following the measurement.
Measuring the polarization index is not helpful for insulation resistances > 5000 MΩ, and is
therefore not included in the assessment.
R(10 min) / R(1 min)
Assessment
≥ 2
Insulation in good condition
< 2
Dependent on the complete diagnosis of the insulation
NOTICE
Damage to insulation
If the critical insulation resistance is reached or undershot, this can damage the insulation
and cause voltage flashovers.
• Contact the service center (Page 141).
• If the measured value is close to the critical value, you must subsequently check the
insulation resistance at shorter intervals.
See also
Insulation resistance and polarization index (Page 53)
Limit values of the anti-condensation heating insulation resistance
It is not permissible that the insulation resistance of the anti-condensation heating with
respect to the machine enclosure falls below 1 MΩ when measured at 500 V DC.