Siemens SIMOTICS XP 1MB155, Operating Instructions Manual

Page: 55 / 152

Assembly
5.1 Preparations for installation
1MB155 / 1MB555
Operating Instructions, 03/2018, A5E41926185A
53
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:
PI =
R
insul 10 min
/
R
insul 1 min
Many measuring devices display these values automatically following the measurement.
For insulation resistances > 5000 MΩ, the measurement of the PI is no longer meaningful
and consequently 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 50)
Limit values of the anti-condensation heating insulation resistance
The insulation resistance of the anti-condensation heating with respect to the machine
housing should not be lower than 1 MΩ when measured at 500 V DC.