Siemens SIMOTICS XP 1LA5 Compact Operating Instructions page 30

Installation
● Dry, new windings have an insulation resistance of between 100 and 2000 MΩ, or
possibly even higher values. An insulation resistance value close to the minimum
value could be due to moisture and/or dirt accumulation. The size of the winding,
the rated voltage and other characteristics affect the insulation resistance and
may need to be taken into account when determining measures.
● Over its operating lifetime, the motor winding insulation resistance can drop due
to ambient and operational influences. Calculate the critical insulation resistance
value depending on the rated voltage by multiplying the rated voltage (kV) by the
specific 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
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 / R
(10 min) (1 min)
≥ 2
< 2
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 145).
•
If the measured value is close to the critical value, you must subsequently check
•
the insulation resistance at shorter intervals.
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.
102
/ R
insul 1 min
Dependent on the complete diagnosis of the insulation
Assessment
Insulation in good condition
Explosion-protected machines
56100000002002, 01/2016