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4.1 Preparations
● When measuring, wait until the final resistance value is reached; this takes approximately
Stator winding insulation resistance limit values
The following table shows the measuring circuit voltage and the limit values for the minimum
insulation resistance and the critical insulation resistance for the stator winding.
Table 4-1
Measuring circuit voltage
Minimum insulation resistance with new, cleaned or
repaired windings
Critical specific insulation resistance after a long operating
time
Note the following:
● Dry, new windings have insulation resistance of between 100 and 2000 MΩ, or possibly
● Over its operating lifetime, the motor winding insulation resistance can drop due to
NOTICE
Critical insulation resistance is reached or insufficient
If the critical insulation resistance is reached or is insufficient, damage to the insulation and
flashover voltages can result.
Dry the windings or clean and dry them thoroughly, having first removed the rotor.
If the clean windings have not cooled to 25°C, then lower insulation resistance will be
measured. The insulation resistance can only be properly assessed after conversion to the
reference temperature of 25°C. Allow the windings to cool to 25°C or convert the insulation
resistance using 25°C as the reference temperature.
If the measured value is close to the critical value, you must check the insulation resistance
at appropriately frequent intervals subsequently.
[ID: 344.01]
44
one minute.
Stator winding insulation resistance at 25 °C
values that are even higher.
If the insulation resistance is close to the minimum value, then the cause could be
humidity and/or fouling.
ambient and operational influences. The critical insulation resistance at a winding
temperature of 25°C is 2.5 MΩ
Rated voltage U
< 2 kV
N
500 V (min. 100 V)
10 MΩ
2.5 MΩ/kV
Siemens AG Operating Instructions 2.02 1PL622
A5E00264365A
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