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7.3
Test the insulation resistance
After long storage or shutdown periods, you must check the insulation resistance of the
windings with respect to ground using a DC voltage.
● Always measure the insulation resistance of the winding to the motor housing when the
winding temperature is between 20° and 30° C.
● When measuring, wait until the final resistance value is reached. This will take
approximately one minute.
Limit values
The table below specifies the measuring circuit voltage as well as the limit values for the
minimum insulation resistance and the critical insulation resistance with a rated motor
voltage of V
Table 7- 7
Measurement 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 an insulation resistance of between 100 and 2000 MΩ.
Note
Measured value of the insulation resistance near the critical value
If the measured value lies near the critical value, the insulation resistance must be
checked in shorter intervals.
Values apply to the measurement at a winding temperature of 25° C.
● The insulation resistance of the motor winding can reduce during the course of its service
life due to ambient and operational influences (moisture, contamination).
● Calculate the critical insulation resistance at a winding temperature of 25° C by
multiplying the rated voltage (kV) by the specific critical resistance value (0.5 MΩ/kV).
Example: critical resistance for the rated voltage (V
0.6 kV x 0.5 MΩ/kV = 0.3 MΩ
1FE1 synchronous built-in motors
Hardware Installation Manual, 12/2016, 610.43000.40b
< 2 kV:
N
Stator winding insulation resistance at 25° C
7.3 Test the insulation resistance
Rated voltage V
< 2 kV
N
500 V (minimum, 100 V)
10 MΩ
0.5 MΩ/kV
) = 0.6 kV:
N
Commissioning
125
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