Commissioning
8.4 Test the insulation resistance
SIMOTICS M-1FE2 built-in motors
Hardware Installation Manual, 04/2020, A5E50074509B AA
171
8.4 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.
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 (
U
n
) of
U
n
< 2 kV.
Table 8- 1 Stator winding insulation resistance at 25 °C
Minimum insulation resistance for new, cleaned or repaired
windings
10 MΩ
Critical specific insulation resistance after a long operating
0.5 MΩ/kV
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 shorte
r 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).
Precondition
The motor has reached the prescribed winding temperature of 25 °C.
Procedure for determining the insulation resistance
Calculate the critical insulation resistance at a winding temperature of 25 °C
● Multiply the rated voltage
U
n
by the specific critical resistance value of 0.5 MΩ/kV.
– Example: Critical resistance for a rated voltage
U
n
= 0.4 kV:
0.4 kV x 0.5 MΩ/kV = 0.2 MΩ
● Measure the insulation resistance of the winding in relation to the machine enclosure.
When measuring, wait about a minute until the final resistance value is reached.
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