Siemens SIMOTICS 1LA, Compact Operating Instructions

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16BCommissioning
Standard motors
52
56100000002001, 02/2013
Note
If the measured value is close to the critical value, you must check the insulation
resistance at suitably frequent intervals.
Measuring the insulation resistance
1.
Before you begin measuring the insulation resistance, please read the operating
manual for the insulation resistance meter you are going to use.
2. Disconnect any main circuit cables from the terminals before measuring the
insulation resistance.
3. Where possible, measure the insulation resistance of the winding with respect to
the motor enclosure when the winding temperature is between 20 ... 30 °C.
Different insulation resistance values apply for other temperatures.
4. When measuring, wait until the final resistance value is reached. This is reached
after approximately one minute. Then read off the insulation resistance.
Limit values of the stator winding insulation resistance
The following table indicates the measuring circuit voltage and the limit values for the
minimum insulation resistance and the critical insulation resistance of the stator
winding.
Table 7-1 Insulation resistance of the stator unwinding at 25 °C
Rated voltage U
rated
< 2 kV
Measuring circuit voltage 500 V
Minimum insulation resistance for new, cleaned
or repaired windings
10 MΩ
Critical specific insulation resistance after a
long operating time
0,5 MΩ / kV
Note the following:
●
If the measurements are performed at winding temperatures ≠ 25 °C, convert the
measured value to the reference temperature of 25 °C in order to be able to
compare the values with the table above.
–
The insulation resistance halves every time the temperature rises by 10 K.
–
The resistance doubles every time the temperature falls by 10 K.
● Dry, new windings have a typical insulation resistance of more than
100 ... 2000 MΩ depending on the winding size, design and rated voltage. An