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Commissioning
5.1 Checking the insulation resistance
Wherever possible, measure the minimum insulation resistance of the winding to the motor
housing at a winding temperature of +20 °C to +30 °C. Other values for the insulation
resistance apply for temperatures outside this range. When making the measurement, wait
until the final resistance value is reached, approx. 1 minute.
Measure the critical insulation resistance at the operating temperature of the winding.
Limit values
The following limit values are valid for the insulation resistance at a rated voltage of
U
< 2 kV and a winding temperature of +25 °C.
N
500 V
10 MΩ
0.5 MΩ/kV
Observe the following:
● When measuring at winding temperatures other than +25 °C, the measured value must
be converted to the reference temperature of +25 °C. The insulation resistance is halved
for every 10 K increase in temperature, and it is doubled for every 10 K decrease in
temperature.
● If the insulation resistance is close to or below the minimum value, the cause could be
humidity and dirt accumulation. The windings must then be dried.
● During operation, the insulation resistance of the windings can fall to the critical insulation
resistance due to ambient and operational influences. The critical insulation resistance for
a +25 °C winding temperature can be calculated, depending on the rated voltage, by
multiplying the rated voltage (kV) by the specific critical resistance value (0.5 MΩ/kV);
e.g. critical resistance for rated voltage (U
44
Measuring circuit voltage
Minimum insulation resistance with new, cleaned or repaired windings
Critical specific insulation resistance after a long operating time
) 690 V: 690 V x 0.5 MΩ/kV = 0.345 MΩ.
N
Operating Instructions, 02/2015, 70000004023775
BA 2320
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