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Limit values for the winding insulation resistance
The following table specifies the measuring voltage and limit values for the insulation
resistance. These values correspond to the recommendations of IEC 60034-27-4 and
IEEE 43-2000.
Table 5- 1
U
rated
U
meas
R
= minimum insulation resistance at a reference temperature of 40 °C
C
Conversion to the reference temperature
When measuring at winding temperatures other than 40 °C, convert the measured value to
the reference temperature of 40 °C according to the following equations from IEC 60034-27-
4 and IEEE 43-2000.
In this case, doubling or halving the insulation resistance at a temperature change of 10 K is
used as the basis.
● The insulation resistance halves every time the temperature rises by 10 K.
● The resistance doubles every time the temperature falls by 10 K.
For a winding temperature of approx. 25° C, the minimum insulation resistances are 20 MΩ
(U ≤ 1000 V) or 300 MΩ (U > 1000 V). The values apply for the complete winding to ground.
Twice the minimum values apply to the measurement of individual assemblies.
● Dry, new windings have an insulation resistance of between 100 ... 2000 MΩ, or possibly
even higher values. An insulation resistance value close to the minimum value could be
due to moisture and/or dirt accumulation. The size of the winding, the rated voltage and
other characteristics affect the insulation resistance and may need to be taken into
account when determining measures.
● Over its operating lifetime, the motor winding insulation resistance can drop due to
ambient and operational influences. Calculate the critical insulation resistance value
1MB..1/2/3/4 - shaft heights 63 ... 355
Operating Instructions, 06/2020, A5E44455710A
Insulation resistance of the winding at 40 °C
U
N
V
U ≤ 1000
1000 ≤ U ≤ 2500
2500 < U ≤ 5000
5000 < U ≤ 12000
U > 12000
= rated voltage, see the rating plate
= DC measuring voltage
R
C
R
K
R
=
·
K
C
T
T
T
R
T
40
10
K
= (0.5)
T
(40-T)/10
T
500 (max. 1000)
1000 (max. 2500)
2500 (max. 5000)
5000 (max. 10000)
Insulation resistance converted to 40° C reference temperature
Temperature coefficient, see below
Measured insulation resistance for measuring/winding temperature
T
in °C
Reference temperature in °C
Halving/doubling of the insulation resistance with 10 K
Measuring/winding temperature in °C
5.2 Preparing for installation
U
meas
V
500
Assembly
R
C
MΩ
≥ 5
100
57
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