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 6-1
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.
1FU9
Operating Instructions, 10/2023, A5E46712792A
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)
(40-T)/10
T
T
U
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
6.3 Preparing for installation
meas
V
500
Assembly
R
C
MΩ
≥ 5
100
57