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5. Read out the insulation resistance one minute after applying the measuring
voltage.
Limit values for the stator winding insulation resistance
The following table specifies the measuring voltage and limit values
for the insulation resistance. These values correspond to IEEE 43-2000
recommendations.
Table 3-1 Stator winding insulation resistance at 40 ºC
U
rated
U
meas
R
C
Conversion to the reference temperature
When measuring with winding temperatures other than 40 ºC, convert the
measuring value to the reference temperature of 40 ºC according to the
following equations from IEEE 43-2000.
K
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 ºC, the minimum insulation
resistances are 20 M Ω (U ≤ 1000 V) or 300 M Ω (U > 1000 V). The values
apply for the complete winding to ground. Twice the minimum values apply
to the measurement of individual assemblies.
84
U
V
N
U ≤ 1000
1000 ≤ U ≤ 2500
2500 < U ≤ 5000
5000 < U ≤ 12000
U > 12000
= rated voltage, see the rating plate
= DC measuring voltage
= minimum insulation resistance at a reference temperature of 40 ºC
R
C
(1)
K
T
R
= K
· R
C
T
T
R
T
40
(2)
10
= (0.5)
(40-T)/10
T
T
U
V
meas
500
500 （ max. 1000 ）
1000 （ max. 2500 ）
2500 （ max. 5000 ）
5000 （ max. 10000 ）
Insulation resistance converted to 40 ºC reference
temperature
Temperature coefficient according to equation (2)
Measured insulation resistance for measuring/winding
temperature T in ºC
Reference temperature in ºC
Halving/doubling of the insulation resistance with 10 K
Measuring/winding temperature in ºC
R
M Ω
C
≥ 5
100
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