Siemens SIMOTICS XP 1LA5 - Page 29

Installation
Explosion-protected machines
56100000002002, 01/2016
101
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 5-1 Stator winding insulation resistance at 40° C
V
N
[V]
V
Meas
[V]
R
C
[MΩ]
U ≤ 1000
500
≥ 5
1000 ≤ U ≤ 2500
500 (max. 1000)
100
2500 < U ≤ 5000
1000 (max. 2500)
5000 < U ≤ 12000
2500 (max. 5000)
U > 12000
5000 (max. 10000)
U
rated
= rated voltage, see the rating plate
U
meas
= DC measuring voltage
R
C
= minimum insulation resistance at reference temperature of 40° C
Conversion to the reference temperature
When measuring with winding temperatures other than 40° C, convert the measuring
value to the reference temperature of 40° C according to the following equations from
IEEE 43-2000.
(1)
R
C
= K
T
· R
T
R
C
Insulation resistance converted to 40° C reference tem-
perature
k
T
Temperature coefficient according to equation (2)
R
T
Measured insulation resistance for measuring/winding
temperature T in °C
(2)
K
T
= (0.5)
(40-T)/10
40
Reference temperature in °C
10
Halving/doubling of the insulation resistance with 10 K
T
Measuring/winding temperature in °C
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.