Lamb LABA-WDMO-0814 Betriebsanleitung Seite 23

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The insulation resistance must be measured with a megohmmeter. The machine must be in cold state and
disconnected from the power supply.
To prevent the risk of an electrical shock, ground the terminals before and after each measurement.
Ground the capacitor (if any) to ensure that it is fully discharged before the measurement is taken.
It is recommended to insulate and test each phase separately. This procedure allows the comparison of the
insulation resistance between each phase. During the test of one phase, the other phases must be grounded.
The test of all phases simultaneously evaluates the insulation resistance to ground only but does not evaluate
the insulation resistance between the phases.
The power supply cables, switches, capacitors and other external devices connected to the motor may
considerably influence the insulation resistance measurement. Thus all external devices must be disconnected
and grounded during the insulation resistance measurement.
Measure the insulation resistance one minute after the voltage has been applied to the winding. The applied
voltage should be as shown in Table 5.3.
Winding rated voltage (V)
< 1000
1000 - 2500
2501 - 5000
5001 - 12000
> 12000
The reading of the insulation resistance must be corrected to 40 °C as shown in the Table 5.4.
Table 5.4 - Correction factor for the insulation resistance corrected to 40 °C
Measuring temperature
of the insulation
resistance (°C)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
76 Manual of Electric Motors
Table 5.3 - Voltage for the insulation resistance
Correction factor of the
insulation resistance
corrected to 40 °C
0.125
0.134
0.144
0.154
0.165
0.177
0.189
0.203
0.218
0.233
0.250
0.268
0.287
0.308
0.330
0.354
0.379
0.406
0.435
0.467
0.500
Testing voltage for measuring the insulation resistance (V)
500
500 - 1000
1000 - 2500
2500 - 5000
5000 - 10000
Measuring temperature of
the insulation resistance
(°C)
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Correction factor of the
insulation resistance
corrected to 40 °C
0.500
0.536
0.574
0.616
0.660
0.707
0.758
0.812
0.871
0.933
1.000
1.072
1.149
1.231
1.320
1.414
1.516
1.625
1.741
1.866
2.000