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7) Other factors that influence the insulation resistance
<Pollution of the outer surface of the insulation body> If absorptive and deliquescent materials like acid, chloride
and etc are adhered on the surface of the insulation body, they influence the insulation resistance. Remove the for-
eign substances before the inspection. <Condensing Point> If the insulation body temperature is below the sur-
rounding temperature's dew point, moisture condensation can be preset on the insulation body surface (especially
at the crack and the groove) and influence the insulation resistance. The inspection should be taken into action
when the insulation body temperature is above the surrounding temperature's dew point. Record the dry bulb and
the wet bulb temperature surrounding air. <Absolute Humidity> Even through the insulation body temperature is
above the dew point, the atmospheric vapor influences insulation resistance. Avoid conduction test at the place
where the absolute humidity is high present.
8) Apply an electric current for a minute to the spot to be measured up insulation resistance. Read and record the
value. Apply the inspection standard when the insulation body temperature is 20 °C. (When measured at a differ-
ent temperature, use the temperature coefficient and convert the value indicated after a minute.)
9) Taking measures according to insulated condition.
Temp. of insulation body at inspection (
°C
)
Value indicated after a minute
Action
Danger
Below 2 M
Ω
Repair or Exchange
Bad
Below 50 M
Ω
Troubleshooting
Re-inspection
50~ 100 M
Ω
Troubleshooting
Good
100~500 M
Ω
Better
500~1000 M
Ω
Excellent
Above 1000 M
Ω
Condition
Insulation Absorption Rate
Danger
Below 1
Bad
Below 1,5
Re-Inspection
1.5~2
Good
2~3
Better
3~4
Excellent
Above 4
h
Motor that is within the range of "Bad" and "Re-Inspection" at the mega insulation test, must take the POLARIZA-
TION INDEX test.
10) Polarization Index Test
Record the indicated value appeared when performing the mega test after a minute and the one after 10 minutes.
If the motor's insulation absorption rate is within the range of "Danger", must be returned or replaced.
If the motor's insulation absorption rate is above the range of "Bad", must be checked additionally after 4 hours of
careful operation.
11) The following should be recorded when performing the mega test
- Type and voltage of the mega tester
- Connection part of the mega tester
- Surrounding temperature and humidity of the test taking place and the tank's internal pressure in case of her-
metic type
- Stoppage period before the inspection
Table 53. Insulation condition
Table 54. Insulation absorption rate status
Insulation Inhaling rate =
indicated value after 1 minute
indicated value after 10 minutes