7. Disconnect the voltage transformer leads of the
control panel (T1, T2 and T3).
8. Disconnect any sensing leads from the switchgear.
Disconnect any sensing leads from other devices.
9. Connect the megohmmeter's RED lead to ground.
10. Connect the megohmmeter's BLACK lead to “T0”
.
11. For units that are 600 volts or less, set the voltage
to 500 Volts. For units that are more than 600
volts, set the voltage to 1000 Volts.
12. Use the 30/60 Time Resistance Method:
a. Apply voltage.
b. Observe the readings at 30 seconds. Observe
the readings at 60 seconds.
c. Record the 60 second reading. This reading
must be corrected for temperature.
d. Record temperature.
e. Record humidity.
f. Remove voltage.
13. Evaluate the readings. The actual value of the
resistance may vary greatly between generators.
For this reason, the insulation's condition must be
evaluated. Base this evaluation on the comparison
between the 60 second resistance readings and
the readings that were taken on previous dates.
These two readings must be taken under similar
conditions. If a 60 second resistance reading has
a 50% reduction from the previous reading, the
insulation may have absorbed too much moisture.
14. Switch the megohmmeter to the “OFF” position.
This will discharge the megohmmeter leads.
Disconnect the megohmmeter leads.
Note: The results from the insulation resistance
checks indicate when cleaning and/or repairing is
becoming critical. Generally, insulation resistance will
vary greatly with temperature. Therefore, always test
at the same temperature and humidity. Refer to
Illustration 118 .
Engine Serial Number
Generator Serial Number
142
SEBU7125-13
Maintenance Section
Insulation - Test
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