7-2
TESTING GENERATOR
Winding Insulation Resistance Test
Procedure
A 500 VAC megger is recommended for the winding
insulation resistance tests prescribed below. A test
consists of applying the test potential between the
winding and ground (winding laminations) for a peri-
od of 10 minutes and recording resistance at 1 min-
ute and again at 10 minutes.
Resistance values of at least 5 megohms should be
obtained for a new generator with dry windings. The
polarization index should also be at least 2 (the ratio
of the resistance reading at ten minutes to the read-
ing at one minute). For a set that has been in ser-
vice, the resistance reading should not be less than
1 megohm nor the polarization index less than 2.
Dry the windings if low readings are obtained or the
set has been in standby for a long time in high hu-
midity conditions and repeat the test.
Winding Resistance Test Procedure
Use a digital ohmmeter or Wheatstone bridge to
measure winding resistance. The device should
have a precision of at least 0.01 ohm.
Break-Out Tool 300-5512
Break-out tool 300-5512 for use in conjunction with
an accurate digital multi-meter is available for pre-
forming stator winding output tests while running the
genset. The tool is plugged into the genset wiring
harness in place of the genset control. Follow the
tool instructions.
Redistribution or publication of this document,
by any means, is strictly prohibited.
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