.
Rotor Test
The rotor
can
be tested for grounded, open, or shorted
windings using
an
ohmmeter. Figures 8-10
and
8-11
show the rotor removed from the generator set for test-
ing. The rotor can be tested without removing it from the
generator. To gain access to the slip rings, follow the
Generator Disassembly procedures (this section)
through the fan hubassembly removal procedure. Usea
stiff wire to hold the brushes
off
the slip rings during
testing. Refer to the Brushes and Slip Ring section for
the procedures to use for inserting the wire.
If
available, it
is
recommended that a megger or insulation resistance
meter be used
for
ground tests.
Ground
Test:
To
test for grounds, set the ohmmeter for the highest
resistance scale. Touch one test prod to the rotor shaft
and hold
it
there. Touch the other test prod to one of the
slip ringsasshown in Figure8-10.Areading of lessthan
one megohm indicates the rotor isgrounded. Replacea
grounded rotor with a new rotor.
ES1764
FIGURE
8-10.
GROUNDED ROTOR TEST
Open
or
Shorted
Test:To test for open windings, set the
ohmmeter on the highest resistance scale. Place test
prods
on
the
slip
rings
as
shown
in
Figure
8-1
1. The
ohmmeter should indicate continuity between the slip
rings.
A
high resistance reading indicates a poor con-
nection or an open winding. Check the connection
between the slip rings and rotor lead wires. Replace
rotor
if
rotor winding is open.
To test for shorted winding, set the ohmmeter on the
lowest scale. Place the test prods on the slip rings as
shown in
Figure8-11.Areadingoflessthan16ohmsat
77°F
(25OC)
indicatesshorted windings. Replace rotor
if
winding
is
shorted.
If
rotor tests good proceed to stator
tests.
ES-1755
FIGURE
8-11.
OPEN
OR
SHORTED ROTOR TEST
.
8-1
3
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