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Be GENERATOR SINGLE PHASE
TESTING THE EXCITER WINDINGS
Single
Capacitor
1.9 Ohms
Dual
Exciter
2.2 Ohms
An AC voltage is induced in these windings by the rotating
field. Checking the residual voltage output from this winding
can detennine the condition of the winding when troubleshoot-
ing.
RESIDUAl VOLTAGE:
Single Capacilor Model:
10· 14 Volls AC from each winding
Dual Exciter Model:
7 -
9 Volts AC from each winding
AC voltage can be measured across the capacilor(s) while the
generator is operating. This voltage may be as high as 400 to
500 volts AC. This voltage buildup is accomplished as the
exciter windings charge the capacitor(s) and the capacitor(s)
discharge back into the exciter windings. This AC voltage
reading is taken between the #60 Hertz connector and the
#
connection plugged into the capacitor(s) while the generator
is operating at its rated Hertz (61.5 - 62.0). This flow of satu-
rating AC in the exciter windings produces a phase-imbal-
ance type of field that effects the auxiliary windings: a
beneficial result that produces good motor starting characler-
istics for this type of generator.
To measure the resistance value of the exciter windings,
locate the #9 and the #50 Hertz capacitor connections.
NOTE: Three numbered capacitor connections exist: #7, #8,
and
#9;
and two Hertz connections, #50 and #60.
Unplug any other connections from the capacitor(s) noting
their position on the capacitor. Place one lead of the ohmme-
ter on plug connection #9 and the other lead on plug connec-
tion #50 Hertz. Measure the resistance value of the exciter
windings. Check to make sure there is no continuity to the
ground/generator case from either of the two leads. Also
check that no continuity exists between either the #50 Hertz
plug or the #9 plug and any of the main stator windings leads
on the AC tenninal block. If continuity is found here, a fault
exists between these two winding groups.
FIELD-TESTING THE CAPACITOR
With a capacitor meter, test the capacitor following the
instructions included with the meter, and compare the results
with the value shown on the capacitor. \Vhen a capacitor
meter is not available, perform the following simple test:
1,
Marking them so they may be reattached correctly.
unplug the connections from the capacitor.
2. With a jumper, short across the two connections exposed
in the previous step. TIris ensures the capacitor is dis-
charged as it would be at shutdown.
3. With an ohmmeter set on the high R scale, place its plus
(+) lead on one capacitor connection and the negative (-)
lead on the other capacitor connection. A resistance
should be read and should rise slowly as the meter
attempts to charge the capacitor. This indicates a
presumably good capacitor.
4. Indications of a defective capacitor:
a. Zero resistance or no rise in resistance value (shorted
capacitor).
b. Infinite resistance (open capacitor).
c. No continuity should be found between the capacitor's
connections and the capacitor's case or base.
s.
Capacitor Ratings .(Capacitor meter)
a. Single Capacitor Units: 25.0 microfarads (uP) 5'
b. Dual Capacitor Units: 31.5 microfarads (uP) 5'
NOTE:
The
capacitor rating is marked on the housing of the
capacitor:
25.0 Microfarad capacitor PN 035985
31.5 Microfarad capacitor PN 035978.
6. 12 volt DC excitation (low or no AC output voltage) the
generator may be excited using 12 volts DC taken from
the engine's starting battery. This voltage is applied
across the #50 and #9 leads of the exciter circuit wind-
ings with any other numbered leads unplugged from the
capacitors(s). The generator's reaction during flashing
will help detennine its fault.
7. During 12 volt excitation, output voltage ranges are as
follows:
Single
Capacitor
22-26VAC
Dual
Exciter
12-14 VAC
a. A slight rise in the output voltage with the loading of
the engine andlor a growling noise from the generator
end will indicate a fault in the main stator windings.
h. No rise or very slight rise in the output voltage will
indicate a fault in the exciter windings.
c. Normal output voltage as specified above, check
exciter circuit capacitor(s).
(+)12 VDC
50Hz
LEAD
60Hz
LEAD
(·)12 VDC
Engines
&
Generators
41
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