Generac Power Systems 53187 - Manual (Page 35)

PARTI
THE REVOLVING FIELD AC GENERATOR
1
SECTION 1.6- TROUBLESHOOTING
(UNITS WITH 15 INCH STATOR)
Detailed Instructions (Continued)
Procedure: Gain access to the sensing trans­
form er, inside the control panel. Use a volt-ohm -m illi-
am m eter (VOM) to test the sensing transform er as
follow s:
1. Disconnect W ires No. 11 and 22 from the
transform er’s PRIM ARY term inals, to prevent interac­
tion.
2. Connect the VOM test leads across the tw o PRI­
MARY (120 volts) term inals. Resistance of this w inding
should be approxim ately 120 ohm s (plus or m inus 2%).
3. Disconnect W ires No. SI5 and SI 6 from the trans­
form er SECONDARY (240 volts) term inals, to prevent
interaction.
4. Connect the VOM test leads across the tw o SEC­
ONDARY (240 volts) term inals. Resistance should be
approxim ately 950 ohm s (plus or m inus 2%).
Results:
1. If the transform er fails the test, it should be replaced.
2. If the transform er checks good, go on to Test 10.
PRIMARY
120 VAC
[ qooop I
oaoWflÒSbì
■ 6
SECONDARY
20 VAC
Figure 5. The Sensing Transform er
TEST 10- TEST STATOR AC POW ER W INDINGS:
Discussion: An open condition in eitherof the dual
stator AC pow er w indings w ill result In loss of AC output
from the affected w inding. A shorted condition in those
w indings w ill cause a reduction in AC voltage that is
com m ensurate w ith the num ber of shorted turns. A
shorted condition can also im pose such a heavy load
on the engine that engine speed and AC frequency w ill
also drop sharply. This test w ill check the stator AC
pow er w indings for (a) an open condition, (b) a shorted
condition, and (c) a grounded condition.
Procedure: To test 1-phase, dual w inding stators,
proceed as follow s:
1. Disconnect W ires No. 11, 22, 33 and 44 from the
m ain circuit breaker (CB1) and from the unit grounding
lug.
2. Set a VOM to its ■ Rxl’’ scale and zero the m eter.
3. Test the w indings as follow s:
a. Connect the m eter test leads across W ires No. 11
and 22. Resistance reading should be approxim ately
as listed in chart in Part 6.
b. Connect the m eter test leads across W ires No. 33
and 44. Resistance reading should be approxim ately
as listed in chart in Part 6.
c. Set the VOM to a very high resistance scale, such
as 'Rxl 0,000" or "RxlK". Then, zero the m eter.
d. Make sure none of the stator leads are touching
the generator or each other at any point. Connect
one VOM test probe to W ire No. 11, the other test
probe to W ire No. 33. The VOM should read "Infinity“.
Any reading other than "infinity" indicates a short
betw een the stator w indings.
e. Connect one VOM test probe to W ire No. 11, the
other to a clean fram e ground on the stator. VOM
should read "infinity".
f. Connect one VOM test probe to W ire No. 33, the
other to a clean fram e ground. Reading should be
"infinity".
nmnrin rWiRRTi
11 22 33 44
SEE SECTION 1.5, PAGE 1.5-3 FOR
SOME OTHER STATOR CONFIGURATIONS.
ALSO SEE PART 6, PAGE 6.1-1 FOR SOME
RESISTANCE VALUES.
Figure 6. Stator W indings Schem atic
TEST 11- TEST ROTOR W INDINGS;
Discussion: An open circuit condition in the Rotor
w indings m eans that excitation current cannot flow in
the circuit. Field boost current w ill be unable to flow in
an open circuit either.
Procedure: Use a VOM to check the resistance of
Rotor w indings. Connect the positive (+) VOM test
probe to the positive (+) Rotor slip ring (nearest the
Rotor bearing). Connect the com m on (-) VOM test
probe to the negative (-) slip ring. The VOM should
indicate approxim ately as listed in the chart in Part 6
(Page 6.1-1).
Rem ove both brush holders to prevent interaction.
Set VOM to a high resistance scale and zero the m eter.
Connect the positive (+) test probe to the positive (+1
slip ring (nearest the Rotor bearino); the com m on (•)
test probe to a clean fram e ground. "Infinity" m ust be
indicated.
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