Generator and Excitation Circuit
Trouble, Symptom & Condition
Test or Inspection
Corrective Action
2.
No (or low) output voltage
when operating in MANUAL
mode.
a. Defective generator
manual control excitation
circuit.
Place AUTO-MANUAL control
switch (33, Fig. 1) in AUTO
position. If a normal voltage is
NOT produced, perform checks
as instructed in GENERATOR
AND EXCITATION CIRCUIT
TROUBLE 1, above. If a normal
voltage is produced, proceed to
step “B” below
b. Defect in manual voltage
control portion of excitation
circuit.
Check as follows:
c. Defective AUTO-MANUAL
switch (33, Fig. 1).
Check contacts and operation
of AUTO- MANUAL switch.
Replace if defective.
d. Defective rectifier (CR3)
(Sect. 1-1; 14, Fig. 8).
Check diodes (see 2-3, Para..
6). Replace rectifier if defective.
e. Defective resistor (R11)
(See 1, Fig. 5).
Jumper resistor (1, Fig. 5). If
normal voltage (depending on
rheostat) is produced, replace
resistor.
f. Defective rheostat (R61)
(32, Fig. 1)
Connect a jumper across
rheostat. If maximum (manual
control) voltage is produced,
replace rheostat.
3.
Load contactor (K1) will not
close when control switch (20,
Fig. 1 is held in CLOSE
position. Generator running at
normal voltage. No fault lights
on.
a. In addition to defective
wiring and connections in
the AC and DC load
contactor actuating circuits,
the load contactor may be
prevented from closing for
any of the following reasons:
After checking fuse (F1) in step
(1) below, check all wiring and
connections in the load
contactor circuits on the engine
control panel, the protective
relay tray and power module.
Then check components as
follows:
b. Blown fuse (F1) )1-1; 16,
Fig. 9)
Remove and inspect fuse.
Replace if blown.
c. Defective (open) relay in
protective module (1-1; 4,
Fig. 9).
Use a jumper with clip and prod
terminals to GROUND terminal
“H” in the test receptacle. If
contactor will now close,
replace module or complete
protective relay tray (12, Fig. 1)
OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
February 28/94 Revised
Chapter 3-1
Page 19
Summary of Contents for 6921 Series
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