7-22 Component Testing and Adjustment TP-5606 6/02
Exciter Field
The exciter field, used only on three-phase generator
sets, is magnetized by DC current. When the exciter
armature is rotated within the magnetized exciter field
windings, an electrical current develops within the
exciter armature. Test the exciter field according to the
following procedure.
1. Disconnect generator starting battery (negative
lead first) and power to battery charger (if
equipped). Disconnect plug P5 of wiring harness
from the voltage regulator.
2. Check exciter field resistance by connecting an
ohmmeter across exciter field F1 and F2 (pins 10
and 12 of P5). See Figure 7-19. The resistance
reading for a cold exciter field is found in
Specifications--Generator of Section 1. A low
reading indicates an internal short and a high
reading indicates an open winding. Repair or
replace exciter field if ohmmeter readings indicate
exciter field is defective. If resistance test proves
inconclusive, perform a megohmmeter test on
exciter field as described in the next step.
Stator
Stator
Rotor
Exciter Field
Exciter Field
Exciter
Armature
Ohmmeter
P4 P4
To
Controller
P7 P6
P1--10
P1--12
P5--10
P5--12
Voltage Regulator
F1
F2
Figure 7-19. Checking Exciter Field Resistance
Hazardous voltage.
Can cause severe injury or death.
Operate the generator set only when
all guards and electrical enclosures
areinplace.
Moving rotor.
WARNING
Hazardous voltage can cause severe injury or
death. Perform electrical service only as prescribed in
equipment manual. Be sure that generator is properly
grounded. Never touch electrical leads or appliances
with wet hands, when standing in water, or on wet
ground as the chance of electrocution is especially
prevalent under such conditions. Wiring should be
inspected at the interval recommended in the service
schedule--replace leads that are frayed or in poor
condition. The function of a generator set is to produce
electricity and wherever electricity is present, there is
the hazard of electrocution.
3. Check exciter field for a grounded condition.
Disconnect P5, P6, and P7. Using a
megohmmeter, apply 500 volts DC to F1 or F2
lead and exciter field frame. See Figure 7-20.
(Follow the instructions of the megohmmeter
manufacturer when performing this test.) A
reading of approximately 500K ohms (1/2
megohm) and higher indicates the field winding is
good. A reading of less than 500K ohms
(approximately) indicates deterioration of winding
insulation and possible current flow to ground.
Repair or replacement of the exciter field is
necessary.
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