7-4
Exciter Rotor
Winding Insulation Resistance: Disconnect all six
exciter rotor leads from diode terminals CR1
through CR6 and isolate them from ground. Con-
nect any lead to the megger and conduct the test as
instructed under Winding Insulation Resistance
Test Procedure.
Winding Resistance: Measure electrical resist-
ance across each pair of rotor windings: T11-T12,
T21-T22, T12-T13, T22-T23, T13-T11 and
T23-T21. See the connection schematic. Replace
the exciter rotor if the resistance of any winding is
not as specified in Table 7-1.
Rotating Rectifiers
The rotating rectifier assembly is mounted on the
back face of the exciter rotor. It consists of one posi-
tive (+) and one negative (−) diode assembly. Each
assembly carries three diodes in an epoxy potting.
Each diode has a terminal for connecting the ap-
propriate lead from the exciter rotor (CR1-CR6).
Each assembly has a field terminal (F1+ or F2−) for
connecting the leads from the main rotor (generator
field).
Diode Tests: Use the diode test function on the test
meter to test the six diodes in the rotating rectifier
assembly. Also disconnect the lead at each diode
terminal to make sure all of the meter test current
flows only through the diode being tested.
1. Test Forward Bias on Positive Rectifier Assem-
bly − Touch meter positive to field terminal F1+
and meter negative to diode terminals CR1,
CR2 and CR3.
2. Test Reverse Bias on Positive Rectifier Assem-
bly − Touch meter negative to field terminal F1+
and meter positive to diode terminals CR1,
CR2 and CR3.
3. Test Forward Bias on Negative Rectifier As-
sembly − Touch meter negative to field terminal
F2− and meter positive to diode terminals CR4,
CR5 and CR6.
4. Test Reverse Bias on Negative Rectifier As-
sembly − Touch meter positive to field terminal
F2− and meter negative to diode terminals
CR4, CR5 and CR6.
In Forward Bias the meter should indicate 0.5 to 0.8
volts. In Reverse Bias the meter should indicate
Open. Replace the rectifier assembly if the meter in-
dicates that any diode is open in both directions or is
shorted (zero ohms and/or audible signal).
Replacing Diode Assembly: Make sure the re-
placement diode assembly is of the correct polarity,
positive (+) or negative (−). Then disconnect all
leads from the defective diode assembly and re-
move the two mounting screws. Mount the new
diode assembly, reconnect all leads and torque the
terminal screws to 24 lb-in (2.6 N-m).
Redistribution or publication of this document,
by any means, is strictly prohibited.
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