Protective Circuit (Continued)
Trouble, Symptom & Condition
Test or Inspection
Corrective Action
Load contactor opens during
power delivery. Indicating light
ON
a. One of the resistors (R26,
R27 or R28) across
overload transformer is
open Circuited.
An open resistor will cause a
higher than normal Voltage.
Check Resistors (Sect. 1-1; 1,
Fig. 13). Replace if defective.
b. Overload device printed
circuit board defective.
With unit off, measure
resistance between terminals B
and E, Fig. 8. If zero ohms
resistance is measured, replace
Overload device (K4)(Section
1-1; 7, Fig. 11).
Generator
Trouble, Symptom & Condition
Test or Inspection
Corrective Action
1.
No (or low) voltage output.
a. Shorted diode in exciter
rectifier (CR2).
Check diodes in accordance
with sect. 2-3, Para. 6 If diodes
are good, proceed to step B.
b. Open or shorted exciter
rotor winding (G2).
Use ohmmeter to check for
open or shorted condition. If
rotor windings are good,
proceed to step C.
c. Open or shorted exciter
field windings (L2).
Check for field resistance. See
Sect. 2-3. Fig. 14 for normal
values.
d. Open or shorted generator
rotor windings (L1).
Check resistance with
ohmmeter to determine if open
or short circuited.
2.
Generator operates single
phase.
a. An open or short circuited
winding in generator stator
(G1).
Check stator winding
resistances. See Sect. 2-3, Fig.
12 for normal values.
3.
Generator overheats.
a. Loose connection causing
high resistance.
Check all output connections for
looseness. Look for
discoloration caused by heat.
Tighten or replace as required.
b. Improper or blocked
ventilation.
Check for foreign materials
(rags, etc.) blocking air flow.
Provide adequate ventilation.
c. Check Stator windings
short circuited.
Check Stator windings. See
Sect. 2-3, Fig 12.
OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
Chapter 3-1
February 28/94 Revised
Page 24
Summary of Contents for 6921 Series
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