4. Generator and Exciter Test
The generator fields may be tested with a “Kelvin” bridge. This is a double bridge type instrument
required for the very low resistances encountered in this test. It is understood that 0 resistance
indicates a SHORT CIRCUIT condition. An infinite resistance reading indicates an OPEN CIRCUITED
condition. See Fig. 9 below for resistance values.
NOTE: The equipment should be
COLD
or at normal ambient temperature when tests are made.
a. Disconnect generator stator leads at the power module panel.
b. Disconnect exciter leads from terminal board mounted on rear of engine control panel.
Positive lead is RED. Negative lead is YELLOW-BLACK.
c. Check resistance and compare to values given in Fig. 9.
5. Diode Test
Test values for diodes are not given here because they could be misleading. Test values may vary
even between diodes of the same part number, rating, and manufacturer. General instructions for
testing diodes follows:
a. Disconnect diode lead(s).
The regulator output must never be grounded when the generator is turning.
NOTE: For units with 10 ohm, 100 watt ballast resistors (before Jan. 1976) voltage is 30-40 V DC.
b. Use a good quality ohmmeter. An instrument which indicates 50 ohms at the center of the
scale is preferable.
NOTE: The battery must be in good condition and the pointer adjusted to zero when the test lead points are
shorted together. Set the scale selector to RX1 and “zero” the ohmmeter before testing diodes.
CAUTION
TEST CONNECTION
NOMINAL RESISTANCE IN OHMS
GENERATOR STATOR
Phase A to N *
0.00827
Phase B to N *
0.00835
Phase C to N *
0.00840
EXCITER A-B, B-C, A-C
0.1
Field
(RED to YELLOW-BLACK)
7.23
ROTATING FIELD
Measure resistance at revolving field rectifier
(CR2)
with exciter armature leads removed from
rectifier. (See Connection Diagram)
2.19
Generator and Exciter Stator Test Values
(70
o
F Ambient Temperature)
Figure 9
OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
February 28/94 Revised
Chapter 2-3
Page 15
Summary of Contents for 6921 Series
Page 2: ...This page intentionally left blank ...
Page 223: ......
Page 224: ......
Page 225: ......
Page 226: ......
Page 227: ......
Page 228: ......
Page 229: ......
Page 230: ......
Page 231: ......
Page 232: ......
Page 233: ......
Page 234: ......
Page 235: ......
Page 236: ......
Page 237: ......
Page 238: ......
Page 239: ......
Page 240: ......
Page 241: ......
Page 242: ......
Page 243: ......
Page 244: ......
Page 245: ......
Page 246: ......
Page 247: ......
Page 248: ......
Page 249: ......
Page 250: ......
Page 251: ......
Page 252: ......
Page 253: ......
Page 254: ......
Page 255: ......
Page 256: ......
Page 257: ......
Page 258: ......
Page 259: ......
Page 260: ......