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Be GENERATOR SINGLE PHASE
Testing Component Resistance Values
Rotating Field/Auxiliary Windings and Diodes
Two sets of windings are found in the rotor assembly. An AC
voltage is produced in two groups of windings as the rotor
turns at rated rpm. The AC voltage passes through each of
the two diodes mounted on the isolated fixture just before the
rotor carrier bearing. The AC sine wave is changed to a DC
and this DC voltage is passed through the two groups of
rotating field windings producing a DC field around these
windings. This field affects the AC winding of. the two main
stator groups inducing an AC voltage in these windings that
is available at the AC terminal block connections.
DIODE
1. Rotating Field! Auxiliary Windings
Single Capacitor
3.8 Ohm - Dual Excitor _ 4.0 Ohm
To check the resistance values, rotate the engine's crank-
shaft to position the diode(s) on the generator's shaft at
12
0'
clock. To make a quick check of these windings,
presume the diode is OK and place one of the ohmme-
ter's leads on the connection at the top of the diode and
the other lead at the connection at the base of the diode.
Compare readings with the value above. If a distinct dif-
ference is noted in the ohm value, carefully unsolder the
lead on the top of the diode and remove the diode from
its isolated heat sink using a thin walled, deep well 7116
in (II mm) socket.
NOTE: The aluminum heat sink that the diode threads into
can be bent carefully outboard to make easier access to
the diode.
With the diode removed, both leads for the first group of
rotating field/auxiliary windings will be isolated with no
interference from a possibly faulty diode.
Check the resistance value of the rotating windings by
placing the ohmmeter's leads across the two exposed
leads.
Also, verify that no continuity exists between these wind-
ings and the rotor shaft by leaving one ohmmeter lead
attached to the winding lead and the other ohmmeter lead
touching the shaft: no continuity should exist. If continu-
ity is found, a short exists ..
Repeat this same check on the second group of windings.
Rotate the engine's crankshaft 180
0
to position the sec-
ond diode and connections at 12 o'clock.
No continuity should be found between these two groups
of windings.
2. Diodes 8 - 9.5 ohms (approximate) using a 260 Simpson
Analog Meter
To check the diode, unsolder the connection from the top
of the diode. Place one ohmmeter lead on the connection
at the top of the diode and the other ohmmeter lead to the
diode's base. Then reverse the position of the ohmmeter
leads.
DIODE
H
(+)
LOW RESISTANCE
A low resistance should be found with the leads in one
direction, and infinite resistance (blocking) in the other
direction. Different meters will read different resistance
values through the diode.
NOTE: Different meter models may show different ohm
values, but should read the same for both diodes.
Diode Rating: 1600 amps 26 Amps
The diode's rating is far in excess of the circuit's require-
ments. Most likely a diode failure will result from an
overspeed or load surge.
Main Stator Windings
Single
Capacitor
0.6 Ohms
Dual
Excitor
0.5 Ohms
Residual voltage measured between # 1-#3 and #4-#6 will be
2-3 volts AC between each pair of leads at the terntinal
block. This would be an indication that the stator windings
are okay. Check exciter windings and artificially excite the
generator.
NOTE:
THE NUMBERED LEADS ON THE
TERMINAL BLOCK ARE NOT IN ANY NUMERICAL
ORDER. THEY ARE AS SHOWN BELOW
,
,
3
0 0 0
,
2
6
0 0 0
TERMIIIIALliLD.C.K
Group #1 - Measure resistance value betw.een terntinal with
lead #1 and terntinal with lead #3. (Check that there is no
continuity of Group #1 windings to the case ground.)
Group #2 - Measure resistance value between terntinal with
lead #4 and terminal with lead #6. (Check that there is no
continuity of Group #2 windings to the case ground.)
Check for a possible short between the two groups of stator
windings by placing one lead of the ohmmeter on the ternti-
nal with the stator lead #3 and the other ohmmeter lead on
the terntinal with stator lead #6. There should be no continu-
ity between the two groups of stator windings.
Engines
&
Generators
42
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