Simultaneous Operation Of 28.5-V T-R's; Simultaneous 28.5-V Dc And; Simultaneous 112-V Dc And 115-V Ac; Test Box Operation - Hobart 6921 Series Operation And Maintenance Manual

OM-2040 / Operation and Maintenance Manual
90D20 / Generator Sets
b. Simultaneous Operation of 28.5-V T-R's
Two 28.5 V T-R's may be operated at the same time without special precautions. Prepare the
generator set for power delivery in accordance with Para. 2, D. above. Operate each T-R according
to Instructions in applicable TM.
NOTE: It is NORMAL for T-R output to become SLIGHTLY unstable indicated by blinking contactor light
on either T-R) when operating with current limiting. When output is unstable, observe DC
voltmeter. Fluctuation of one or two volts is normal.
If fluctuation is violent (several volts) , adjust voltage regulator RATE potentiometer to correct.
c. Simultaneous 28.5-V DC and 115-V AC Power Delivery
If both 28.5-V DC and 115-V AC must be delivered at the same time, the following rules and
precautions must be observed.
(1) Place T-R current limiting switch in OFF position. This will eliminate the soft start feature of the
T-R, but will prevent AC voltage from dropping low enough to trip the AC load contactor.
(2) Line-drop compensation on the T-R must be REDUCED or TURNED DOWN completely to
prevent opening of the AC load contactor by an overvoltage condition. Readjust T-R line-drop
compensation so that AC voltage (as indicated by the generator set voltmeter) does not exceed
118-V AC when the DC load is 500 Amperes. If higher DC voltage is needed, adjust T-R
line-drop compensation as required. Observe AC voltage while making this adjustment to be
certain that it does not go TOO HIGH with DC load.
(3) During simultaneous, continuous operation, loads on either circuit are limited only by the
capacities of their respective circuits, however, the combined loads should not exceed the rated
capacity of the generator set (90 kVA or 72 KW) .
d. Simultaneous 112-V DC and 115-V AC Power Delivery
Since 112-V T-R's don't have line-drop compensation capability, no special adjustment to the T-R
will be required. Combined loads should not exceed the rated capacity of the generator set (90 kVA
or 72 KW).

4. Test Box Operation

The test box is useful and convenient in testing the generator set after repair or overhaul and also in
troubleshooting. To operate the test box, proceed as follows:
a. Open left, front canopy doors and connect the test box plug connector (see 1-1; 3, Figure 14)
to the test receptacle connector (Fig. 4).
b. Connect the test probes of a voltmeter of the test jacks (3 and 4, Fig.3) . Test jacks are color
coded. Red indicates POSITIVE. BLACK indicates NEGATIVE.
c. Locate the component or circuit to be tested in the DESCRIPTION column on the instruction
plate and set the selector switch (1, Fig. 3) to the number indicated opposite the description.
d. Note the normal voltage value and kind of current (AC or DC) to be expected at the position
and set voltmeter accordingly.
e. Comply with conditions indicated in CONDITIONS column for the particular test being
performed.
f. Press the pushbutton switch (2, Fig, 3) and observe voltage indicated by the voltmeter.
Compare to normal voltage indicated in VOLTAGE column.
g. Release pushbutton switch.
h. Repeat steps A thru G for other tests as required.
i. When tests are completed, disconnect the test equipment and close canopy doors.
February 28/94 Revised Chapter 1-3
Page 7