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Make up the circuit of Fig. 4 with the ground switch of the
device in the closed position, which de-energizes the device.
Place all of the rotary switches and the toggle switch of the
phase angle adjustment in the zero position and set the
voltage adjustment dials to maximum (which is primary
voltage and hence will give the minimum output voltage).
Next open the device ground switch and shift the voltage
adjustment dials to obtain approximately 115 volts S1 to S3.
Note the oscilloscope trace; it is very probably an approximate
ellipse. To determine which direction to proceed from here,
switch in 24 or 48 turns of the phase angle adjustment and
then note the position of the buck-boost switch which gives
the nearest to a straight line trace on the oscilloscope. This
simple check should establish the correct position of the
buck-boost switch and then the finer adjustments of the
phase angle switches is a straight forward procedure to secure a
Figure 4: Test Circuit Using Oscilloscope
8
straight line trace on the oscilloscope. Start by first trying the
larger steps (192 turns is the largest step) and if any step is in
excess of that required then drop back to the next lower turns
in the same switch. For example, with the three rotary switches
in the zero position, and if 192 is then found to be excessive
then return the toggle switch to zero and try 144 turns on the
top rotary switch. If this is still excessive then turn the top
rotary switch back down to 96 turns, and so on, until some
points is reached which is short of the required amount. Then
proceed to the middle and lower rotary switches in order until
the closest setting is reached. The total number of turns
tapped in is the sum of the settings on the three rotary
switches and the 0 to 192 toggle switch. Reference to figure
5 will give an idea of the effect of the various number of turns
of the reactance winding, both buck and boost.
ABB
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