IEEE Power & Energy Magazine - January/February 2018 - 61
the force from S1. because S2 is wired
across the arc gap, its weakening effect
is in proportion to the length of the gap;
the larger the gap, the greater the voltage across it, and so the more magnetizing current flows in S1. this weakened
force allows gravity to begin to move
the upper electrode down, closing the
arc gap and reducing the weakening effect of S2. this re-establishes the original balance between the two magnetic
fields and brings the gap back to the
proper length. this is an early example of electrical feedback control.
Figure 6 shows how the upper electrode moves. Notice that the lower
electrode is fixed and does not move.
the distances in the figure are greatly
exaggerated to show how the control
operates. In actual operation within
the bounds set by friction, the gap is always changing, and the control sys-
tem (S1 versus S2) is working to bring
it back to the correct gap.
In Figure 6, at a, the arc is burning
and the gap is in the control range. at b,
however, the gap has widened to the point
where the arc is not capable of efficiently
producing light. the voltage across the
arc gap increases and, as described previously, causes the upper electrode to move
down to close the gap at C. Notice that the
top of the electrode at C has moved down
as well. the upper electrode has been
shortened as a result of the consumption
of its carbon in the arc.
the process begins again at D, where
we see that more carbon has been consumed, and the arc has lengthened to
the point where control action is again
initiated. at e, the proper arc gap length
has been restored. Now, however, the
length of control that the solenoid can
accomplish has reached its limit. this
A
B
C
D
E
F
G
figure 6. A carbon feed sequence of
control. (From R. Barnett, The Historical
Technologist. Niagara Falls, ON, NSIH,
1986, p. 36, used with permission.)
control range is the limit of the length
of stroke that the solenoids can accommodate, no more than a few inches.
the carbons, however, are in the order
of 24-in long to allow them to burn for
the length of darkness present where
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january/february 2018
ieee power & energy magazine
61
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2018
Contents
IEEE Power & Energy Magazine - January/February 2018 - Intro
IEEE Power & Energy Magazine - January/February 2018 - Cover1
IEEE Power & Energy Magazine - January/February 2018 - Cover2
IEEE Power & Energy Magazine - January/February 2018 - Contents
IEEE Power & Energy Magazine - January/February 2018 - 2
IEEE Power & Energy Magazine - January/February 2018 - 3
IEEE Power & Energy Magazine - January/February 2018 - 4
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IEEE Power & Energy Magazine - January/February 2018 - Cover3
IEEE Power & Energy Magazine - January/February 2018 - Cover4
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