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National Projector Carbons
If the arc length is decreased it will hold essentially the same arc shape, if the operating conditions are favorable, until it reaches approximately 0,23 inch or 24 volte. Figure 63 A illustrates the arc just before that point, with a good burning condition; and (B the arc just after that point, with a shorter arc length and poor burning conditions. When the arc length is 0.23-inch the arc stream begins to be turbulent. The two tail-flames and the highly luminous portion of the arc close to the electrodes lost their identity, and the whole arc assumes a boiling and seething appearance. There is rapid flicker; the arc voltage and current are erratic; and in addition, at such very short arc lengths there is a noticeable shadowing effect from the electrodes themselves.
Figure 63
8 mm A.C. High Intensity Carbons: 80 Amperes, 23 to 24
Volts; (a) Short Arc Length, Good Operating Conditions;
(b) Short Arc Length, Poor Operating Conditions
If the length of the arc is increased beyond that shown in Figure 62 the form of the arc will be sustained if the operating conditions are suitable, until the length is approximately 0.35-inch. Figure 64 (A) shows the arc immediately before, and (B) after, such a point has been reached. At and beyond that length, the arc has a tendency to be swept upward, so that the lower part no longer bows down appreciably, and the upper part and the tail-flame become greatly extended. The highly luminous portions close to the electrode likewise becomes distorted, as shown in (B). The arc is unstable to such an extent that it will repeatedly jump back and forth between the positions shown at (A) and (B).
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