V.5 No 1

37

On physical processes in showering arcs

Before studying the region of metallic bridges formation, we made the following suppositions. A metallic bridge has to form during the high-frequency oscillation process at the contacts. If a resistance is rapidly included into the oscillating circuit, this would abruptly change the pattern of high-frequency oscillations in it - high-amplitude oscillations have to be substituted by fast-attenuating oscillations of small amplitude. The instant of this change has to be seen in the oscillogram. Typical oscillograms registering the regions of bridge formation have been photographed with the feeding source inserted straight; they are shown in Fig. 21.

a)

b)

c)

Fig. 21. Oscillograms of the showering arc sections registering the abrupt transition from the high-voltage oscillations to exponentially attenuating low-voltage oscillations in the beginning of monotonous section of charging of gap parasitic capacitance

In these oscillograms, there are well seen the regions of abrupt transition from high-amplitude high-frequency oscillations to those small, corroborating the premise that a metallic bridge is inserted into the oscillation discharge circuit of parasitic capacitance. At the same time we can see in these oscillograms some things that we substantiated above. First of all, in Fig. 21 we clearly see that with shunted gap and abrupt fall of oscillation amplitude, the shape of oscillations became harmonic, and this also corroborates our statement that high-voltage oscillations are limited by high-frequency discharge. As soon as the oscillation amplitude felt to the limits in which the high-frequency breakdown became impossible, the harmonic shape has recovered. Secondly, in each oscillogram of Fig. 21 we have registered the region of bridge breakage. So we see these processes simultaneously, which is important in the view of integer understanding of the process of bridge formation and breakage. And we see that exponential section can begin both with positive (Fig. 21 a) and negative (Fig. 21 b) voltage at the contacts, and even with zero (Fig. 21 c). And the curve of monotonous section without any deformation goes through zero point and finishes in the positive voltage region. As we already analysed above, no one physical process, except metallic bridges - conception which we have substantiated above - is able to provide the amount of properties which are observed in the experiment. This fully corroborates the hypothesis which we are substantiating.