V.5 No 1

43

On physical processes in showering arcs

7. Area of scientific and practical use of the discovery

In the scientific plane this discovery will allow to develop the correct physical understanding of phenomena taking place in the contact gaps during opening inductive loads.

Undoubtedly, this representation will require also to re-consider and to correct the main positions of theory of power arc processes and of the erosion causes which they rise.

On the basis of new theory, the scientists will develop the new models of contacts erosion and dynamic breakdown voltage, which will be more perfect and more consistent with experiments. These models will enable us to predict better the longevity of contact elements and their reliability.

On the basis of new theory, we can develop more perfect and more consistent with experiments models of contact erosion and of dynamic breakdown voltage. These models will allow better quality of predictions of longevity and reliability of contact elements.

In its turn, more correct physical understanding of phenomena occurring in contacts will enable to develop better methods and devices for experimental studies, in that number for spark processes study.

This discovery will largely contribute to engineering. One of its practical outputs is the technique to obtain the dynamic curves of breakdown voltage. Such curves will allow the optimal selection of both circuits protecting the contacts from erosion and their parameters. This engineering problem is still unsolved because of lack of breakdown voltage curves and the very practically available technique to obtain them.

To bring to life this new perspective towards the development of method to obtain the curve of breakdown voltage and following synthesis of circuits protecting elements from erosion, one of the authors statistically worked the curves of breakdown voltage obtained on the basis of stated here method, and on the basis of these curves made the synthesis of spark-extinguishing circuits for low-power contacts. Thereupon were obtained oscillograms of contact elements opening practically without showering arcs. Two most typical oscillograms are shown in Fig. 27.

a)

b)

Fig. 27. Oscillograms of transients when opening contacts protected by the spark-extinguishing circuit

As seen in these oscillograms, correctly synthesised spark-extinguishing circuit is able to almost lift the showering arcs and in this way to considerably decrease the mass transfer and contact erosion. The only, it is quite difficult to exclude the stage of short arc (see Fig. 27 b) that does not inscribe into general conditions of protection developed on the basis of dynamic curve of breakdown voltage. Here we have to account the regularities causing the short arcing. In Fig. 28 we show the combined oscillogram of current and voltage; it corroborates, to prevent short arcs, we have additionally to account the current characteristics of short arcing.

Fig. 28. Combined oscillogram of current (upper curve) and voltage (lower curve) for transients at the contacts protected by the spark-extinguishing circuit

In this oscillogram we see that with process relatively smooth in the view of at- contacts-voltage curve, the curve of current in the region of short arcs has essential splashes and over-oscillations which cannot be controlled after the voltage curve; consequently, they cannot be accounted in spark-extinguishing circuit synthesis.