V.5 No 1

23

On physical processes in showering arcs

75 years of the birth of my Mother

Phenomena at electric contacts breaking direct-current inductive loads

After rejected application on supposed discovery

OT # 9192 registered on 27.01.1976

"Phenomenon of voltage surges as a consequence of multiply produced metallic between-contact bridges breaking inductive load"

Dyna P. Karavashkina

Senior teacher

Kharkov Radio Electronic Institute, USSR

(during working on the discovery)

S.B. Karavashkin

student

Kharkov Polytechnical Institute, USSR

(during working on the discovery)

apt. 187, bldg. 38, Prospect Gagarina, Kharkov 61140, Ukraine

Phone: +38 (057) 7370624

e-mail: selftrans@yandex.ru , selflab@mail.ru

This paper is devoted to theoretical and experimental study of physical nature of unstable discharges arising in contact gaps when opening inductive load. We revealed that despite conventional opinion, showering arcs are alternating relaxations. Each of them consists of two stages: monotonous exponential growth of voltage related to the charging of parasitic capacitance of gap which is shunted by metallic bridges, and of high-frequency high-voltage oscillation process related to the high-frequency spark process within the gap. With it, metallic bridges are produced in each period of unstable discharges. We analyse the conditions and stipulate the physics of processes of such bridges formation. We established that the cause of bridge formation is the electric pressure in high-voltage oscillation process preceding the monotonous period of unstable discharge. The second cause are plasma jets able to strap even larger gaps than those typical for unstable discharges. The experimental results obtained after this theoretical study fully corroborated the described pattern of physical processes in showering arcs. On the basis of developed method to obtain the dynamic curve of breakdown voltage and noting the experimentally corroborated physics of processes, we have successfully carried out the work on practical protection of relay contacts working under inductive load, and presented the result of this protection.

Keywords: contacts opening inductive load, short arcs, unstable discharge, showering discharge, multiple metallic bridges, contact protection from erosion

Classnames by PASC 2001: 52.80.Mg; 52.80.Pi; 52.80.Tn