Iniciranje i razvoj proboja u tačkama levo od Pašenovog minimuma
Initiation and progress of breakdown in range to the left of the paschen minimum.
Докторанд
Jovanović, BojanМентор
Osmokrović, PredragЧланови комисије
Cvetić, JovanVasić-Milovanović, Aleksandra
Vujisić, Miloš
Stanković, Koviljka
Метаподаци
Приказ свих података о дисертацијиСажетак
Pašenovom krivom se prikazuje zavisnost vrednosti probojnog napona dvoelektrodnog
sistema izolovanog gasom od proizvoda pritiska (p) i meĊuelektrodnog rastojanja (d).
Jednoznaĉna zavisnost vrednosti dc probojnog napona od proizvoda pd direktna je
posledica vaţenja zakona sliĉnosti za elektriĉno praţnjenje u gasovima. Pašenova kriva
ima oblik asimetriĉne U-krive sa izrazitim minimumom koji se naziva Pašenovim
minimumom. Pašenov minimum je odreĊen vrednošću pritiska gasa (tj. gustine) pri
kojoj Tausendov jonizacioni koeficijent ima maksimalnu vrednost u zavisnosti od
odnosa meĊuelektrodnog rastojanja srednje slobodne duţine puta elektrona. U taĉkama
desno od Pašenovog minimuma dc probojni napon se moţe, uslovno, smatrati
deterministiĉkom veliĉinom tj. veliĉinom prilikom ĉijeg odreĊivanja je dominantna
merna nesigurnost tip B. To je posledica ĉinjenice da se u taĉkama desno od Pašenovog
minimuma dc proboj odvija samoodrţavajućim gasnim multiplikativnim procesom uz
vremensku konstatu prome...ne napona mnogo veću od vremena karakteristiĉnog za
odvijanje elementarnih procesa gasnog praţnjenja. U taĉkama levo od Pašenovog
minimuma dc proboj se odvija kombinacijom gasnih mehanizama i vakuumskih
mehanizmima, a javlja se i takozvani anomalni Pašenov efekat. To uslovljava da dc
probojni napon u taĉkama levo od Pašenovog minimuma bude statistiĉka veliĉina tj.
veliĉina prilikom ĉijeg odreĊivanja je dominantna merna nesigurnost tip A. Vrednost
impulsnog probojnog napona je stohastiĉka veliĉina i levo i desno od Pašenovog
minimuma. To je posledica ĉinjenice da je vremenska konstanta promene impulsnog
napona istog reda veliĉine kao vreme karakteristiĉno za odvijanje elementarnih proces
gasnog praţnjenja. U radu se razmatraju mehanizmi iniciranja i razvoja proboja gasova
u taĉkama levo od Pašenovog minimuma. Statistiĉkom analizom eksperimentalnih
rezultata, dobijenih pod dobro kontrolisanim laboratirijskim uslovima, pokazano je da
se oblast levo od Pašenovog minimuma moţe, uslovno, podeliti na tri podoblasti.
Pokazano je da se u prvoj podoblasti, neposredno uz Pašenov minimum proboj odvija se
iviĉnim mehanizmima ĉesto tumaĉenim kao anomalni Pašenov efekat. U sledećoj
podoblasti do proboja dolazi vakuumskim mehanizmom lavinskog tipa, a u trećoj
podoblasti proboj se odvija vakuumskim emisionim mehanizmom katodnog tipa.
Paschen curve illustrates the dependence of the breakdown voltage of a gas insulated
two-electrode system on the product of pressure (p) and inter-electrode distance (d). The
validity of the similarity law for gas electrical breakdown produces direct dependence of
the dc breakdown voltage on the pd product. Paschen curve is an asymmetrical U shape
with a prominent minimum, called the Paschen minimum. The Paschen minimum
corresponds to the gas pressure (i.e. density) at which the Townsend ionization
coefficient is largest, with respect to the ratio between the inter-electrode distance and
the electron mean free path.
The dc breakdown voltage which occurs in the region to the right of the Paschen
minimum, can be regarded as a deterministic quantity, i.e. a quantity for which type B
uncertainty dominates its measurement. This results from the fact that to the right of the
Paschen minimum dc breakdown occurs via self-sustained multiplication process in the
gas, where the time constant of v...oltage change is much greater than the time
characteristic of elementary gas discharge processes. In the range to the left of the
Paschen minimum, dc breakdown occurs through a combination of gas mechanisms and
vacuum mechanisms, and also as the so called anomalous Paschen effect. Because of
this, in the range to the left of the Paschen minimum the dc breakdown voltage is a
stochastic quantity, i.e. a quantity for which type A measurement uncertainty is
dominant. The impulse breakdown voltage value is stochastic both to the left and to the
right of the Paschen minimum. This derives from the fact that the time constant of a
voltage pulse change is on the same order of magnitude as the time characteristic of
elementary gas discharge processes. Mechanisms of gas breakdown initiation and
development in the range to the left of the Paschen minimum are investigated in this
paper. Experiments were conducted for gas pressures from 10-9
to 10-1
bar and interelectrode
gaps from 0.1 to 1 mm. The statistical analysis shows that the region left of
the Paschen minimum can be divided into three subregions. It is established that the so
called anomalous Paschen effect refers to breakdown occuring by way of the edge
mechanisms in the first subregion, just next to the Paschen minimum. In the second
subregion, breakdown emerges through the vacuum avalanche mechanism, and in the
third subregion it occurs through the vacuum cathode emission mechanism.