THE CORRELATION OF LOCAL VOLTAGE AND CROSS-SECTIONAL AREAS FOR VERY HIGH CURRENT GAS BLAST ARCS IN AIR AND SF6

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THE CORRELATION OF LOCAL VOLTAGE AND CROSS-SECTIONAL AREAS FOR VERY HIGH CURRENT GAS BLAST ARCS IN AIR AND SF6

G. Jones, M. Smith, M. Irie, H. Walmsley, D. Strachan

To cite this version:

G. Jones, M. Smith, M. Irie, H. Walmsley, D. Strachan. THE CORRELATION OF LOCAL VOLTAGE AND CROSS-SECTIONAL AREAS FOR VERY HIGH CURRENT GAS BLAST ARCS IN AIR AND SF6. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-269-C7-270.

�10.1051/jphyscol:19797132�. �jpa-00219105�

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JOURUAL DE PHYSIQUE CoZZoque C7, suppument au n07, Tome

40,

JuiZZet 1979,page C7-

269

THE CORRELATION OF LOCAL VOLTAGE AND CROSSSECTIONAL AREAS FOR VERY HIGH CURRENT GAS BLAST ARCS IN AIR AND

SF6

G.R. Jones, M.R. Smith, M. Irie,

H.

L. ~ a l m s l e ~ ' and D.C. ~trachan'.

Department of EZectricaZ Engineering

&

E k c t r o n i c s , University of LiverpooZ, Liverpool L69

3BX,

h - l d .

SheZZ Research Ltd., Thomzton Research Centre,

P.

0. Box

1,

Chester, England.

1

.

INTRODUCTION. tests being performed for each representative Recent developments of the boundary layer condition.

integral analysis (e.g. (1)) for gas blast arc High speed photographs of the arc were taken modelling have highlighted the importance of with a Beckman-Yhitley Dynafax

350

framing camera

correlating the local arc voltages and the cross-

4

at framing rates of 1

-

2 x 10 pps, exposure times sectional areas of such arc columns. This paper ,of

1.3 -

2.6 ps and an aperture of f/22. Adequate presents experimental results which are examined exposure was ensured using appropriate neutral to determine whether such a simple correlation

exists for very high current gas blast arcs as has already been demonstrated for current levels

;f a few ki1oaiiiper.a~ (2).

2. EXPGRIMLNTAL CONEITIONS AND IiELbUREblLNTS.

The results presented are for arc discharges sustained by alternating current waveforms of frequency 80Hz and peak currents

40 -

9OkA. The discharges were confined to burn in axially accelerating flows of air or SF6 passing through a 50mm diameter, 3Omm wide orifice and sustained by upstream and downstream pressures of

7.8

bar and

density filters.

The arc current, overall arc voltage and upstream pressure were monitored respectively with a 0.2m coaxial shunt, a Tektronix type F6015 voltage probe and a Kistler 601A pressure trans- ducer in conjunction with a 5001,charge amplifier.

3.

EXPkXIb~k;NTAL WbULTS

.

Typical averaced results scatter) for the axial evolution of the cross-sectional area of the luminous arc core for different instantaneous current values are shown on Fig.1 for both air and SF6.

1 bar respectively. The upstream electrode (sin-

,

I

L

IlriP* I ^I

tered copper-tungsten mixture) was cathodic during the arcing half cycle.

Voltages at different axial positions along the arc'were measured using a 2mm diameter tung-

_________---

sten rod penetrating radially into the arc column,

and biased electrically to draw electron current. -4ir --SF' I l i a 1 psiu* h m )

Fic.

-

1 Only a small number of local voltage measurements

were taken under the present operating conditions Since steep temperature gradients exist at the on account of the limited probe life, combined core boundary of such arcs (e.g.

(3))

the mea- with the limited reproducibility of the arcing sured luminous boundaries should also approxi- conditions which necessitated a large number of mately coincide with the electrical boundary (21,

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797132

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provided t h e r e a r e no s u b s t a n t i a l d e p a r t u r e s from l o c a l thermal e q u i l i b r i u m .

The 70kA curve ( F i g . l ) which corresponds t o an i n s t a n t f o l l o w i n g t h e 9OkA peak c u r r e n t curve a l s o given on t h e same f i g u r e , shows an anomalous luminous a r e a v a r i a t i o n downstream of t h e nozzle e x i t which i s due t o s e v e r e e v a p o r a t i o n of t h e nozzle w a l l caused by i n t e n s e r a d i a t i v e h e a t i n g .

The measured v a l u e s of t h e e l e c t r i c a l c o r e a r e a O ( z ) (Fig.?) may be used i n c o n j u n c t i o n w i t h a simple channel a r c model ( e l e c t r i c a l conducti- v i t y , 6

,

r a d i a l l y c o n s t a n t ) t o g i v e l o c a l v o l t a g e v a l u e s V(z) according t o

V(

z) =

( r / a ) % [ ~

(z)J

where i i s t h e i n s t a n t a n e o u s c u r r e n t . For a channel temperature of 2 x 1 0 4 K (31, 6 = 100 ( a i r ( 4 ) ) and 105srn-' (SF6 ( 5 ) ) b e i n g r e l a t i v e l y i n s e n s i t i v e t o p r e s s u r e ( (41, ( 5 ) ) and concentra- t i o n of evaporated m e t a l l i c i m p u r i t i e s ( (31, ( 6 )

1.

The r e s u l t i n g v o l t a g e v a l u e s a r e g e n e r a l l y i n good agreement with t h e d i r e c t l y measured v a l u e s f o r a l l c u r r e n t s i n SF6 (Fig.2) and f o r 41kA i n a i r (Fig.3).

f I ;

,

Î ÎI Î I

, i I

, ~ - i 1

n I n I u t w ^I

I

^w

Amil psilir h.1

F i g . 2

Good agreement with t h e o v e r a l l a r c v o l t a g e (516V) f o r 7OkA i n a i r is o b t a i n e d o n l y i f i t is ^assumed t h a t t h e f u l l luminous e x t e n t , i n c l u d i n g t h e plasma produced by t h e n o z z l e a b l a t i o n downstream of t h e n o z z l e e x i t , i s taken i n t o account a s t h e e l e c t r i c a l l y conducting c r o s s - s e c t i o n . The d e r i v e d v a l u e of o v e r a l l a r c v o l t a g e (900V) f o r t h e 90kA a r c i n a i r (which precedes t h e 70kA c o n d i t i o n i n time) i s w e l l i n e x c e s s of t h e measured v a l u e (615V). This i m p l i e s t h a t s i g n i f i c a n t n o z z l e a b l a t i o n a l s o o c c u r s a t 90kA although not photo- g r a p h i c a l l y d e t e c t e d .

The a x i a l v a r i a t i o n of e l e c t r i c a l f i e l d s t r e n g t h d e r i v e d from t h e V:z r e s u l t s shows a mon- o t o n i c d e c r e a s e f o r a l l c u r r e n t s i n both a i r and SF6 (Figs. 2 , 3 ) .

4 .

ACKNOWLEDG~AENTS

.

The a u t h o r s a r e g r a t e f u l t o F r o f e s s o r 2. G.

Craggs f o r h i s continued encouragement and t o t h e S c i e n c e Research Council f o r f i n a n c i a l s u p p o r t which enabled t h i s work t o be performed.

5 .

REFERENCES.

1 ) COYLEY M.D. J.Phys.D. Appl.Phys.,

2,

2218- 2231, 1974.

2 ) WALMSLEY H.L., JONES G.R., H A J I F., STRACHAN D.

J.Phys.D. Appl.Phys.,

2,

383-392, 1977.

3 ) AIREY D.R. Ph.D. T h e s i s , U n i v e r s i t y of Bath, 1977.

4 ) LIEBERMANN R.W. and CHAN C.L. Westinghouse Report 77-1C64-ARC PL

-

P j , May 31, 1977.

5 ) YOS J . M . AVCO Report, RAD-TM-63-7, 1967.

6 ) SHAYLER P.J. and FANG M.T.C. U n i v e r s i t y o f Liverpool, Arc Hes. Rept., ULAP-T45, 1976.

I t i s ( pulb lam1

F i g .