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Submitted on 1 Jan 1979
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MEASUREMENTS AT CURRENT ZERO IN A SF6 GAS BLAST BREAKER
R. Moll, E. Schade
To cite this version:
R. Moll, E. Schade. MEASUREMENTS AT CURRENT ZERO IN A SF6 GAS BLAST BREAKER.
Journal de Physique Colloques, 1979, 40 (C7), pp.C7-309-C7-310. �10.1051/jphyscol:19797152�. �jpa- 00219127�
JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment au n07, Tome 40, JuiZZet 1979, page C7- 309
MEASUREMENTS AT CURRENT ZERO IN A SF6 GAS BLAST BREAKER
R. Moll and E. Schade.
Brawn Boveri, Research Center CH-5405 Baden, BitzerZand.
INTRODUCTION
P o s t a r c c u r r e n t measurements a r e i m p o r t a n t f o r checking t h e range of v a l i d i t y o f a r c models which q u a n t i t a t i v e l y p r e d i c t t h e p o s t a r c c u r r e n t s i n h.v. b r e a k e r s according t o t h e r e s i d u a l c o n d u c t i v i t y
1
e.g. 1I .
I n t h e c a s e o f SF6 a x i a l l y blown a r c s however, such measurements p l a c e high demands on t h e measuring equipment because of t h e rap- i d recovery t h a t t a k e s g l a c e . To d a t e o n l y few measurements i n t h i s regime have been r e p o r t e d , and t h o s e were o b t a i n e d under v a r i o u s c o n d i t i o n s 12,3,41. I t has even been s t a t e d t h a t SF6 p o s t a r c c u r r e n t s can- n o t be d e t e c t e d . I n t h e f o l l o w i n g r e p o r t a measuring method i s d e s c r i b e d which d e t e c t sc u r r e n t s f a r below 1 A 1 5 ) . T e s t s a r e c a r - r i e d o u t w i t h t h i s measuring system ( r e - sponse time T~ < 35 n s ) on a m e t a l vapour- f r e e a x i a l l y blown SF6 a r c .
EXPERIMENTAL SETUP
The nozzle arrangement s e l e c t e d (Fig. 2 ) p e r m i t s u n r e s t r i c t e d o p t i c a l o b s e r v a t i o n s e x c e p t f o r t h e narrow o r i f i c e r e g i o n ( h i g h s p e e d - , s c h l i e r e n photography). The vapour produced by t h e upstream e l e c t r o d e i s drawn o f f through a s m a l l o r i f i c e i n t h e e l e c - t r o d e . A square-wave c u r r e n t p u l s e (1.5 kA, 5 m s ) followed by a decay r a t e of 30 ~ / y s i s g e n e r a t e d by an LC network 161. The a r c forms a s t a b l e plasma Column up-stream, while i t i s g r e a t l y i n f l u e n c e d by turbu- l e n c e downstream (Fig. 3 ) .
The recovery v o l t a g e i s s u p p l i e d by a h.v.
LC network ( F i g . 1 ) . The ' s p a r k gap F i s f i r e d approx. 25 ys b e f o r e t h e end of t h e 1.5 kA p u l s e ( c u r r e n t i n j e c t i o n , F i g . 5,7)
.
The RRRV i s determined by r e s i s t o r R2.
The p o s t a r c c u r r e n t i s determined from t h e v o l t a g e drop a c r o s s t h e 10 Q shunt RS,
which i s s h o r t c i r c u i t e d by t h e f a s t diode D b e f o r e c u r r e n t zero.
Network
1 I l l 1
Fig. 1: HS: vacuum b r e a k e r W : c u r r e n t t r a n s f o r m e r
T : r e s i s t o r / c a p a c i t o r d i v i d e r
T < 5 n s )
KO: bagtery-powered o s c i l l o s c o p e I n t h i s measuring arrangement s t r i c t ' c o a x - i a l d e s i g n o f a l l components must be pre- s e r v e d . Also t h e diode D c o n s i s t s of many c o a x i l l y arranged diodes. I n a d d i t i o n , t h e diode c h a r a c t e r i s t i c s should i n c l u d e a high maximum peak, forward s u r g e c u r r e n t , h i g h r e v e r s e v o l t a g e i n c a s e of a r e s t r i k e o f t h e t e s t s e c t i o n , low r e v e r s e c u r r e n t s , low j u n c t i o n c a p a c i t a n c e and a s h o r t recovery time. Since i t i s n o t p o s s i b l e t o o b t a i n a l l t h e s e requirements simultaneously, t h e most f a v o u r a b l e compromise must be s o u g h t , f o r each measuring t a s k . The response time
T~ of t h e p o s t a r c c u r r e n t measuring device i s l e s s t h a n 35 n s .
RESULTS AND DISCUSSION
The measuring s e t u p enabled p r e c i s e p o s t a r c c u r r e n t i n v e s t i g a t i o n s t o be performed.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797152
A g r e a t number o f t e s t s showed t h a t i n t h e c a s e o f i n t e r r u p t i o n measurable p o s t a r c c u r r e n t s ( F i g . 6 ) o c c u r o n l y under c o n d i - t i o n s l y i n g a t t h e l i m i t between e x t i n c t i o n and t h e r m a l r e i g n i t i o n . F i g . 4 shows a p o s t a r c . c u r r e n t measurement d u r i n g r e i g n i t i o n n e a r t h e c r i t i c a l c o n d i t i o n . The p o s t a r c c u r r e n t s measured a g r e e i m a m p l i t u d e and t e m p o r a l e v o l u t i o n w i t h t h e o r e t i c a l v a l u e s
111, a l t h o u g h i n t h e e x p e r i m e n t t h e c u r r e n t decay r a t e i s s e e n n o t t o have a s i n g l e c o n s t a n t v a l u e ( F i g . 5 , 7 ) . To a g r e a t e x t e n t t h e v o l t a g e r i s e (0.27 kV/ps) a t t h e c u r - r e n t z e r o i s l i n e a r . The e x t i n c t i o n l i m i t measured a g r e e s w i t h t h e t h e o r e t i c a l v a l u e s
11
I ,
when an a v e r a g e c u r r e n t decay r a t e (20 A/ps) i s assumed. The l i m i t e d o b s e r v a - t i o n o f p o s t a r c c u r r e n t s l e a d s u s t o be-F i g . 3 S c h l i e r e n r e c o r d R e i g n i t i o n
l i e v e t h a t i n s u l a t i n g l a y e r s a r e encoun- t e r e d which must b e broken down, and t h a t t h i s i s o n l y p o s s i b l e i n t h e v i c i n i t y o f t h e e x t i n c t i o n l i m i t and o f t e n l e a d s t o r e - i g n i t i o n . I n v e s t i g a t i o n s w i t h o t h e r n e t - works c o n f i r m t h i s a s s u m p t i o n , b u t t h i s phenomenon s h o u l d n o t a f f e c t t h e e x t i n c - t i o n l i m i t .
11
I
Hermann W . , R a g a l l e r K . , I E E E PAS-96 1546-1555 (1977) 121
F r i n d G . , IEEE Conference PaperNO. F 79 288-2 (1979)
131 Kobayashi A . , e t a l . IEEE PAS-97 1304-1312 (1978)
141 Murano M . , e t a l . I E E E PAS-94 1890-1900 (1975)
15 1 Moll R.
,
Schade E . , ISH, Milan 1979 161 Hermann W . , e t a l . IEEE PAS-951165-1176 (1976)
m e t a l v a p o u r e l e c t r o d e , ( t u n g s t e n ) SF6 3 - 4 b a r
1- 'U
nO"le; ( T e f l o n )1 bar
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e l e c t r o d e ( t u n g s t e n )
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10 mrnF i g . 2 T e s t b r e a k e r I n t e r r u n t i o n