GE SBC23A Instructions Manual page 6

In t h e app l i ca t i on o f t h e S B C rel ays, probabl y t h e mo st i mpo rtan t c ons i de ra t i on i s
the s e tt i ng o f t h e ma i n t i me r.
t h e i n s tant the fau l t occ u r s unt i l t h e backup c i rcu i t breake r s ope ra te to c l ea r the
fau l t. Th i s to ta l
s tabi l i ty and to l i mi t a s much a s po s s i bl e t h e dama ge to t h e fa u l ted e qu i pment.
t h e o t h e r h and, i t m u s t be l ong eno u g h to pe rm i t t h e pr i ma ry re l ay i ng a nd pri ma ry
breake r to opera te and cl ea r t h e fa u l t, w i th ma r g i n.
prac t i ce to set the S B C t i m e r s o t h a t the o v e ra l l t i me of ope ra t i on ( i ncl u d i ng t h e
p i ckup t i me o f the c u r rent de tec tor and t h e ope ra t i ng t i me o f t h e B FT o u tpu t rel ay )
pro v i des fo r ampl e ma r g i n wi t h o u t i nfr i ng i ng on s tabi l i ty l i mi t i n t h e e vent o f a
breaker fa i l u re.
ma r g i n.
It i s appa rent from F i g u re 9 t h a t fo r any g i ven to ta l ope ra t i ng t i me o f the S B C,
red u c i n g t h e d ropo u t t i me o f the c u r rent de tec tor w i l l i nc rea s e t h e ma r g i n.
i s recommend ed, for appl i c a t i ons w h e re
c on templ a ted, that d ropo u t t i mes be reduced by reduc i n g t h e s e t t i n g o f t h e fi l l - i n
t i me r o f the c u r rent d etec to r.
w i t h t h e acceptabl e m i n i mum pi ckup o f the c u r ren t de tec tor.
The p i ckup o f t h e cu rrent d etec to r s ho u l d b e s e t fo r 6 7 % o r l e s s o f t h e m i n i mum
fau l t c u r rent fo r w h i c h the breake r - fa i l u re protec t i on mu s t ope ra te.
rec o gn i zed that the func t i on o f the c u r rent d e tecto r is to e s tabl i s h whe t h e r or no t
c u r rent i s fl owi ng i n the a s soc i a ted c i rcu i t b reake r.
sens i t i ve s e t t i ng i s d e s i rabl e.
d e t ec to r i s p i cked up on l oad, the s ec u r i ty of the s c heme i s re duced, s i nc e any
e rro r i n te s t i ng t h a t appl i ed DC to t h e re l ay c o u l d res u l t i n an und e s i red tr i p.
Th i s s ubjec t i s d i s c u ssed i n a l a t e r pa ra g raph d es c r i b i ng the u s e s o f t h e i so l a ted
conta c t ope ra ted from the o u tpu t of the l evel d etec to r.
Ano t he r fac tor i n t h e s e l ect i on o f a p i ckup s e t t i n g for t h e c u r rent de tec to r i s the
type o f c i rc u i t breake r i nvol v ed.
c i rc u i t when cl e a r i ng
s i gn i fi c ant t i me, and may h ave a substant i a l ma gn i tu d e.
c u r rent and i ts d u ra t i on mu s t be cons i d e red when de term i n i ng t h e s e tt i ng s o f t h e
l evel detector and ma i n t i me r i n t h e S B C.
re s i s to r c u r rent,
i nte rrupted, and
l onger. I f, on the o t h e r h and, the l ev e l de tec tor s e tt i ng i s above t h e res i s to r
c u r rent, i t w i l l re s e t w h en t h e ma i n bre ake r conta c t s open, t h e reby pe rm i t t i n g a
s h o rter t i me s e tt i ng on t h e ma i n S B C t i mer.
The non- i s ol a ted IT 2 conta c t o u tpu t o f the IT un i t i n t h e SB C23A, wh i c h connec t s to
s tud 9, i s i ntended
connec t i on d i a g ram in F i g u re 2 .
a dd i t i onal s ec u r i ty a g a i n s t s e a l - i n opera t i ons re s u l t i ng from s u c h c a u s e s a s s u rg e s,
e tc. The pu rpo se o f s u c h a func t i on i s to r i d e o v e r contac t bo unc e i n t h e 6 2 X
con tac ts ( i f s u c h bounc e ex i s ts ) and t o ma i nta i n t h e D C i np u t t o t h e SB C i n t h e
event o f a ze ro - vol ta ge fau l t t h a t coul d re s u l t i n r e s e t t i n g o f t h e i n i t i a t i ng
pro tec t i v e rel ays be fo re t h e SB C can t i me o u t.
adv i s ed l y, i na smu c h a s i t c an re d u c e t h e s e c u r i ty of t h e s c h eme d u r i n g te s t i ng i f
Fi g u re 9 i l l u s tra tes a l l t h e t i mes i nvol ved, from
t i me mu s t be s ho r t eno u g h to enabl e the sys tem to ma i nta i n
The IEEE Rel ay Commi ttee rec ommend s a t l ea s t th ree cyc l e s o f
The redu c t i on i n d ropo u t t i me mu s t be compa t i bl e
Howe v e r, i f t h e s e t t ings a re s u c h t h a t t h e c u r rent
Some c i rc u i t bre ake rs i ns e r t res i s to rs i nto t h e
a fau l t.
i t w i l l rema i n
h ence t h e ma i n S B C t i me r s e t t i n g mu s t be s e t propo r t i ona te l y
for u s e as a s e a l - i n func t i on,
T h i s s e a l - i n h as a s l i gh t t i me d el ay to prov i d e
GEK-45464
ma r g i ns o f l e s s
Th i s res i s to r c u r rent
If t h e l ev e l d etec to r i s s e t bel ow t h e
p i cked u p unt i l
Th i s
6
In g en e ra l , i t i s a good
t h an th ree cyc l e s
( Se e F i gu re 10. )
It s h o u l d be
In th i s s en s e,
i s ma i nta i ned
The v a l u e o f th i s re s i s to r
t h e re s i s to r c u r rent
a s s h own on t h e external
s e a l - i n s h o u l d
On
Thus i t
a re
th e mo s t
fo r a
i s
be used
-"