GE SBC23A Instructions Manual page 13

As wi l l be noted from Fi gu re 18, the i nput to the l ev e l - s en s i n g ci rcu i t i s pro v i ded
wi th four tra nsacto r c i rcuits.
propo rti o n a l to the respecti ve cur rent i nputs.
i nd i v i dual l y recti fi e d a nd the p h a s e c i rcu i t s a re sepa rated from th e g roun d ( 3Io )
ci rcui t. A porti on o f each o f the two ci rcui ts i s suppl i ed to the l ev e l - s en s i n g
ci rcu i t v i a potenti omete rs.
fi xed by des i gn,
i nd ependentl y, by mea n s of th e two pote nti omete rs i n conjuncti on w i th the current
tap sel ecti on. Note th at, s i nce the outputs o f a l l th ree p h a s e br i d ge rect i fi e r
ci rcu i t s a re i n paral l e l , the l evel d etecto r re spo nds to th e h i g h est o f t h e thre e
phase cur rents.
Fo r a phase -to-phase or p h a s e -to - g round faul t o r a s i n g l e -phase te st s i mul ati on, the
vol ta ge app l i ed to the i nput of the l ev e l - s en s i n g ci rcui t wi l l
recti fi ed s i g nal .
s i n e -wave curve, and then d rops o ff o n a s i ne-wave curve to zero ma gn i tude.
repeated a s l o n g a s the cur re nt i nput co nd i ti ons exi st.
output of the l ev e l - s en s i n g ci rcu i t cannot be co nti nuous u n d e r the s e co nd i t i on s
s i nce i t w i l l , re ga rdl e s s o f th e ma gn i tude o f th e i nput, d rop out tw i ce each cycl e,
every t i me the rect i fi ed output approaches and pa s s e s through zero.
reason that the fi l l - i n t i me r i s empl oyed to 11 r i d e o v e r 1 1 these gaps i n output from
the l ev e l - s en s i n g ci rcu i t.
magn i tud e o f the
adjustment, a s g i v e n i n the s ecti o n o n
fi l l - i n ti mer w i l l be set fo r someth i n g l o n g e r than a h a l f cycl e d ropout, so that a
conti nuous output from th i s t i mer w i l l be obta i ned when the peak v a l ue o f the i nput
s i gnal to the l evel - s e n s i n g ci rcu i t
ci rcu i t. Th i s i s the norma l factory setti n g of the fi l l - i n t i mer, a nd i t re sul ts i n
a 1 1d ropo ut 1 1 ti me o f the cur rent d etecto r that i s about 10 m i l l i seconds.
18.) The d ropout t i me i s somewhat l on g e r than the fi l l - i n t i me because of the
sto re d ene rgy i n the ma g n et i c c i rcu i t s a fte r the cur re nt d i sappea r s.
As was noted above, the ma i n t i rne r s requi re conti nuous i nput fo r the durati on o f
the i r sett i n gs i n o rd e r to t i me out.
fi l l - i n t i mer. I f fa ste r o v e ra l l d ropout t i me o f the cur rent detecto r i s requi red,
it i s n ece s s a ry to reduce the fi l l - i n ti me r s etti n g.
t i me r setting a nd no oth e r chan ge, a h i g h e r i nput cu r rent into the cu r rent detecto r
ci rcu i t s w i l l be requi red i n o r d e r to produce a co nti nuous output from the fil l - i n
t i mer.
( Se e F i gure 10. )
d etecto r i s d e f i n e d a s the RMS s i ne-wave cur re nt appl i ed at the i nput o f the re l ay
that produce s a co nti nuous output from th i s detecto r fo r the g i v e n fi l l - i n t i me r
setti ng. I t s houl d b e reco gn i zed th at i n maki n g th e p i ckup setti n g, o n l y s i n gl e
p h a s e cur rent i nputs s houl d be us ed.
gaps so that the i nput to the l e v e l - s e n s i n g c i rcu i t neve r goes to ze ro ( s ee Fi gure
21) .
I n summati on, the n o rmal facto ry setti n g o n the fi l l - i n ti me r i s fo r approx i mate l y 9
m i l l i s eco nds. W i th th i s sett i n g, the d ropout t i me o f the cur rent detector wi l l be
about 10 m i l l i seco n d s.
s ecti on on
RATINGS.
set fo r a s h o rte r ti me, a nd t h i s i n e f fect ra i s e s the p i ckup of the re l ay.
rel ati o n s h i p i s i l l ustra ted i n Fi gure 10.
s i ne-wave curre nt requ i red to produce a conti nuous output from the curre nt detecto r.
The vol ta g e outputs
S i nce th e s e n s i t i v i ty of the l ev e l - s e n s i n g c i rcu i t i s
the pi ckup setti n gs
Th i s s i g n a l sta rts at ze ro magn i tude, bui l d s up to a max i mum on a
The amount o f fi l l - i n t i me requ i red wi l l depend on the
i nput to the l evel - s e n s i n g
It i s
The ra nge o f p i ckup adjustment w i l l be a s g i v e n und e r the
If fa ster d ropout t i mes a re d e s i red, the fi l l - i n t i me r must be
GEK-45464
The outputs o f the tra n s actors a re
fo r pha s e a nd
ci rcu i t.
i s ba sed on the a s s umpt i on that the
RATINGS,
i s just equal to th e s e n s i ti v i ty o f that
Thus, a co nti nuous output i s requ i red from the
Th ree-pha s e cur rent i nputs tend to fi l l i n the
P i ckup cur rent i s d e fi ned a s the RMS
13
from each tra nsacto r a re
g round cur rents a re
be a ful l -wave
It i s obv i ous th at the
It i s fo r th i s
The ra nge o f
( See F i gure
W i th th i s re duced fi l l - i n
made
Th i s i s
p i ckup
Th i s