Allis-Chalmers BWX-6637-5, Instruction Book

Page: 39 / 88

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ON I
S TAT I C O V E R C UR R E NT T R I P D E V I C E
A . I NTR ODUCT I ON T h e
A I
l i s - Cha l me r s S t a t i c O v e r cu r re n t
T
r i p
Dev i ces
a r e
s t a t i c ;
t h a t i s t h
e
r
e
a re
n o mov i ng pa r t s o r co n t a c t s . The
c i r c u i t s
of
t h e dev i ce a re des i gned f o r l i gh t l o a d i n g of componen t s and a n.,
t empe ra t u re c om pe ns a t e d f o r a c c u r a cy a n d s t a b i l i ty o f ca l i b r a t i on o
v
e r w i de
t empe r a t u r e
r a
n
g
e
s f o r i nd e f i n i t e p e r i od s
of
t i me . Th e s
t
a t i
c
ove r c u r ren t
t r
i p
dev i ces ,
wh i ch r e p l a c e t he e l ec t ro -mec h a n i c a l
s
e r i e s ove r cu r r e n t t r i p
d e v i c es ,
pe r f o rm t h e s ame f u nc t i on w i th
a
h i gh e r d e g r e e o f
a c c u r a c y
and
v e r s a t i. l i ty .
I n
c ommon w i t h s e r i e s · ove r c u r r e n t t r i p dev i ce s , a l l e n e r gy
f o r
ope ra t i on I s
o
b
t
a i ned f ran ov e r l oa d
o r
f a u l t c u r r en t .
No
b
a t
t
e
r i e
s
o r
o t h e r ex t e rna l p
ow
e r s ou r ces a r e requ i red .
T h e
comp l e t e s ta t i c ove r c u r re n t t r i p s y s t em
cons i s t s of
t h ree c u r r e n t t ra n s ­
f o rme r s , one p e r p h a s e , moun t e d on t h e c i r cu i t b re a k e r p r i ma r y c on n ec t o r s ,
a
r e l e a s e magne t , a n d t h e s t a t i c ove r c u r r e n t t r i p d ev i ce . T h i s s y s t em
ope r a t es to t r i p t h e c i r cu i t b r eake r wh en a s y s t em o v e r l oad cond i t i on exc e ed�
a
p re - s e l e c t ed va l ue of c u r ren t . T r i pp i ng w i l l
occ u r
a f te r a p r ed e t e rm i n e d
t i me de l ay o r i ns t a n t a neous l y dep
e
n d i n g upon t h e adj u s tmen t s e l e c t e d a nd t h e
ma g n i t ude of t h e ove r l oad .
The s ta t i c
t r i p
de
v i c e c o n t a i ns t h ree cu r r e n t t r an s f o rme r s wh i ch p r ov i de a
�ma l l
l ow vo l t a ge s econd a ry c u r ren t p r opor t i ona l t o t he c i r cu i t b r eake r
p r i ma ry c u r r en t . T h e s econd a r y o f e a ch t ra n s f o rme r i s c o
n
n e c t e d i n s e r i e s
w
i t
h
a
powe r s u pp l y t ra ns f o rme r
and a n a ux i 1
i a ry t r a ns f o rme r . Th e
ou t p u t
o f t h e
powe r s u pp l y t r an s f o rme r s i s r e c t i f i ed t o p ro v i de
D . C .
e n e r g y t o t he
re l ea s e
mu gne t t r i p co i l a n d a l s o a regu l a ted
D. C .
p owe r s upp l y
t
o ope ra t e
t r ans i s t o r c i rc u i t s . Po t e n t i ome t e:: r s
o r
r h eos ta t s con n e c t e d i n p a r a l l e l
w i th
the
a ux i l i a ry t ra n s f o rme r s p r ov i de a n
A . C .
s i gna l vo l t a ge p r opor t i ona l
to
t lt e p r i ma ry c u r re n t . Th i !> a c t s as
the
i n t e l l i gence
i np u t
for t he d ev i ce ,
and
t he
ma gn i t u d e o f t h i s A . C .
v o l t a ge
de t e rm i nes whe t h e r o r
n
o t
t he b r c a �c r
w i I I t
r
i
p a n d t he t i me de l ay be f o r e t r i pp i n g . The r e l a t i on be tween
t
h
i
s
A . C .
s. i g n .: d v o l t a ge a n d t h e p r i ma ry c u r r e n t c a n be va r i e d b y a d
j
us t i n g t h e
po t e n t i ome t e r � t o s e t the rn i n i mum p r i ma r y c u r r e n t a t wh i ch t r i pp i n g w i l l
o c c u r . T h i s i s
t
he
p i c k - u p a d j us tme n t .
A
t ra n
s
i s t o
r
t r i gge r c i r c u i t p reven t s ope ra t i on
of
t h e
t i m i n g c i r c u i t
u n l es s
t h e
s i g n a l
ex
c
e
ed
s
95%
of p i c k-up
v a l ue .
I f t h e t r i g g e r h a s ope r a t ed , a
c a p a c i to r w i l l cha r ge � ra d u a l l y
i o
a v o l t a ge wh i ch c a u s es t h e s t a t i c s w i t � h
t o o�e r a t e ,
ene r g i z e t he
t r i p c o i
1 , a n d
t r i p
t h e b r ea ke r .
I f a
t a n y t i me
be f o r e t h e s t a t i c sw i t ch
a c t u a l J y
ope
ra t
es
,
t h e p r i ma r y c u r r en t
d e c r ea s e s
to
9 5%
o r
l e s s o f
t he
s e t
p i c k - u p ,
t
h
e
t r i g g e r
w i 1 1 t u r n
o f f
i:lnd
r e s e t
\"' i 1 1 t u ke
p l c:. u � .
� 0111<:!
m i nu r v a r i a t i on s i n p i c k - up a n d t i me de l ay may be
expe
c t
e
d
w i t h t empe ra t u r e
f l u c t u a t i on s
f r om
a n amb i e n t o f
-4o°C .
t o an amb i en t
o f 5 5 °C .
A t y p
i
c
a
l
b reake r
r a t i n g p l a t e i s s hown
i n F
i g
u
r
e
7A.
The max i mum r a t ed
ampe res i s d e t e rm i ned b y
t he c u r ren t
t ra n s f o rme r s m o u n t e d on t
h e
c i rcu i t
b re a ke r
p r i ma ry connec t o r s .
The
max i mum
c
u
r
r
e
n
t
ava i l ab l e i s 1
i m i t e d b y
t he
c i r·c u i t b
r
e
a
l-.e
r f rame s i ze . S i nce t h e
s ta t i c
o v
e r
c u
r r
en
t
t r i p
d e
v
i
c
e
componen t!
a r e ca l i b r a t e d i n
t e rms o f
t r
a ns
f o r
m
e
r s econda ry c u r r en t , t h e s an.e dev i c e can
b€
u � e J w i th
a ny
of
t he
g r oups of c u r r e n t t r a
n
s
f o r m e r s
a
v
a i l
a
b l
e
.
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