Table of Contents
Advertisement
The cho i ce betwee n very i nver s e and extreme l y i nver s e t i me re
1
i m i ted t h an between them and the i nver s e t i me re
i n t h e i r t i me-current character i s t i c curves .
i n verse t i me r e l ay s h ou l d be chosen as the t i me- current curves more near l y m atch the
fuse curve .
Another advan t age of the extreme l y i nver s e r e l ay i s t h at i t i s better
s u i ted than both the i nver s e and very i nver s e re l ays for pi c k i n g u p co l d l o ad .
a n y g i ven co l d l o ad pi ckup c apabi l i ty, the r e s u l t i ng sett i ngs wi l l provi d e f aster
pro tect i on at h i gh f au l t currents wi t h the extremel y i nver s e rel ay t h an wi th the
l es s i nvers e r e l ays .
The oper at i ng t i me of the t i me overcurrent u n i t for any g i ven val u e of current
and t ap sett i ng i s determ i ned by the t i me d i al sett i ng .
i nver se l y proport i on a l to the current magn i tu de as i l l u s tr ated by the t i me curves i n
F i g . 1 2, 13 and 1 4 .
mu l t i pl es of the tap sett i n g .
be the s ame for 80 amperes on the e i g h t ampere t ap as for 50 amperes on the f i ve
ampere t ap, s i nce i n both c ases, t h e current i s ten t i mes tap s ett i ng .
If s e l ecti ve act i on of two or more r e l ays i s requ i re d , determ i ne the m ax i mum
pos s i bl e short-c i rcu i t current of the
re l ay that d i ffers suff i c i en t l y to i n sure the proper sequ e n ce i n the operat i on of
sever a l c i rcu i t bre akers .
each bre aker after t h e r e l ay cont acts c l os e .
The i n stantaneou s cup u n i t i s torqu e contro l l ed by the d i rect i on a l u n i t .
i t i s used f o r d i rect tr i ppi ng, i t wi l l o n l y be necess ary when determ i n i ng a sett i n g
to con s i der the maxi mum current t h at the i n stantaneous u n i t wi l l s e e f o r a f au l t at
the remote term i n a l .
shou l d be set wi th a mar g i n of at l e ast ten per cent above the m ax i mum current for a
remote f au l t n e g l ect i ng tran s i ent overre ach .
The Y 1 A re l ays contai n a H i - Sei sm i c i n s t antaneous overcurrent u n i t .
m ay be
s et
h i gh
d eterm i n i ng the sett i n g for t h i s u n i t when i t i s u s e d for d i rect tri ppi n g, i t wi l l
be neces s ary to con s i der the maxi mum extern al f au l t for f au l ts at e ach e n d of the
l i ne because the u n i t i s n on - d i rect i on a l .
margin above the maxi mum
overreach a s i l l u s t r ated i n F i g . 17 .
The red jumper l eads between studs 18 and 1 9 and 19 and 20 are l oc ated i n s i de
the c ase on the cr ad l e bl ock and may be removed to provi de exter n a l torque contro l
of the t i me overcurrent u n i t (TOC) and the i nstantaneous overcurrent u n i t ( IOC)
respe ct i ve l y .
If exter n a l torqu e con t r o l of e i ther or bot h u n i t s i s requ i red,
remove the red j umper l e ad assoc i ated wi th the u n i t (s ) to be contro l l ed , and connect
1
the extern a
control contacts betwee n the appropr i ate s t u d s .
w i l l s t i l l be torqu e contro l l ed by the d i rect i o n a l u n i t i n add i t i on t o the exter n a l
contro l .
G EK - 49849
Note t h at the current val ues on these curves are g i ve n as
That i s, for a g i ven t i me d i a l s ett i ng, the t i me wi l l
A l l owance mu s t be m ade for the t i me i nvo l ve d i n ope n i n g
The i n stantaneous cup u n i t h as l ow tran s i en t overre ach .
to prov i d e
d i rect tr i ppi n g for
external fault taking into
1
ay as they are more n ear
For grad i n g wi t h f u s e s , t he e xtreme l y
1
i ne and then choo s e a t i me val u e for e ach
he avy
The u n i t s hou l d be set wi t h a s u i t abl e
accou nt the effects of trans i en t
5
1
ays i s more
1
y a
The operat i n g t i me i s
Th i s u n i t
i nter n a l
f au l t s .
Note t h at the u n i t s
1
i ke
F o r
Whe n
It
In
Advertisement
Table of Contents
