G E K-49861
APPENDIX II
In the event that the SLY8l ope r a t i ng t ime i s de s i r e d f o r a
spec i f i c f au l t locat ion, the average ope r a t i ng t ime can be obt a i ned
f rom
F i g u r e 28 .
The ope r a t i ng
t ime can be obt a i ned
f rom
the
approp r i a t e c u r ve by c a l cu l a t i ng the equ i va l e n t vol tage appl i ed t o
t h e ope r a t i ng c i r cu i t b y means of t h e formu l a ( IA - Is ) ( ZRl - T Z I F ) ·
The r e lay i nco r po r a t e s a f i l t e r delay for fau l t s nea r the ba l a n c e
po i n t to p r e c l ude ove r r each o n CCVT t r a n s i e n t s .
Hence, the p r e f a u l t
e n e r g y i n the f i l t e r wi l l i n f luence the ope r a t i ng t ime on l i g h t e r
f a u l t s .
The uppe r curve i s appropr i a t e f o r r e s t r a i n t s e t t i ng s o f 4 0 %
o r h i gher, the m i ddle cu r ve for 2 0 % r e s t r a i n t s e t t i ng, and the low e r
c u r ve
for
1 0 % r e s t r a i n t
s e t t i ng .
Speed for
r e s t r a i n t
s e t t i ng s
b e t w e e n
1 0 %
a nd
2 0 %,
and
2 0 %
and
4 0 %
c a n b e
e s t i m a t e d
b y
i nt e rpol a t ion .
The da ta i s plot t ed for the fol low i ng cond i t ions;
( a ) Integ r a t i ng t ime r s e t for 5 . 5, 4 . 2/5 m i l l i s econd s ( 5 0 he r t z -
6 . 6, 5/6 m i l l i seconds )
( b ) No load i n the r e lay pr ior to the f au l t
( c ) The sou r ce and fau l t impedance have approx ima t e l y t h e s ame
impedance angle a s the r e l ay max imum r each .
Heavy p r e- f au l t load f low i n the r e lay can r e s u l t i n much s ho r t e r
ope r a t i ng t imes for clos e - i n fau l t s, and hence t h e s e c u r v e s s hou l d
not b e u s ed t o e s tabl i sh a m i n imum ope r a t i ng t ime .
Exampl e
As s ume t h e ope r a t e t ime i s des i r ed for a f au l t o n t h e l i ne s hown
be low for the f i r s t and second zone r e l ays at the l e f t end .
Th i s
examp l e i l l u s t r a t e s calculat ions for fau l t s i n the m i d d l e o f t h e l i ne
and a t the two ends .
The ope r a t i ng t imes are app rop r i a t e f o r one
pha s e - to-pha se measu
r
e
m
e
nt uni t for pha se- to-pha s e, pha s e - to-pha s e
to-g r ou nd, a n d t h r ee phas e fau l t s .
Howev e r, t h e ope r a t i ng t ime o n
t h r e e pha s e f au l t s w i l l b e s l i g h t l y f a s t e r than f o r the o t h e r t wo
t ype s, s i nc e a l l t h r ee u n i t s a r e ope r a t i ng, and the speed w i l l be
de t e r m i ned by the f a s t e s t mea s u r ement un i t of the t h r ee .
32
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