OPTIhAL RESTORATION OF SUPPLY FOLLOWING A FAULT ON LARGE DISTRIBUTION
SYSTEhS
Susheela Devi,
1).P..Sen Gupta and Samuel Sargunaraj
1 . 0 ABSTRACT
__-__________
A c o m p u t e r a i d e d o p t i m a l method h a s
been d e v e l o p e d f o r t h e r e s t o r a t i o n
of
e l e c t r i c s u p p l y t o a r e a s i s o l a t e d from t h e
network f o l l o w i n g a f a u l t i n a d i s t r i b u t i o n
system.
A s e a r c h t e c h n i q u e is u s e d
where
by
appropriate
the
s e a r c h is guided
heuristics.
The optimum s o l u t i o n e n t a i l s
f i n d i n g t h e s t r a t e g y which i n v o l v e s t h e
o p e r a t i o n of minimum number of
switchgear
for
rerouting the supply
within
the
c o n s t r a i n t of s p e c i f i e d loading.
This is
an e s s e n t i a l requirement i n c o u n t r i e s l i k e
I n d i a where t h e c i r c u i t b r e a k e r s a r e a l m o s t
a l w a y s m a n u a l l y o p e r a t e d a n d a number o f
transformers and feeders operate c l o s e t o
their rated capacity.
I t pays t h e r e f o r e t o
a d o p t d i f f e r e n t s t r a t e g i e s a t peak l o a d a n d
o f f peak c o n d i t i o n s s i n c e t h e number o f
b r e a k e r o p e r a t i o n s is s o c r i t i c a l .
The
restoration
of
supply
to
i s o l a t e d s e c t i o n s involves t h e opening and
c l o s i n g of switchgear so t h a t t h e i s o l a t e d
s e c t i o n i s f e d from a n a l t e r n a t i v e r o u t e .
In
the process,
there should
be
no
o v e r l o a d i n g of b u s e s , t r a n s f o r m e r s a n d l i n e
sections.
While f i n d i n g a s e r i e s
of
c o n n e c t i o n s and d i s c o n n e c t i o n s of s e c t i o n s
t o r e s t o r e supply,
t h e r e may b e
many
a l t e r n a t i v e s o l u t i o n s and i t is necessary
to find the optimal route.
I n India, the present p r a c t i c e is
f o r t h e o p e r a t i n g p e r s o n n e l t o make t h e
d e c i s i o n o n how t o r e s t o r e s u p p l y .
While
making t h e d e c i s i o n , w e h a v e t o k e e p i n
mind t h e c o n f i g u r a t i o n o f t h e s y s t e m a t t h e
time o f t h e o u t a g e a n d a l s o e n s u r e t h a t
It
t h e r e is no overloading on t h e system.
is e v i d e n t t h a t experienced personnel a r e
r e q u i r e d who a r e t o t a l l y f a m i l i a r w i t h t h e
system.
Nowadays w i t h t h e l a r g e s i z e o f
t h e d i s t r i b u t i o n systems and with
the
c a b l e s b e i n g pushed t o t h e i r l i m i t due t o
It
h i g h demand, t h i s i s a f o r m i d a b l e t a s k .
c a n t h u s be s e e n t h a t a computer program
which d i s p l a y s f e a s i b l e s o l u t i o n s should be
a welcome a i d t o t h e o p e r a t i n g p e r s o n n e l .
D i f f e r e n t a p p r o a c h e s h a v e b e e n made
and s t r a t e g i e s proposed f o r t h e r e s t o r a t i o n
following a f a u l t .
These i n c l u d e c l a s s i c a l
optimization techniques,
k n o w l e d g e- b a s e d
systems
and s e a r c h
techniques.
The
o p t i m i z a t i o n t e c h n i q u e h a s been u s e d i n
r e f e r e n c e s [ l ] and [ 2 1 .
The l i n e c a p a c i t y
constraint
and
transformer
capacity
c o n s t r a i n t a r e taken i n t o account.
In [21,
the c o n s t r a i n t of permissible voltage drop
h a s a l s o been added.
From t h e r e s u l t s
r e p o r t e d by t h e a u t h o r s t h e
solutions
o b t a i n e d seem t o r e q u i r e a v e r y l a r g e
number o f s w i t c h g e a r o p e r a t i o n t o r e s t o r e
power s u p p l y . T h i s may n o t c r e a t e p r o b l e m s
where t h e s w i t c h i n g s y s t e m is a u t o m a t e d a n d
centrally controlled.
References [31, [41
and
I51
utilize
the
k n o w l e d g e- b a s e d
approach.
I n [ 3 1 , a set of 16 r u l e s a r e
u s e d c o d e d i n INTERLISP.
T h i s program h a s
o n l y been t r i e d f o r a very s m a l l system.
The number o f r u l e s h a v e t o b e i n c r e a s e d t o
a l a r g e e x t e n t t o c a t e r t o l a r g e systems.
I n [ 4 1 , a n e x p e r t s y s t e m i n P r o l o g h a s been
r e p o r t e d c o n t a i n i n g 180 r u l e s .
This has
b e e n e n h a n c e d t o 382 r u l e s a s r e p o r t e d i n
[5].'
The use o f e x p e r t s y s t e m s seems t o
demand t h e i n c o r p o r a t i o n o f a l a r g e number
of
r u l e s when t h e n e t w o r k
considered
r e p r e s e n t s even a s e c t i o n of Metropolitan
d i s t r i b u t i o n system.
I n [ 6 1 , a b i n a r y t r e e s e a r c h is u s e d
w h e r e e v e r y s w i t c h i s s e t t o 0 o r 1.
This
type of b l i n d s e a r c h is l i k e l y t o t a k e a
v e r y l o n g time f o r a l a r g e s y s t e m u n l e s s
t h e s e a r c h i s g u i d e d by some r u l e s a n d
heuristics.
The c r i t e r i a f o r f i n d i n g a n optimum
s o l u t i o n is very c r u c i a l .
Generally the
c r i t e r i o n adopted is t o t r a n s f e r t h e load
t o be f e d t o a f e e d e r w i t h a l a r g e r margin
so t h a t t h e r e i s a b a l a n c i n g o f t h e l o a d .
As
h a s been i n d i c a t e d e a r l i e r
manual
s w i t c h i n g is u s e d i n I n d i a a n d p r o b a b l y i n
most of
the developing countries.
The
information on which switchgear a r e t o be
o p e r a t e d i s c o m m u n i c a t e d t o t h e l i n e m e n who
have t o go p h y s i c a l l y t o t h e l o c a t i o n o f
the
switches
t o operate
them.
The
restoration
of
supply
becomes
more
c o m p l i c a t e d a n d time c o n s u m i n g i f a l a r g e
number
of
switching
operations
are
involved.
Hence, t h e s t r a t e g y o f minimum
number o f s w i t c h e s t o b e o p e r a t e d w i t h o u t
exceeding
c u r r e n t limits i s t h e
only
p r a c t i c a l s o l u t i o n t o t h e problem
and
acceptable
to t h e supply
authorities.
Several
feasible
solutions
involving
minimum o p e r a t i o n o f s w i t c h g e a r may e x i s t .
I f more t h a n o n e s o l u t i o n e x i s t s , t h e n t h e
one t h a t o f f e r s t h e l a r g e s t l o a d i n g margin
is t o b e p r e f e r r e d u n l e s s o t h e r i n t a n g i b l e
yet
compelling
factors
need
to
be
considered.
The p r o p o s e d method c a n b e b e s t
Z e s c r i b e d a s a knowledge b a s e d
guided
search
aiming
at
minimum
switching
:?ration
a n d minimum o v e r l o a d i n g .
An
:.;era11 g u i d i n g p r i n c i p l e o n t h e s e a r c h i s
::at
t h e system should be a s balanced a s
rsssible.
The t e c h n i q u e e s s e n t i a l l y i n v o l v e s
s e a r c h i n g a tree r e p r e s e n t i n g a l l
the
sslutions possible.
Search is a g e n e r a l
Froblem
solving strategy suitable
for
Froblems w h i c h h a v e n o d i r e c t t e c h n i q u e s .
:n u s i n g t h e s e a r c h t e c h n i q u e c e r t a i n s t e p s
snould be followed which n e c e s s i t a t e t h a t
:ne
p r o b l e m h a s t o be d e f i n e d p r e c i s e l y
:ncluding
t h e i n i t i a l and f i n a l states.
:he problem h a s t o b e a n a l y z e d a n d a s e t o f
r u l e s ( o r o p e r a t o r s ) have t o b e s p e c i f i e d
: O a c t on a s t a t e a n d c o n v e r t i t t o a n o t h e r
A s o l u t i o n i s f o u n d by moving from
state.
the i n i t i a l t o t h e f i n a l s t a t e through
:ntermediate
states using t h e operators
specified.
The o r d e r o f t r a v e r s a l o f t h e
t r e e is c r u c i a l . I f t h e c o n t r o l s t r a t e g y i s
right,
t h e s e a r c h w i l l b e more e f f e c t i v e
end t h e s o l u t i o n can be o b t a i n e d f a s t e r .
3epending on t h e o r d e r of t r a v e r s a l o f t h e
tree, b r e a d t h - f i r s t s e a r c h ,
depth- first
search and b e s t - f i r s t s e a r c h a r e p o s s i b l e .
Breadth- First Search:
I n t h i s procedure,
a l l nodes on one l e v e l of
t h e tree a r e
expanded b e f o r e e x a m i n i n g a n y o f t h e n o d e s
on t h e n e x t l e v e l .
T h i s t y p e o f s e a r c h is
guaranteed t o f i n d a s o l u t i o n i f i t exists
and a l s o t h e s o l u t i o n w i t h t h e s h o r t e s t
path.
But t h i s p r o c e d u r e w i l l r e q u i r e a
l o t of memory a n d time i f t h e s o l u t i o n l i e s
t o o d e e p down i n t h e t r e e . T h i s i s b e c a u s e
the
number o f n o d e s t o
be
examined
increases exponentially with the depth.
T h i s s t r a t e g y was t r i e d f i r s t a n d s i n c e t h e
number o f o p e r a t i o n s i n c r e a s e s w i t h t h e
p l y , t h i s s t r a t e g y indeed gave t h e s o l u t i o n
w i t h minimum o p e r a t i o n o f s w i t c h g e a r .
But
s i n c e t h e system considered is very l a r g e ,
i n a few cases t h e c o m p u t a t i o n time i s
h i g h . To a v o i d s u c h c a s e s , t h e t r e e h a s t o
be p r u n e d so t h a t p a t h s u n l i k e l y t o o f f e r a
solution a r e not explored a t a l l .
For t h i s
h e u r i s t i c s have t o be used.
-Depth- First Search:
I n t h i s procedure one
node i s e x p a n d e d f u l l y b e f o r e a n o t h e r node
is c o n s i d e r e d .
Using t h i s procedure, i t is
likely
t h a t a l o t o f time i s
spent
It
is a l s o
exploring unfruitful paths.
n e c e s s a r y t o l i m i t t h e d e p t h t o which a
node is e x p a n d e d .
solution
is f e a s i b l e i f
t h e r e is
no
o v e r l o a d i n g on any p a r t of t h e system.
If
any of t h e s o l u t i o n s a r e f e a s i b l e , t h e task
is done.
O t h e r w i s e t h e s e form p a r t i a l
solutions,
and o t h e r r o u t e s a r e found t o
r e l i e v e t h e overload.
T h i s can be done i n
two ways.
The f i r s t i s t o s p l i t t h e
i s o l a t e d s e c t i o n a n d f e e d them by u s i n g two
n o r m a l l y - o p e n s e c t i o n s . The s e c o n d i s t o
r e l i e v e t h e o v e r l o a d on t h e f e e d e r t o which
t h e l o a d h a s been t r a n s f e r r e d .
These form
n o d e s o f p a t h l e n g t h two.
T h i s procedure
is r e p e a t e d t i l l a f e a s i b l e s o l u t i o n i s
f o u n d . Once a f e a s i b l e s o l u t i o n i s f o u n d ,
it is necessary t o backtrack
through t h e
tree t o f i n d t h e complete sequence o f
operations.
In
the
best- f irst
search,
a l t e r n a t i v e s a t p a t h l e n g t h one a r e f i r s t
found.
I f t h e r e is no f e a s i b l e s o l u t i o n s
t h a n o n e o f t h e s e is c h o s e n f o r e x p a n s i o n
depending on which f e e d e r h a s
minimum
overload.
I f t h e r e is s t i l l no f e a s i b l e
s o l u t i o n , then a l l t h e unexpanded nodes o f
p a t h l e n g t h o n e a n d p a t h l e n g t h two a r e
considered,
a n d a node where minimum l o a d
needs t o be t r a n s f e r r e d is chosen f o r
expansion.
This process is r e p e a t e d till a
f e a s i b l e s o l u t i o n is f o u n d .
P r u n i n g of t h e
-_________--------__
Tree:
While b r e a d t h - f i r s t
s e a r c h seems t h e o b v i o u s s t r a t e g y t o u s e
f o r t h e c r i t e r i a o f minimum o p e r a t i o n o f
i t may b e
time- consuming,
switchgear,
e s p e c i a l l y f o r very l a r g e systems.
One
method o f r e d u c i n g t h e s e a r c h i s t o d i s c a r d
paths
which a r e u n l i k e l y t o o f f e r
a
A h e u r i s t i c function has t o be
solution.
used here.
T h e s e p a t h s a r e a n t i c i p a t e d by
u s i n g a s i m p l e r u l e . When t h e l o a d s ( CP )
in
t h e post- fault region has
to
be
transferred t o another feeder X,
if the
l a t t e r ( i . e . , X ) i s o v e r l o a d e d by a n amount
P d u e t o t h e t r a n s f e r a n d a S e c t i o n T from
XOhas t o b e t r a n s f e r r e d t o a t h i r d f e e d e r Y
t o prevent overloading of X ,
t h e n CP
(i.e.,
t h e sum o f t h e l o a d s o f s e c t i o n TT
must n o t be much l a r g e r t h a n Z P
In other
w o r d s a n y s e a r c h t h a t l e a d s t o kn e x c e s s i v e
accumulation of t h e l o a d s t o be t r a n s f e r r e d
=
should be a n t i c i p a t e d and abandoned.CP
a XP where a i s o f t h e o r d e r o f 2 o r 3T i s
permkssible.
.
I n o r d e r t o a s c e r t a i n t h e loading of
t h e transformers, buses and f e e d e r s a l o a d
f l o w h a s t o b e computed whenever a t r a n s f e r
of l o a d is proposed.
A simple dc l o a d flow
is found adequate f o r t h i s purpose, s i n c e
loading
on t h e s y s t e m i s o n l y
being
checked.
I n case voltage drop o r system
l o s s e s n e e d t o be c a l c u l a t e d a d c l o a d f l o w
is obviously inadequate.
Since in our case
f i n e r a s p e c t s such a s obeying
voltage
c o n s t r a i n t s and minimizing system l o s s e s
g i v e way t o t h e p r i m e r e q u i r e m e n t s o f
minimizing switching o p e r a t i o n s
without
overloading,
dc l o a d flow s e r v e s
the
necessary purpose.
I
_
_
B e s_-----_
t - F i r s t S e--_arch:
--_
I n t h i s procedure,
a
h e u r i s t i c f u n c t i o n is used a t each s t a g e t o
d e c i d e w h i c h node t o e x p a n d .
The p u r p o s e
of t h e h e u r i s t i c f u n c t i o n i s t o g u i d e t h e
s e a r c h p r o c e s s i n t h e most
profitable
d i r e c t i o n by s u g g e s t i n g w h i c h p a t h
to
follow
f i r s t when more t h a n
one
is
a v a i l a b l e . H e u r i s t i c s a r e formed by u s i n g
d o m a i n - s p e c i f i c knowledge.
~
The s e a r c h t e c h n i q u e f i n d s a s e r i e s
of c o n n e c t i o n a n d d i s c o n n e c t i o n o f s e c t i o n s
t o r e s t o r e s u p p l y . I t is f i r s t s e e n which
a r e t h e normally- open s e c t i o n s which can
feed
the isolated areas.
These
form
a l t e r n a t i v e s of p a t h l e n g t h one.
These
involve j u s t a single operation.
Each
a l t e r n a t i v e is t e s t e d f o r f e a s i b i l i t y .
A
I t i s e v i d e n t t h a t t h e peak l o a d o n
the
system
during a day
should
be
considered f o r the r e s t o r a t i o n procedure t o
ensure safety.
O v e r l o a d i n g may t h u s b e
avoided even i f
t h e c a b l e may n o t b e
repaired
i n time.
B u t i t may n o t a l w a y s
it
be e x p e d i e n t t o u s e t h e peak l o a d i f
l e a d s t o a l a r g e number o f
switching
operations.
For example,
if
the fault
o c c u r s l a t e a t n i g h t when t h e l o a d i n g i s
light
mainly
due t o f a n s
and
airc o n d i t i o n e r s , i t is c o n v e n i e n t t o r e s t o r e
t h e s u p p l y w i t h minimum o p e r a t i o n s .
It
is
not always very convenient t o c a r r y o u t
manual s w i t c h i n g o p e r a t i o n s i n t h e m i d d l e
o f t h e n i g h t . The s t u d y c a n b e c a r r i e d o u t
based on l i g h t l o a d .
I n case t h e f a u l t may
n o t be r e p a i r e d b e f o r e t h e a d v e n t o f peak
l o a d , a s t r a t e g y b a s e d o n t h e p e a k l o a d may
be f o l l o w e d d u r i n g e a r l y morning.
v a r i o u s c a t e g o r i e s . A t any p o i n t i n
t h e l o a d a t a l o a d p o i n t w i l l be
L p = Pc
where L
R e s t o r a t i o n of s u p p l y based on t h e
peak l o a d i s s a f e b u t p e s s i m i s t i c a n d w i t h
continued l o a d growth ( o f t e n g r e a t e r than
10% a n n u a l l y ) and t h e s u r p l u s c a p a c i t y o f
c a b l e s being reduced, a f e a s i b l e s o l u t i o n
may n o t b e o b t a i n e d .
I f a solution exists
t h e c o m p u t a t i o n may t a k e l o n g a n d s e v e r a l
s w i t c h i n g s may b e i n v o l v e d .
I n such cases,
i t may b e more p r a c t i c a l t o d e c i d e t h e l o a d
From t h e
d e p e n d i n g o n t h e time o f t h e d a y .
time a t w h i c h t h e f a u l t o c c u r s , a time
h o r i z o n c a n be c o n s i d e r e d depending on t h e
time r e q u i r e d t o d e t e c t a n d r e p a i r t h e
fault.
The l a r g e s t l o a d d u r i n g t h i s time
can be considered f o r t h e
restoration
procedure.
Once t h e a c t i o n h a s b e e n t a k e n
i t is e s s e n t i a l t h a t t h e c a b l e s h o u l d be
r e p a i r e d a s e a r l y a s p o s s i b l e and c e r t a i n l y
w i t h i n t h e s p e c i f i e d time p e r i o d .
* s * cp / cc
is t h e e s t i m a t e d
P point p
Pc i s t h e p e r u n i t
c t o which p o i n t
S
is t h e estimated
C
is t h e connected
e
Cc
time,
load a t load
load of category
p belongs
total system load
load a t point p
is t h e t o t a l connected l o a d of
category c.
A program f o r r e s t o r a t i o n of
supply
h a s b e e n w r i t t e n i n PASCAL r u n n i n g o n t h e
IBM-PC.
A
very
large
metropolitan
d i s t r i b u t i o n system h a s been used
for
t e s t i n g t h e program.
T h i s system c o n s i s t s
o f o v e r 2500 n o d e s a n d 1 2 0 f e e d e r s .
The
u s e of such a l a r g e system l e d t o problems
of memory s p a c e a n d c o n v e r g e n c e .
To t a c k l e
the
convergence
problem,
appropriate
h e u r i s t i c s had t o be used a s e x p l a i n e d
earlier.
F i g u r e 1 s h o w s a small p a r t o f
this
system.
8 f e e d e r s h a v e b e e n shown.
For a
f a u l t i n s e c t i o n 6288- 7149 o f f e e d e r 7 1 4 9 ,
F i g . 2 shows t h e s e a r c h tree t h a t h a s b e e n
Since the a c t u a l load a t every point
I n Fig. 2, l e v e l 1 corresponds t o
formed.
is n o t known,
i t has t o be estimated.
solutions with a single operation.
If all
Since a c c u r a t e e s t i m a t i o n of t h e l o a d a t
t h e s e s o l u t i o n s show o v e r l o a d i n g , t h e s e
e v e r y l o a d p o i n t i s n o t p o s s i b l e a n d is n o t
If
have t o b e e x p a n d e d t o form l e v e l 2.
n e c e s s a r y e i t h e r , a s i m p l e method o f l o a d
s t i l l no s o l u t i o n is found, l e v e l 2 is
e s t i m a t i o n i s recommended.
G i v e n below a r e
expanded t o g i v e l e v e l 3.
Whenever a
t h r e e methods t o e s t i m a t e l o a d .
f e a s i b l e s o l u t i o n is f o u n d , b a c k t r a c k i n g t o
t h e r o o t node y i e l d s t h e t o t a l s o l u t i o n .
A s one goes deeper i n t o t h e tree,
the
Ir e, s_t_o rvast ei o_n~ rp_r o_cte hd urr ee e _c a_nt Yb~e e ~r u-n- :~ u~s-The
~
~
~
~
ing
number
of
operations
of
switchgear
t h r e e t y p e s o f l o a d d e p e n d i n g o n t h e time
So b y e x p a n d i n g o n e l e v e l a t a
increases.
of t h e day.
These a r e t h e morning peak,
time,
it is p o s s i b l e t o achieve
the
t h e e v e n i n g peak a n d t h e o f f peak.
These
objective of finding a s o l u t i o n with t h e
v a l u e s f o r e v e r y l o a d p o i n t have t o be
minimum p o s s i b l e o p e r a t i o n o f s w i t c h g e a r .
available.
F i g u r e 3 shows t h e s o l u t i o n o b t a i n e d
Use o f d a i l y--_________l o a d c u r v e s : T h i s method
2.
a t peak l o a d .
A
f e a s i b l e s o l u t i o n was
__________-_-_r e q u i r e s t h e l o a d s t o be c l a s s e d i n t o
o b t a i n e d a t t h e 2 1 s t t r i a l a t l e v e l 3 . The
v a r i o u s c a t e g o r i e s l i k e commercial l o a d ,
s o l u t i o n s a r e p r i n t e d o u t one l e v e l a t a
r e s i d e n t i a l l o a d , heavy i n d u s t r i a l l o a d ,
time. A t e a c h l e v e l , t h e n o d e w i t h minimum
l i g h t i n d u s t r i a l l o a d , e t c . The number o f
is e x p a n d e d
first.
This
overloading
c a t e g o r i e s w i l l depend on t h e r e g i o n being
p r i n c i p l e i s followed a t e v e r y s t e p so t h a t
considered.
F o r i n s t a n c e , i n some r e g i o n ,
t h e f i r s t f e a s i b l e s o l u t i o n displayed is
i t may b e p o s s i b l e t o c l u b t o g e t h e r t h e
t h e optimal solution.
The f i g u r e s
in
commercial
and r e s i d e n t i a l load.
The
brackets i n Fig.
2 shows t h e o r d e r o f
typical daily load curves for the various
expansion o f t h e tree. A l l s o l u t i o n s a r e
c a t e g o r i e s n e e d t o b e s t o r e d . The l o a d a s
printed out, stopping a f t e r every three
a p e r c e n t o f t h e peak l o a d is s t o r e d f o r
s o l u t i o n s so t h a t t h e s o l u t i o n s can be
t h e 24 h o u r s o f t h e d a y f o r t h e v a r i o u s
v i e w e d o n t h e VDU.
A l l feasible solutions
categories.
Every l o a d i n t h e system h a s
a r e boxed i n a n d h i g h l i g h t e d u s i n g
a
t o be c l a s s i f i e d . A t a n y time o f t h e d a y ,
different colour.
Since the
operating
knowing t h e peak l o a d a t a n y p o i n t ,
the
p e r s o n n e l may n o t f i n d i t p o s s i b l e t o
a c t u a l load can be estimated.
T h i s method
i m p l e m e n t t h e o p t i m a l s o l u t i o n d u e t o some
is j u s t a n approximation b u t v e r y s i m p l e
practical consideration,
he selects t h e
a n d f a s t t o implement.
next b e s t o u t of t h e p o s s i b l e s t r a t e g i e s
displayed.
T r i a l 21 g i v e s t h e optimal
3.
F o r e c a s t i n g---_-------t h e t o t a l system
s o l u t i o n b u t t h e s e a r c h can be continued i f
-----____l o a d : P a s t
d a t a on t h e t o t a l system l o a d has t o be
more s o l u t i o n s a r e r e q u i r e d .
used f o r f o r e c a s t i n g t h e p r e s e n t system
load.
Any o f t h e a v a i l a b l e f o r e c a s t i n g
we
Figure
4 shows t h e r e s u l t s
techniques can be used. T h i s t o t a l system
o b t a i n e d a t 30% o f t h e peak l o a d .
I t may
l o a d which is e s t i m a t e d h a s t o be a l l o c a t e d
b e more p r a c t i c a l t o i m p l e m e n t a s o l u t i o n
t o t h e v a r i o u s c a t e g o r i e s . I t is t h e r e f o r e
such a s t h i s during the night.
I f the
r e q u i r e d t o have t y p i c a l g r a p h s on t h e
c a b l e is n o t r e p a i r e d before t h e advent of
percent of
t o t a l load f o r the various
t h e peak t h e n e x t day, i t is a s i m p l e
c a t e g o r i e s a t d i f f e r e n t times o f t h e d a y .
m a t t e r t o i m p l e m e n t t h e s o l u t i o n a s shown
T h i s w i l l e n a b l e one t o a l l o c a t e
the
i n F i g . 3 . The s o l u t i o n a t 3 0 % p e a k l o a d
e s t i m a t e d s y s t e m l o a d a t a n y time t o t h e
can a l s o be o b t a i n e d very f a s t .
p.
w
1897
4899
4513
0
3454
I
7
,
Branching node
+ B u l k load point
g)
x
S e c t ionalizing switches
Normally open
Normally closed
Note:- Single Line diagram
simplified for c l a r i t y
1
A7
I
M
M
Figure - 1
0 6
45 d8; : : 4 7 8 1 5 24236
A 4 2 9 9
6286
Faulted section
6 2 8 8 - 7149
(11
C 61 48- 8323
(7)
)6068-1879 D6068-1879 D6068 -1879 D 7193-5120
:6555-5606 C2921-8698 C4657-22288 C6148-8323
(21)
D7791-8101
C 6 9 72 -1 817
D - Disconnect
C Connect
-
(3 1
(2)
C 7196- 27196
(8)
D 5199-5197
C 6972-1817
(18)
D 1879 - 5607
(10)
(9)
D6362- 6364
C7196-27196
(19)
C6474-6601
D6362 - 6364
C6474 - 6601
\
D 3064- 5243
C 6555-5606 C 2921 -8698
Figure - 2
(111
(14)
(13)
D5247-6472 D9138-1993 D8378-5692 D9138-199:
C6555-5606 C7196-27196 C4509 -4934 C6148-832:
.3
\
(20)
(15)
D 5607 - 3067
C 4657- 22288
09521 - 4 9 4 7
C 2921 - 8 6 9 8
(16)
D5607-3067
C 4657-22208
(171
D5122-9498
C 6148-8323
FAULT AT 6288- 7149
T r i a l No. 1
C o n n e c t 7196 7 7 ' 9 6
No. o f o p e r a t i o n s : 1 .
3 v e r l o a d i n g o f f e e d e r : 50%
Solution unacceptable
___________
T r i a l No. 2
C o n n e c t 6148 8 3 2 3
No. o f o p e r a t i o n s : 1.
3verloading of feeder:
Solution unacceptable
63%
Z-LaL%:2
C o n n e c t 6474 6 6 0 1
No. o f o p e r a t i o n s : 1.
3verloading of feeder:
Solution unacceptable
50%
?riaL!o:A
Disconnect
6 0 6 8 1 8 7 9 C o n n e c t 6 5 5 5 5606
C o n n e c t 7196 27196
of o p e r a t i o n s : 3.
O v e r l o a d i n g o f f e e d e r : 29%
Solution unacceptable
No.
T r i a l No. 5
D i s c o n n e c t 6068 1879 Connect 2921 8698
C o n n e c t 7196 27196
No. o f o p e r a t i o n s : 3 .
O v e r l o a d i n g o f f e e d e r : 38%
Solution unacceptable
c a s e no f e a s i b l e s o l u t i o n s a r e a v a i l a b l e ,
l o a d s h e d d i n g may h a v e t o b e r e s o r t e d t o .
I n India and o t h e r developing c o u n t r i e s ,
f i n d i n g t h e l o c a t i o n of t h e f a u l t takes
very long s i n c e t h e personnel have t o go t o
t h e location o f
the lines to find the
fault.
D u r i n g t h i s time i f s o l u t i o n s f o r
s e v e r a l p o t e n t i a l f a u l t locations a r e found
and s t o r e d ,
t h e time t a k e n t o f i n d a
s o l u t i o n is n o t s o c r i t i c a l .
I t
is e v i d e n t t h a t w i t h growing
demand
it
will
become
increasingly
d i f f i c u l t t o f i n d s o l u t i o n s t o restore
supply i f
peak l o a d is u s e d f o r
the
computation.
Using peak l o a d o b v i o u s l y
g i v e s a s a f e s o l u t i o n which is v a l i d a t a l l
times o f
t h e day.
However,
the large
number o f m a n u a l o p e r a t i o n s t h a t may b e
of
required to e f f e c t the restoration
s u p p l y may b e d i f f i c u l t t o c a r r y o u t w i t h i n
a s h o r t time, e s p e c i a l l y d u r i n g t h e n i g h t .
The
strategy
of
restoring
supply
immediately, based on off- peak l o a d and
r e v e r t i n g t o t h e one based on peak l o a d ( i f
reduce
t h e s o l u t i o n i s d i f f e r e n t ) may
complaints
and e a s e pressure
or?
the
Use
p e r s o n n e l from t h e a f f e c t e d c u s t o m e r s .
of estimated l o a d f o r t h e
restoration
procedure
is p e r m i s s i b l e p r o v i d e d
the
c a b l e s may b e r e p a i r e d p r o m p t l y .
The
e s t i m a t i o n o f t h e l o a d c a n b e d o n e a s shown
i n t h i s paper.
This w i l l give f a s t e r
s o l u t i o n s w i t h lesser number o f
switchgear
t o be o p e r a t e d .
-___-__I
TriaL!o:-zo
Disconnect
5607 3067 C o n n e c t 4657 22288
D i s c o n n e c t 6 3 6 2 6364 C o n n e c t 7196 27196
C o n n e c t 6148 8 3 2 3
No. o f o p e r a t i o n s : 5 .
O v e r l o a d i n g o f f e e d e r : 45%
Solution unacceptable
2riaLNo:_21
D i s c o n n e c t 7791 8101 Connect 6972 1817
D i s c o n n e c t 7193 5120 Connect 6148 8323
C o n n e c t 7196 27196
No. o f o p e r a t i o n s : 5
Solution feasible.
Fig.
3 : S o l u t i o n s a t peak l o a d
FAULT AT 6288
-
7149
1
C o n n e c t 7196 27196
T r i a l No.
-----__-___
of operations:
Solution feasible
No.
T r i a l No. 3
C o n n e c t 6474 6 6 0 1
No. o f o p e r a t i o n s :
Solution feasible
F i g . 4:
A o k i , K. Nara, M. I t o h , T. S a t o h , H.
Kuwabara, ' A N e w A l g o r i t h m f o r S e r v i c e
Restoration
i n Distribution Systems',
IEEE T r a n s . o n Power D e l i v e r y , Vol.
4,
No. 3 , J u l y 1 9 8 9 .
K.
T.
S a k a g u c h i , K . Matsumoto,
'Development o f a Knowledge B a s e d S y s t e m s f o r
Power S y s t e m R e s t o r a t i o n ' , IEEE T r a n s .
PAS, Vol. PAS-22, No. 2 , F e b r u a r y 1 9 8 3 .
1
TridlL52:2
C o n n e c t 6148 8 3 2 3
No. o f o p e r a t i o n s :
Solution feasible
Aoki,
H . Kuwabara,
T.
Satoh,
M.
Kanezashi,
' O u t a g e S t a t e O p t i m a l Load
A l l o c a t i o n by A u t o m a t i c S e c t i o n a l i z i n g
Switches
Operation i n
Distribution
on
Power
Systems',
IEEE
Trans.
D e l i v e r y , Vol.PWRD-2,No.4,0ctober
1987.
K.
1
1
Chen- Ching L i u ,
S e u n g Jee Lee,
S.S.
V e n k a t a , 'An E x p e r t S y s t e m O p e r a t i o n a l
A i d f o r R e s t o r a t i o n a n d Loss R e d u c t i o n
of
D i s t r i b u t i o n S y s t e m s ' , IEEE T r a n s .
o n Power S y s t e m s , Vo1.3, No.2,May 1 9 8 8 .
S.J.
Lee, C . C . L i u , S.S. V e n k a t a ,
'An
Extended E x p e r t System f o r
Service
Restoration of D i s t r i b u t i o n Feeders',
Power
Systems,
IFAC
Symposium,
Modelling and Control
Applications,
September 1988.
'
S o l u t i o n s a t 3 0 % peak l o a d
Morelata,
A.
Monticelli,
'Heuristic
Search
Approach
to
D i s t r i b u t i o n System R e s t o r a t i o n ' ,
IEEE
Trans.
o n Power D e l i v e r y , Vol. 4 ,
No.
4 , October 1989.
A.L.
6.
CONCLUSION
The p a p e r d e s c r i b e s a m e t h o d f o r
r e s t o r a t i o n of
supply to a r e a s i s o l a t e d
from t h e s u p p l y on t h e o c c u r r e n c e o f a
f a u l t . The method is s i m p l e a n d e f f i c i e n t
and is s u i t a b l e f o r h a n d l i n g v e r y l a r g e
s y s t e m s . The c r i t e r i a u s e d f o r o p t i m a l i t y
is t h e minimum o p e r a t i o n o f s w i t c h g e a r .
In
( 7 1 S u s h e e l a D e v i , D.P. S e n G u p t a ,
Samuel
Sargunaraj,
'A Search Technique
for
Complex
Restoring
Power S y p p l y i n
D i s t r i b u t i o n S y s t e m s , V I NPSC, Bombay,
J u n e 4- 7, 1990.