<s>
In	O
power	O
engineering	O
,	O
a	O
single-line	B-Application
diagram	I-Application
(	O
SLD	O
)	O
,	O
also	O
sometimes	O
called	O
one-line	B-Application
diagram	I-Application
,	O
is	O
a	O
simplest	O
symbolic	O
representation	O
of	O
an	O
electric	O
power	O
system	O
.	O
</s>
<s>
The	O
one-line	B-Application
diagram	I-Application
has	O
its	O
largest	O
application	O
in	O
power	O
flow	O
studies	O
.	O
</s>
<s>
Electrical	O
elements	O
such	O
as	O
circuit	O
breakers	O
,	O
transformers	B-Algorithm
,	O
capacitors	O
,	O
bus	O
bars	O
,	O
and	O
conductors	O
are	O
shown	O
by	O
standardized	O
schematic	O
symbols	O
.	O
</s>
<s>
It	O
is	O
a	O
form	O
of	O
block	B-Application
diagram	I-Application
graphically	O
depicting	O
the	O
paths	O
for	O
power	O
flow	O
between	O
entities	O
of	O
the	O
system	O
.	O
</s>
<s>
A	O
one-line	B-Application
diagram	I-Application
can	O
also	O
be	O
used	O
to	O
show	O
a	O
high	O
level	O
view	O
of	O
conduit	O
runs	O
for	O
a	O
PLC	O
control	O
system	O
.	O
</s>
<s>
The	O
lines	O
in	O
the	O
single-line	B-Application
diagram	I-Application
connect	O
nodes	O
–	O
points	O
in	O
the	O
system	O
that	O
are	O
"	O
electrically	O
distinct	O
"	O
(	O
i.e.	O
,	O
there	O
is	O
nonzero	O
electrical	O
impedance	O
between	O
them	O
)	O
.	O
</s>
<s>
A	O
steady-state	O
of	O
each	O
bus	O
can	O
be	O
characterized	O
by	O
its	O
voltage	O
phasor	B-Application
;	O
the	O
system	O
state	O
is	O
defined	O
by	O
a	O
vector	O
of	O
voltage	O
phasors	B-Application
for	O
all	O
the	O
buses	O
.	O
</s>
<s>
In	O
a	O
physical	O
system	O
the	O
state	O
is	O
calculated	O
through	O
power	O
system	O
state	O
estimation	O
,	O
since	O
the	O
end	O
of	O
the	O
20th	O
century	O
this	O
process	O
involves	O
direct	O
simultaneous	O
measurements	O
(	O
synchrophasor	O
)	O
using	O
the	O
phasor	B-Application
measurement	O
units	O
.	O
</s>
<s>
A	O
one-line	B-Application
diagram	I-Application
is	O
usually	O
used	O
along	O
with	O
other	O
notational	O
simplifications	O
,	O
such	O
as	O
the	O
per-unit	O
system	O
.	O
</s>
<s>
A	O
secondary	O
advantage	O
to	O
using	O
a	O
one-line	B-Application
diagram	I-Application
is	O
that	O
the	O
simpler	O
diagram	O
leaves	O
more	O
space	O
for	O
non-electrical	O
,	O
such	O
as	O
economic	O
,	O
information	O
to	O
be	O
included	O
.	O
</s>
<s>
When	O
using	O
the	O
method	O
of	O
symmetrical	O
components	O
,	O
separate	O
one-line	B-Application
diagrams	I-Application
are	O
made	O
for	O
each	O
of	O
the	O
positive	O
,	O
negative	O
and	O
zero-sequence	O
systems	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
general	O
a	O
generator	O
will	O
have	O
different	O
positive	O
and	O
negative	O
sequence	O
impedance	O
,	O
and	O
certain	O
transformer	B-Algorithm
winding	O
connections	O
block	O
zero-sequence	O
currents	O
.	O
</s>
<s>
The	O
unbalanced	O
system	O
can	O
be	O
resolved	O
into	O
three	O
single	B-Application
line	I-Application
diagrams	I-Application
for	O
each	O
sequence	O
,	O
and	O
interconnected	O
to	O
show	O
how	O
the	O
unbalanced	O
components	O
add	O
in	O
each	O
part	O
of	O
the	O
system	O
.	O
</s>
