The following characteristics should help to ensure accuracy
as well as ease of interpretation:
a)
Keep it simple. A fundamental single-line
diagram should be made up of short, straight lines and components, similar to
the manner in which a block diagram is drawn. It should be relatively easy to
get the overall picture of the whole electrical system.
All, or as much as possible, of the system should be kept to
one sheet. If the system is very large, and more than one sheet is necessary,
then the break should be made at voltage levels or at distribution centers.
b)
Maintain relative geographic relations. In many
cases, it is possible to superimpose a form of the one-line diagram onto the
facility plot plan. This is very helpful toward a quick understanding of the
location of the system's major components for operating purposes.
It may, however, be more difficult to comprehend the overall
system operation from this drawing. Such a drawing could be used for relatively
simple systems. For more complex systems, however, it should be used in
addition to the fundamental single-line diagram.
c)
Maintain the approximate relative positions of
components when producing the single-line diagram. The drawing should be as
simple as possible and should be laid out in the same relationship as an
operator would view the equipment. The diagram does not need to show
geographical relationships at the expense of simplicity.
NOTE: A site plan with equipment locations may be required
to accompany the single-line diagram.
d)
Avoid duplication. Each symbol, figure, and
letter has a definite meaning. The reader should be able to interpret each
without any confusion. In this regard, equipment names should be selected
before publishing the document; then, these names should be used consistently.
e)
Show all known factors. All details shown on the
diagram are important. Some of those important details are as follows:
Manufacturers'
type designations and ratings of apparatus;
Ratios of
current and potential transformers and taps to be used on multi-ratio
transformers;
Connections
of power transformer windings;
Circuit
breaker ratings in volts, amperes, and short-circuit interrupting rating;
Switch and
fuse ratings in volts, amperes, and short-circuit interrupting rating;
Function of
relays. Device functions used should be from IEEE Std C37.2-1991;
Ratings of
motors, generators, and power transformers;
Number,
size, and type of conductors;
Voltage,
phases, frequency, and phase rotation of all incoming circuits.
The type of supply system (wye
or delta, grounded or ungrounded) and the available short-circuit currents
should be indicated.
f)
Future plans. When future plans are known, they
should be shown on the diagram or explained by notes.
g)
Other considerations. Refer to IEEE Std 141-1993
for further discussion of single line diagrams.
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