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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