IEEE
Std 493-2007
CHAPTER 4
Finally, the available standby capacity on each source that the utility is willing to dedicate
to the facility should be investigated. It is common for utilities to use multiple interties to
permit distribution feeders to back one another up. A feeder that has adequate capacity to
carry the entire facility load under normal conditions may not have that capacity available
if there have been multiple feeder outages and it is being used to back up other feeders.
4.4 Configuration
4.4.1 Where to begin—One-line diagram
The “blueprint” for electrical analysis is the one-line diagram. The existence of an up-todate one-line diagram is essential for any plant electrical engineer, manager, or operator. It
is the “road map” of the electric system. In fact, a current one-line diagram should exist
(or be prepared) even if the ensuing analysis is not done.
The one-line diagram should begin at the incoming power supply. Standard IEEE symbols
should be used in representing electrical components (see IEEE Std 315™).2 It is usually
impractical to show all circuits in a plant on a single schematic, so the initial one-line
diagram should show only major components, circuits, and panels. More detailed analysis
may be required in critical areas, and additional one-line diagrams should be prepared for
these areas as required.
Since an analysis is being made from the one-line diagram, the type, size, and rating of
each device as well as its availability should be shown on the diagram. The diagram
should include at least the following information:
a)
Incoming utility service: voltage, capacity and rating basis
b)
On-site generators
c)
Incoming main fuses, potheads, cutouts, switches, and main and tie breakers
d)
Power transformers: rating, winding connection, and grounding means
e)
Feeder breakers and fused switches
f)
Relays: function, use, and type
g)
Potential transformers: size, type, and ratio
h)
Current transformers: size, type, and ratio
i)
Control transformers
j)
All main cable and wire runs with their associated isolating switches, splices, and
terminations including length of run
k)
All substations, including integral relays and main panels, and the exact nature of
the load on each feeder and on each substation
If numerical reliability analysis is anticipated, the individual components defined in
Chapter 3 should be identified and the one-line diagram should represent, to the greatest
extent practical, the physical as well as electrical connections within the system. For
2Information
94
on references can be found in 4.10.
Copyright © 2007 IEEE. All rights reserved.
Authorized licensed use limited to: Nanyang Technological University. Downloaded on December 25, 2008 at 06:45 from IEEE Xplore. Restrictions apply.