IEEE Power & Energy Magazine - March/April 2017 - 46

Secondary Network
Electric utilities provide most electrical power to consumers
using radial distribution systems, as illustrated in Figure S1;
however, hundreds of secondary network distribution systems (networks) serve downtown business districts and other
dense-load or critical-load areas. Figure S2 illustrates the design of a secondary network distribution system, which is far
more complex and expensive than a radial distribution system.
Utility customers served by a network are supplied by ei-

New York City has one of the largest arrays of secondary networks in the world, with a high percentage of the footprints in
Brooklyn and Queens served by secondary networks. Secondary
networks are very different from radial distribution systems because
they are designed to supply loads having two or more distribution
feeders, with the secondaries tied together via multiple paths for
reliability and electric power capacity. To maintain reliability, network transformers tie in to the secondaries via a device known as a

ther a spot network or an area network (also known as grid
networks or street networks). Spot networks, illustrated in FigUtility Substation

ure S3, typically serve a single building or a section of a large
building and supply power at the 277/480-V level. Area networks, illustrated in Figure S2, cover a larger area; they often
serve hundreds or even thousands of customers, and they supply power at the 120/208-V level.

Example Radial Distribution
System Design (with Loop)

Feeder 2

Feeder 1

Utility Substation

Note: Any transformer/
customer load can be
served by either feeder
depending on the switch
positions.

Legend
Transformer
Closed Switch
Open Switch
Secondary
Circuit
Primary Feeder
Customer Load
Substation
Breaker

figure S1. An example of a radial distribution system.
(Image courtesy of NREL.)

load representations, harmonics and power-quality analysis, and a variety of supplementary areas that contribute to
the distribution planning process.
As these important distribution design tools become
more complex, they will require significant investments
in training and time, both of which are in short supply at
most any utility. Asking EDP engineers to absorb these
new methods and capabilities-in addition to performing their day-to-day job-is challenging and will require
46

ieee power & energy magazine

M

Example
Area Network
Distribution System

Customer
Site
Legend
Three-Phase
M Utility Meter
Network Transformer

Fuse

Network Protector
Primary Feeder

Breaker

Secondary Grid
Customer Load

Substation
Breaker

figure S2. An example of an area secondary network
distribution system. (Image courtesy of NREL.)

higher-level interfaces to help translate the engineering
outcomes into actionable plans.
An example of this is the National Rural Electric Cooperative Association's Open Modeling Framework (OMF),
which is based on open-source tools and openly available.
The OMF separates the user from the engineering analysis
by automating much of the modeling and simulation process and then layers a cost-benefit form over the engineering analysis. This allows the EDP engineer to compare how
march/april 2017



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2017

IEEE Power & Energy Magazine - March/April 2017 - Cover1
IEEE Power & Energy Magazine - March/April 2017 - Cover2
IEEE Power & Energy Magazine - March/April 2017 - 1
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IEEE Power & Energy Magazine - March/April 2017 - Cover3
IEEE Power & Energy Magazine - March/April 2017 - Cover4
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