WHITE PAPER / TELECOM TECHNOLOGY
EVALUATING TELECOMMUNICATIONS
OPTIONS FOR POWER
DISTRIBUTION SYSTEMS
BY
Wayne Ahrens, Mike Mahoney,
PE, AND Thanh
V. Nguyen, PE
While telecommunications and information technology have long
been used to operate the bulk power transmission system, the need
for a more intelligent grid is pushing information technology deeper
into distribution systems. Telecommunications is the chief challenge in
making this happen. Utilities are meeting this challenge with advances in
technology, combined with good planning and engineering principles.
WHITE PAPER / EVALUATING TELECOMMUNICATIONS OPTIONS FOR POWER DISTRIBUTION SYSTEMS
Electric utilities have taken advantage of advances in
technology to operate the electric power grid more
reliably and efficiently. The introduction of
microprocessor-based relays with communication
ports for gathering data has been a major component
of these advances. Devices in substations are gathering
data and sending it to control centers, while data is
transported between substations for transmission
line fault protection. As these telecommunications
technologies have advanced, they are becoming
financially and technologically feasible to deploy in
distribution applications. These experiences in deploying
substation and transmission telecommunications
networks are applicable to distribution; however,
there are additional design elements to consider.
TRANSFORMING DISTRIBUTION
(DNP) application designed to poll 50 devices once
The distribution grid has traditionally consisted of
every four seconds has different requirements than
unmonitored equipment that acted independently of any
an application gathering synchrophasor data from
remote control. Technicians would conduct routine visual
phasor measurement units 60 times each second.
inspections and respond to trouble calls to restore
service. Regulatory pressures and transformative factors
The first major decision in network design begins with
like distributed generation and increased use of
choosing the physical infrastructure. The two
renewables have resulted in a growing need for a more
fundamental types are wired vs. wireless infrastructure.
intelligent distribution grid.
Each comes with its own challenges.
Most utilities are beginning to deploy telecommunications
Wired infrastructure today means fiber. Fiber optics
networks for distribution applications. These applications
offers both reliability and high capacity, but the cost can
include advanced metering infrastructure (AMI) and
be prohibitive. This is because a cable must be installed
restoration and protection systems to increase reliability
to each network node. Cables must be installed aerially
and reduce outages. Asset health monitoring — as has
on utility poles or buried underground, which is
been seen with transformers and circuit breakers in
expensive given the cost of materials and labor, and the
substations — also can be applied to distribution assets.
process often requires time-consuming easements and
These are a few examples of the applications that can be
other public and private permissions to install. Existing
enabled by distribution telecommunications networks.
poles are often used where available, but structural
analysis often dictates pole replacements to support the
INFRASTRUCTURE: BUILDING
STRENGTH, WITHIN LIMITS
Distribution planners and engineers are faced with many
new cable. Despite these challenges, if the application
requires very high bandwidth and reliability, there is no
equal to fiber optics.
design decisions when seeking to deploy a distribution
telecommunications system. The design team must
Most utilities would be hard-pressed to justify the
understand the requirements of the applications they
expense of deploying fiber-optic cable to all distribution
seek to support because these will drive design decisions.
assets. A well-designed wireless infrastructure can be
The nature of the applications will determine design
a suitable alternative. The growing demand for wireless
parameters like network availability, throughput and
networks in the distribution sector has driven more
latency. For example, a distributed network protocol
vendors to bring solutions to market. This increased
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WHITE PAPER / EVALUATING TELECOMMUNICATIONS OPTIONS FOR POWER DISTRIBUTION SYSTEMS
competition has made wireless networks more
POINT-TO-MULTIPOINT topologies build on the point-to-
affordable, but it has also introduced so many options
point concept, with the added efficiency of connecting
that the best solution can be difficult to identify.
multiple remote radios to a single base station radio. In a
After the design team has determined that wireless
point-to-point scheme, connecting four endpoints to a
central location requires at least eight radios; however,
using a point-to-multipoint topology, these connections
WIRELESS NETWORK
DEPLOYMENT OPTIONS
could require as few as five radios. Point-to-multipoint
schemes take a bit more planning because there is a
limit on the number of remote radios that can be
• Point-to-point vs. point-to-multipoint
vs. mesh
connected to a single base station. This limit is
• Licensed vs. unlicensed frequencies
and technologies
bandwidth requirements of the application.
determined by the vendor technology and the
MESH topologies extend the point-to-multipoint
functionality to all radios in the network. A point-tomultipoint network requires defined base station and
technology will be used, technologies are evaluated
remote roles for each radio; in a mesh, every radio
through a Request-for-Information process. This process
is capable of sending and receiving data from multiple
often results in a sales “feeding frenzy” as vendors
points in a store-and-forward fashion. This allows the
look to gain a foothold with their technologies. It is
mesh to grow throughout the field area in more of a
important for the design team to stay focused on the
coverage map approach to design rather than defining
applications and the resulting design parameters.
specific paths. Since the network can reroute traffic in
Topology and frequency spectrum are major factors
the event of a single radio failure, this approach can also
in selecting a technology to deliver the reliability,
improve reliability. But a mesh usually requires more
throughput and latency requirements of the applications.
radios to provide for these coverage areas due to the
use of omnidirectional low-gain antennas that limit the
There are three network topology types to choose from
reach of any single radio.
when designing a wireless communication system: pointto-point, point-to-multipoint, and mesh. Each topology
The choice between topologies is not necessarily
introduces pros and cons that determine how it would
mutually exclusive. These topologies can be combined
fit into the final design.
to create a hybrid network as shown in Figure 1.
Each topology will have its own design considerations,
POINT-TO-POINT networks establish a dedicated link
frequency spectrum and technology. A hybrid
between two devices. Because this link is not shared
approach can often provide overall lower cost,
between multiple resources, all of the bandwidth is
greater reliability and/or higher bandwidth than a
available to transport data between the two endpoints.
one-size-fits-all approach.
his can be an inefficient use of resources — at times
when no data is being transported between endpoints,
Radio frequency spectrum and licensing also
the link’s capacity is not utilized. This is why point-to-
represent major design decisions for a wireless
point links are most often used to backhaul bulk data
network. Both licensed and unlicensed spectrum
from many devices in a field area network to a central
can be used. Most licensed radio frequencies offer
repository like a control center. Licensed digital
the benefit of regulatory protection from interference.
microwave radio is commonly used for wireless
On the other hand, licensed frequencies have more
point-to-point backhauling.
regulations and limitations on how they can be used.
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WHITE PAPER / EVALUATING TELECOMMUNICATIONS OPTIONS FOR POWER DISTRIBUTION SYSTEMS
FIGURE 1. Combining network technologies can strengthen reliability and efficiency.
The Federal Communications Commission’s (FCC)
Where licensed frequencies are unavailable or cost-
allocation of licensable radio spectrum for use by electric
prohibitive, unlicensed or license-exempt frequencies
utilities is extremely depleted. Obtaining new spectrum
are the only option. These unlicensed frequencies are
for these purposes usually requires purchasing the
subject to interference from other operators, but
spectrum from the FCC through an auction, or leasing
generally offer greater bandwidth and flexibility than
the spectrum from another party that owns it. This makes
licensed frequencies. The unlicensed frequencies most
acquiring new licensed spectrum difficult and expensive,
commonly used in the U.S. are from the industrial,
and sometimes impossible.
scientific and medical (ISM) frequency band with
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WHITE PAPER / EVALUATING TELECOMMUNICATIONS OPTIONS FOR POWER DISTRIBUTION SYSTEMS
spectrum at 902-928 MHz, 2.4-2.5 GHz and 5.7-5.9 GHz.
outlying capacitor bank behind an obstruction, with no
Frequencies below 900 MHz can reach longer distances
direct path to the mesh network, so a repeater provides a
and do not necessarily require line-of-sight for functional
point-to-point connection into the mesh for the
radio path. These signals can penetrate some
capacitor bank.
obstructions, an advantage in urban and forested areas.
Lower frequencies generally offer lower channel capacity
Substation B is also connected to the Tower, which
than higher frequencies. Higher frequencies generally
provides a high capacity point-to-point microwave link
offer more bandwidth and higher data rates, but require
to connect other substations into the fiber WAN, and
line-of-sight and shorter paths.
could support a point-to-multipoint base station for field
area remote radios. In this example, the Tower is being
When evaluating radio technology, it is important to
used to provide microwave connectivity to Substation A
understand that the range, bandwidth and other
rather than extending fiber-optic cable across the river.
performance specifications stated by vendors are usually
based on tests conducted in a lab environment under
A point-to-multipoint base station at Substation A
ideal conditions. Every environment is different;
connects to the fiber-optic network over the microwave
understanding how the products will perform in the
link for backhauling data from capacitor banks and
real-world field environment is vital when planning
reclosers in the area. This topology is needed because
a network. This understanding is best obtained through
the devices do not have line-of-sight to each other due
design field testing.
to the abundance of trees in the area, thus making a
mesh network not feasible.
Leasing services from a public carrier is an option for
deploying a private wireless network. Procuring carrier
Leased LTE cellular service is used to communicate with
services can be accomplished fairly easily, but it is
distribution switches. The area is cost-prohibitive to reach
important to understand what data security, reliability
with the network established at Substation A and B.
and bandwidth guarantees will be provided by the carrier.
Carrier services have a lower capital cost of deployment,
but recurring monthly costs must be considered
along with the question of relying on a third party for
what could be considered mission-critical services.
USE CASE: WIRELESS NETWORK
How do all these design decisions about topology,
technology and frequency translate to the real world?
Figure 1 illustrates an example of a telecommunications
segment for a distribution management system (DMS).
The DMS connects to the region over fiber to Substation
B, receives information and issues controls to optimize
the grid through applications at each connected node.
These applications could vary and include capacitor
banks, reclosers, sectionalizing, line sensors and regulators.
Substation B is connected by fiber to the utility wide area
network (WAN) providing a backhaul access point for
distribution assets in the area. Substation B connects to a
mesh network covering an area where the majority of the
assets have line-of-sight to each other. There is one
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WHITE PAPER / EVALUATING TELECOMMUNICATIONS OPTIONS FOR POWER DISTRIBUTION SYSTEMS
BIOGRAPHIES
FACTORS TO CONSIDER
Consider these questions when
determining how to deploy a
communications system:
• Topology
-- Point-to-point
-- Point-to-multipoint
-- Mesh
• Operating frequency
• Physical terrain and obstructions
• Application requirements
-- Throughput
-- Availability
DESIGN: BALANCING RELIABILITY,
SIZE AND COST
WAYNE AHRENS works in the Transmission &
Distribution Group at Burns & McDonnell. He has
experience designing and managing large-scale network
deployments in urban and remote environments. These
deployments include fiber-optic systems, satellite
communications, IP and MPLS networks, digital fault
recorders, SCADA, and teleprotection.
MIKE MAHONEY, PE, is a senior telecom engineer in the
Transmission & Distribution Group at Burns & McDonnell.
He has worked on numerous projects involving electric
utility substation local and wide area network design,
field area radio networks, substation physical security
design and installation, and North American Electric
Reliability Corp. (NERC) Critical Infrastructure Protection
(CIP) compliance.
THANH V. NGUYEN, PE, is a senior telecom
engineer in the Transmission & Distribution Group
at Burns & McDonnell. His experience with electric
Electric utilities are measured by metrics that include
utilities includes land mobile radio design, automated
system average interruption duration index (SAIDI),
metering systems, cellular data networks and broadband
system average interruption frequency index (SAIFI)
wireless networks. He also has experience in substation
and customer average interruption frequency index
design, distribution automation and energy
(CAIFI). Utilities have made large investments in energy
management systems.
generation, transmission lines and substations, but
the distribution system is where the power reaches
the customer. Distribution automation provides the
opportunity to improve these metrics. Also, the advent
of distributed generation and renewables that require
two-way power flow will be a game changer in terms
of how distribution grids will be operated in the future.
With proper planning and design, telecommunications
can play a key role by enabling distribution automation,
improving the customer experience while keeping up
10606-ETC-0416
with the challenges of a changing distribution paradigm.
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