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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

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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 DISTRIBUTIONThe distribution grid has traditionally consisted of

unmonitored equipment that acted independently of any

remote control. Technicians would conduct routine visual

inspections and respond to trouble calls to restore

service. Regulatory pressures and transformative factors

like distributed generation and increased use of

renewables have resulted in a growing need for a more

intelligent distribution grid.

Most utilities are beginning to deploy telecommunications

networks for distribution applications. These applications

include advanced metering infrastructure (AMI) and

restoration and protection systems to increase reliability

and reduce outages. Asset health monitoring — as has

been seen with transformers and circuit breakers in

substations — also can be applied to distribution assets.

These are a few examples of the applications that can be

enabled by distribution telecommunications networks.

INFRASTRUCTURE: BUILDING STRENGTH, WITHIN LIMITSDistribution planners and engineers are faced with many

design decisions when seeking to deploy a distribution

telecommunications system. The design team must

understand the requirements of the applications they

seek to support because these will drive design decisions.

The nature of the applications will determine design

parameters like network availability, throughput and

latency. For example, a distributed network protocol

(DNP) application designed to poll 50 devices once

every four seconds has different requirements than

an application gathering synchrophasor data from

phasor measurement units 60 times each second.

The first major decision in network design begins with

choosing the physical infrastructure. The two

fundamental types are wired vs. wireless infrastructure.

Each comes with its own challenges.

Wired infrastructure today means fiber. Fiber optics

offers both reliability and high capacity, but the cost can

be prohibitive. This is because a cable must be installed

to each network node. Cables must be installed aerially

on utility poles or buried underground, which is

expensive given the cost of materials and labor, and the

process often requires time-consuming easements and

other public and private permissions to install. Existing

poles are often used where available, but structural

analysis often dictates pole replacements to support the

new cable. Despite these challenges, if the application

requires very high bandwidth and reliability, there is no

equal to fiber optics.

Most utilities would be hard-pressed to justify the

expense of deploying fiber-optic cable to all distribution

assets. A well-designed wireless infrastructure can be

a suitable alternative. The growing demand for wireless

networks in the distribution sector has driven more

vendors to bring solutions to market. This increased


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competition has made wireless networks more

affordable, but it has also introduced so many options

that the best solution can be difficult to identify.

After the design team has determined that wireless

technology will be used, technologies are evaluated

through a Request-for-Information process. This process

often results in a sales “feeding frenzy” as vendors

look to gain a foothold with their technologies. It is

important for the design team to stay focused on the

applications and the resulting design parameters.

Topology and frequency spectrum are major factors

in selecting a technology to deliver the reliability,

throughput and latency requirements of the applications.

There are three network topology types to choose from

when designing a wireless communication system: point-

to-point, point-to-multipoint, and mesh. Each topology

introduces pros and cons that determine how it would

fit into the final design.

POINT-TO-POINT networks establish a dedicated link

between two devices. Because this link is not shared

between multiple resources, all of the bandwidth is

available to transport data between the two endpoints.

his can be an inefficient use of resources — at times

when no data is being transported between endpoints,

the link’s capacity is not utilized. This is why point-to-

point links are most often used to backhaul bulk data

from many devices in a field area network to a central

repository like a control center. Licensed digital

microwave radio is commonly used for wireless

point-to-point backhauling.

POINT-TO-MULTIPOINT topologies build on the point-to-

point concept, with the added efficiency of connecting

multiple remote radios to a single base station radio. In a

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

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

connected to a single base station. This limit is

determined by the vendor technology and the

bandwidth requirements of the application.

MESH topologies extend the point-to-multipoint

functionality to all radios in the network. A point-to-

multipoint network requires defined base station and

remote roles for each radio; in a mesh, every radio

is capable of sending and receiving data from multiple

points in a store-and-forward fashion. This allows the

mesh to grow throughout the field area in more of a

coverage map approach to design rather than defining

specific paths. Since the network can reroute traffic in

the event of a single radio failure, this approach can also

improve reliability. But a mesh usually requires more

radios to provide for these coverage areas due to the

use of omnidirectional low-gain antennas that limit the

reach of any single radio.

The choice between topologies is not necessarily

mutually exclusive. These topologies can be combined

to create a hybrid network as shown in Figure 1.

Each topology will have its own design considerations,

frequency spectrum and technology. A hybrid

approach can often provide overall lower cost,

greater reliability and/or higher bandwidth than a

one-size-fits-all approach.

Radio frequency spectrum and licensing also

represent major design decisions for a wireless

network. Both licensed and unlicensed spectrum

can be used. Most licensed radio frequencies offer

the benefit of regulatory protection from interference.

On the other hand, licensed frequencies have more

regulations and limitations on how they can be used.

WIRELESS NETWORK DEPLOYMENT OPTIONS• Point-to-point vs. point-to-multipoint

vs. mesh

• Licensed vs. unlicensed frequencies and technologies


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The Federal Communications Commission’s (FCC)

allocation of licensable radio spectrum for use by electric

utilities is extremely depleted. Obtaining new spectrum

for these purposes usually requires purchasing the

spectrum from the FCC through an auction, or leasing

the spectrum from another party that owns it. This makes

acquiring new licensed spectrum difficult and expensive,

and sometimes impossible.

Where licensed frequencies are unavailable or cost-

prohibitive, unlicensed or license-exempt frequencies

are the only option. These unlicensed frequencies are

subject to interference from other operators, but

generally offer greater bandwidth and flexibility than

licensed frequencies. The unlicensed frequencies most

commonly used in the U.S. are from the industrial,

scientific and medical (ISM) frequency band with

FIGURE 1. Combining network technologies can strengthen reliability and efficiency.


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outlying capacitor bank behind an obstruction, with no

direct path to the mesh network, so a repeater provides a

point-to-point connection into the mesh for the

capacitor bank.

Substation B is also connected to the Tower, which

provides a high capacity point-to-point microwave link

to connect other substations into the fiber WAN, and

could support a point-to-multipoint base station for field

area remote radios. In this example, the Tower is being

used to provide microwave connectivity to Substation A

rather than extending fiber-optic cable across the river.

A point-to-multipoint base station at Substation A

connects to the fiber-optic network over the microwave

link for backhauling data from capacitor banks and

reclosers in the area. This topology is needed because

the devices do not have line-of-sight to each other due

to the abundance of trees in the area, thus making a

mesh network not feasible.

Leased LTE cellular service is used to communicate with

distribution switches. The area is cost-prohibitive to reach

with the network established at Substation A and B.

spectrum at 902-928 MHz, 2.4-2.5 GHz and 5.7-5.9 GHz.

Frequencies below 900 MHz can reach longer distances

and do not necessarily require line-of-sight for functional

radio path. These signals can penetrate some

obstructions, an advantage in urban and forested areas.

Lower frequencies generally offer lower channel capacity

than higher frequencies. Higher frequencies generally

offer more bandwidth and higher data rates, but require

line-of-sight and shorter paths.

When evaluating radio technology, it is important to

understand that the range, bandwidth and other

performance specifications stated by vendors are usually

based on tests conducted in a lab environment under

ideal conditions. Every environment is different;

understanding how the products will perform in the

real-world field environment is vital when planning

a network. This understanding is best obtained through

design field testing.

Leasing services from a public carrier is an option for

deploying a private wireless network. Procuring carrier

services can be accomplished fairly easily, but it is

important to understand what data security, reliability

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 NETWORKHow 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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DESIGN: BALANCING RELIABILITY, SIZE AND COSTElectric utilities are measured by metrics that include

system average interruption duration index (SAIDI),

system average interruption frequency index (SAIFI)

and customer average interruption frequency index

(CAIFI). Utilities have made large investments in energy

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

with the challenges of a changing distribution paradigm.

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BIOGRAPHIES 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

utilities includes land mobile radio design, automated

metering systems, cellular data networks and broadband

wireless networks. He also has experience in substation

design, distribution automation and energy

management systems.


FACTORS TO CONSIDERConsider 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

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