IEEE Power & Energy Magazine - March_April 2020

Volume 18 • Number 2 • March/April 2020



magazine MAIN PHOTO—©ISTOCKPHOTO.COM/RADACHYNSKYI, ©ISTOCKPHOTO.COM/AISLAN13
TOWERS—©ISTOCKPHOTO.COM/ROCCOMONTOYA
Volume 18 • Number 2 • March/April 2020
www.ieee.org/power

on the
cover

22

features 53 Transmission Technologies contents
and Implementations
22 A Digital Transformation By Renchang Dai, Guangyi Liu,
at New York Power Authority and Xing Zhang
By Bruce Fardanesh, Adam Shapiro,
Philip Saglimbene, Ricardo DaSilva, 60 A Large-Scale Testbed
George Stefopoulos, and Ahad Esmaeilian as a Virtual Power Grid
By Fangxing Li, Kevin Tomsovic,
31 The Optimization of Transmission and Hantao Cui
Lines in Brazil
By Carlos Kleber Arruda, Luís Adriano 69 Energy Storage Control Capability
M.C. Domingues, Arthur Linhares Esteves Expansion
dos Reis, Farith Mustafa Absi Salas, By Jan Alam, Patrick Balducci,
and João Clavio Salari Kevin Whitener, and Steve Cox

43 Power Transmission Technologies
and Solutions
By Bruno Meyer, Jean-Yves Astic, Pierre Meyer,
François-Xavier Sardou, Christian Poumarede,
Nicolas Couturier, Mathieu Fontaine,
Christian Lemaitre, Jean Maeght,
and Clémentine Straub

Line Maximum Power Flow (MVA)1,000 Thermal Limit on Power Flow Independent of Length columns &
800 departments

600 Power Flow Limited by
Power-Flow Electrical Effects for
Long ac Lines
Limited by
Power Flow Limit 25% of
400 Thermal Thermal Rating for 4 From the Editor 82 Book Reviews
Rating for 1,000-km Line 8 Letters to the Editor 84 Awards
12 Leader’s Corner 87 Calendar
Shorter Lines 345-kV Transmission Line 16 Guest Editorial 96 In My View
Maximum Power-Flow
200 Dependence on Length

0 96300 400 500 600 700 800 900 1,000
0 100 200 Line Length (km)

Digital Object Identifier 10.1109/MPE.2019.2959281 ieee power & energy magazine 1

march/april 2020

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IEEE POWER & ENERGY SOCIETY (PES) SFI-01681

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2 ieee power & energy magazine march/april 2020

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©ISTOCKPHOTO.COM/KOTKOAtransmission systems

advances & new technologies

TTHE FOCUS OF THE JANUARY/ ✔✔ dynamic line ratings can increase ✔✔ gases other than sulfur hexafluo-
February issue of IEEE Power & Energy transmission line thermal rat- ride can be used in substations and
Magazine was on new developments that ings, especially in overhead lines reduce greenhouse gas emissions
affect distribution systems. This issue during times of high generation
discusses transmission system technolo- by nearby wind plants ✔✔ the ability to monitor the status
gies and coincides with the IEEE Power of huge transmission networks
& Energy Society (PES) T&D Confer- ✔✔ ultrahigh voltage (±1,000 kV) and perform real-time analyses
ence and Exposition to be held 20–23 ac transmission lines and equip- can improve system security
April 2020 in Chicago, Illinois. ment can be designed to trans-
What’s new in transmission? So much port many gigawatts of power ✔✔ simulators can integrate models
has happened—it’s hard to decide where over hundreds of kilometers of many different devices into
to begin to describe the latest technologi- large-scale networks to perform
cal developments that researchers and ✔✔ condition-monitoring system ap- complex analyses
advanced application engineers have plications and analyses manage
brought us! Their work improves our maintenance and predict equip- ✔✔ modern controls for battery sys-
ability to transfer greater amounts of ment failures tems protect equipment while
power on limited rights of way through maximizing value streams for the
new construction and maximize the use ✔✔ modern protection and control various services these devices
of existing infrastructure. The digital and systems improve performance and can perform.
communications revolution provides op- maintenance practices
portunities to improve asset condition Book Review
management, system protection and con- ✔✔ research on the electromagnetic
trol, and situational awareness and analy- and thermal behaviors of con- The process of stability modeling
ses. Modern materials provide more envi- ductors expand our knowledge and analysis has changed consider-
ronmentally friendly designs and exhibit of cable design and performance ably with the widespread addition of
better performance.
march/april 2020
In This Issue

Authors representing diverse regions
comprehensively discuss the many
advances in transmission system tech-
nologies. The articles in this issue ad-
dress how

✔✔ compact line designs increase
the transfer capabilities of trans-
mission facilities, yet use con-
siderably less right of way than
traditional construction

Digital Object Identifier 10.1109/MPE.2019.2959283
Date of current version: 19 February 2020

4 ieee power & energy magazine

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apply their time and professional
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cal communities.
the increased application of flexible jor accomplishment!
Thanks
ac transmission sys- This issue Society Updates
tems, such as static var discusses A special note of appreciation to Mel
systems. Fortunately, The “Leader’s Corner” Olken, who continues to provide guid-
the revised edition of ance and tutelage, and the IEEE
column by Juan Carlos publications staff who make this pub-
lication possible. Thanks to the many
Power System Con- transmission Montero Quirós, PES contributors to this issue, especially
trol and Stability ad- system vice president for Mem- our guest editors, Sundar Venkata-
dresses these techni- technologies. bership and Image, raman, Jim Feltes, and Rafael de Sá
cal advances and other discusses many of the Ferreira, and authors. A particular
major issues. Pouyan opportunities and ben- note of appreciation to Associate
Editor John Paserba and to Robert
Pourbeik reviews this efits available to PES C. Henderson, who provides edito-
rial assistance.
book, which is suitable for graduate members worldwide and several of the
p&e
students, researchers, and practic- important new initiatives underway.

ing engineers in the power and en- PES supports all of its members and

ergy industry. provides a wide variety of benefits

but has also encouraged students,
Class of 2020 IEEE Fellows young professionals, and women to

The “Awards” column recognizes the learn and grow within our Society.

25 new IEEE Fellows who are mem- The humanitarian activities by PES

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letters to the editor share your thoughts

send comments to [email protected]

RREADERS ARE ENCOURAGED TO the whole grid architecture to address stable, reliable, and affordable future of
share their views on issues affecting the
electric power engineering profession. the symptoms. electric power systems. However, the let-
Send your letters to Michael Henderson,
editor-in-chief, at [email protected]. We have a choice: leave the current ter imputes to us several notions that we
Letters may be edited for publication.
implementation policy as is and mitigate did not, in fact, state or imply. The letter
Grid Architecture
afterward (including mod- reflects a false assump-
I found the September/October 2019
issue of IEEE Power & Energy Maga- In my opinion,ifying the grid architec- tion that we were criti-
zine (vol. 17, no. 5) to be very interesting cizing 20th-century grid
reading; it provided good back- ture with the associated
ground information and posed some
novel approaches. However, the thrust modification costs) or the energy engineering. Instead, the
of this issue seems to imply that the ex- modify the implementa- policies articles in the Septem-
isting grid architecture is the problem tion policy to take grid ber/October 2019 issue
and that the solution to our future grid
challenges is to change the existing needs into account on have done a pointed out several chal-
grid architecture to accommodate the the front end and avoid lenges that are impact-
proliferation of renewable generation
and changing customer expectations. most of the grid issues remarkable job ing requirements for grid
I do not believe that is the case. Also, at high penetration levels of stimulating operation. These require-
the articles failed to recognize that, at later. It may be prudent ments are changing, and
this time, the biggest driver to higher
renewable energy adoption is state and to require that future re- this infant our premise was that at-
federal energy policy and not necessar- newable generators be tention to operating prin-
ily economics or new markets.
designed to provide con- industry and ciples, organizational
In my opinion, the energy policies trollable capabilities sim- driving down concepts, and structure
have done a remarkable job of stimu- ilar to those of conven- is crucial to informing
lating this infant industry and driving
down renewable energy costs. However, tional generators. This renewable the decisions necessary
the anticipated grid problems are also way, we may be able to for adaptation.
created by overzealous approaches to
encouraging the adoption of renewable use renewable generators energy costs. In “Grid Architecture”
generation in California and other states. to help serve the load, [1], the author states, “New
I believe we may need to address the root
cause of the problems rather than rebuild avoid duck curve issues, developments are largely

Digital Object Identifier 10.1109/MPE.2019.2959285 and bypass the need for a separate fleet driven by evolving consumer expecta-
Date of current version: 19 February 2020
of flexible resources at very high penetra- tions, the emergence of new technolo-

tion levels. This may reduce the need to gies, and the change from central econo-

upgrade existing grid-control computer mies of scale to network economies. The

systems that are not set up to communi- latter is driven by increased penetration

cate and control large numbers of distrib- of distributed energy resources (DERs)

uted energy resources. Once these steps connected at the distribution level (‘the

have been taken, the existing grid trans- grid edge’) and by ubiquitous commu-

mission and distribution infrastructure nication connectivity. Additional drivers

may not require any major modifications. include deficiencies in resilience and in-

—Chase Sun creasing threat of cyberattack.” The letter

writer is right to point out that government

Guest Editors’ Response policy decisions give rise to new chal-

We appreciate and share our power engi- lenges and changing grid requirements,

neering colleague’s concern for the safe, as do changing economic, geographic,

8 ieee power & energy magazine march/april 2020

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climate, and technology The Design requirements power system deserves informed dis-
circumstances. The re- relationships are necessary for im- cussion by stakeholders. Grid architec-
lationships among these plementing specific ture steps back from specific designs
to provide context to review the present
sources of change are of- among these features or procedures, situation and entertain future directions
ten hard to separate. sources of whereas grid architec- for our changing world.
change are ture aims to clarify the
The articles in this context for design work —Steve Widergren and
issue were selected to by offering organizing Jeffrey D. Taft
represent challenges

that are reflected in real often hard to principles and struc- For Further Reading
discussions and trends tures that can make it
happening throughout separate.
easier to see, discuss, [1] J. D. Taft, “Grid architecture,” IEEE
the world. An objective and address systemic
Power Energy Mag., vol. 17, no. 5, pp.

of the issue was to pres- issues. Important, high- 18–28, Sept./Oct. 2019. doi: 10.1109/MPE

ent grid architecture as a discipline, impact decision making (including .2019.2921739. p&e

distinctly different from grid design. policy making) concerning a nation’s

10 ieee power & energy magazine march/april 2020

pscad.com

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leader’s corner Juan Carlos Montero Quirós

benefits of membership

how we support our members

TTHE IEEE POWER & ENERGY bers who actively participate in PES (22 April), with more than 300 co­
Society (PES) provides many oppor­ activities as well as initiatives that ordinated activities worldwide. This
tunities and benefits to its members support our remarkable achievements. anniversary commemorates our name
worldwide and continuously seeks ways Did you know that more than 40% change from the IEEE Power Engi­
to expand its support for them. PES of IEEE standards are developed by neering Society to the Power & En­
membership is truly global, with 261 PES members? ergy Society.
PES Chapters worldwide and most of
the Society’s 38,000 members residing Support for PES Students The Society also supports several
outside the United States. The growth scholarships, such as the IEEE PES
of membership in Latin America, Eu­ PES has long recognized the impor­ Scholarship Plus Initiative, IEEE PES
rope, and Asia has been very impor­ tance and value of student participa­ Erich Gunther Future Power Innovator,
tant in recent years. I am from Costa tion in its initiatives. Students not only IEEE PES G. Ray Ekenstam Memo­
Rica, Central America, and my per­ revitalize membership but also con­ rial Scholarship, and the recent IEEE
sonal and professional development tribute to and energize our activities Power & Energy Society Outstand­
have benefited greatly from my volun­ worldwide. At the end of 2019, PES ing Student Scholarship. Addition­
teerism with PES. had more than 6,000 student members, ally, students wishing to attend major
PES is the oldest and second larg­ which is one of the highest of all IEEE conferences held worldwide can re­
est of the IEEE’s 39 Societies. We are Societies. PES awards funds to student ceive support from PES, which recog­
proud of our overall numbers and the Chapters based on their local perfor­ nizes the international composition of
widespread volunteerism evident in mance. A PES Chapters Student Activ­ our membership.
our membership as well as our abil­ ities Committee also provides student
ity to attract young engineers and stu­ Chapters with resources and guidance Social Media
dents, who have revitalized our activi­ for their activities.
ties and initiatives. PES now communicates more dynami­
PES also benefits from the strength In the recent years, PES held three cally with our members using so­
of our diversity and the wide variety PES international student congress­ cial media. Social networks promote
of technical and nontechnical back­ es focused on student leaders. These Chapter activities, share information
grounds, including utilities, munici­ congresses provided opportunities for generated by technical committees,
palities, regional transmission organi­ student leaders to share their local notify the availability of high-impact
zations/independent system operators, experiences and best practices while technical reports, and recognize all of
academics, researchers, equipment learning about other cultures and es­ our volunteers. The live streaming of
manufacturers, system suppliers, gov­ tablishing bonds with leaders from international events using social media
ernment officials, regulators, test labs, other countries. This will prove valu­ enables our membership to sample var­
consultants, and many others. Our able to their careers and facilitate syn­ ious technical topics and grow profes­
strength is in attracting different audi­ ergies among regions. sionally. For example, live broadcasts
ences that share new technical ideas have been made available from con­
and best practices developed by mem­ We have already observed sever­ ferences held in Slovenia, the United
al success stories of these congress­ States, Ecuador, Bosnia and Herze­
Digital Object Identifier 10.1109/MPE.2019.2959050 es as shown by the identification of govina, and Thailand. I recommend
Date of current version: 19 February 2020 volunteers who are now integral parts following PES channels on Facebook,
of the PES organization and active­ LinkedIn, Twitter, YouTube, and IEEE
ly support global initiatives, such as Collabratec and checking for new
the 2019 IEEE PES Day celebrations

12 ieee power & energy magazine march/april 2020

••
••
••

media channels that PES will make fied by Women in Power (WiP), whose through the conferral of numerous
available soon. mission is to “foster a more diverse awards. If you know of someone who
leadership by supporting the career ad- deserves recognition for years of service
IEEE PES Young vancement, networking and education and accomplishments, visit our awards
Professionals of women in the energy industry. [The] website and submit a nomination. We are
goal is not to simply increase the num­ certain that there are many people world­
Similar to the IEEE overall, PES recog­ ber of women in the power industry but wide with major achievements better­
nizes the importance of supporting young to promote women into leadership po­ ing our world. PES has increased the
engineers in their transition from students sitions as well.” The scope of WiP goes awareness and recognition of respected
to professionals. Currently, PES has more beyond generating activities, but it also awardees, and we hope to see you at the
than 9,000 young professional members seeks to transform all levels of society awards celebrations during the PES Gen­
and volunteers who benefit from the at large. I urge all men and women PES eral Meeting.
r­esources provided to new profession­ members to join WiP.
als, which enhance their personal and IEEE PES Humanitarian
professional development and facilitate It is time to recognize the valuable Activities Committee
their integration into the professional contribution made by women in the
activities of PES. For example, PES electrical industry. Currently, roughly Because our members seek opportuni­
is one of the important sponsors of the 10% of our members are women, which ties to lead humanitarian activities all
IEEE Theodore W. Hissey Outstanding means we have an opportunity to in­ over the world, PES recently created
Young Professional Award. crease their participation in PES. the Humanitarian Activities Com­
mittee. IEEE humanitarian activities
IEEE PES Women in Power IEEE PES Awards include the IEEE Smart Village initia­
tive and IEEE MOVE (Mobile Out­
PES is also committed to equal oppor­ PES recognizes important technical, reach VEhicle), which is an emergency
tunity for men and women, as exempli­ educational, and service c­ ontributions ­relief program committed to assisting
victims of natural disasters with short-
term communications, computer, and
power solutions. The PES Humanitar­
ian Activity Committee inspires and
engages PES members to apply their
time and professional expertise and
contribute to their local communities,
especially using sustainable resources.

IEEE PES Benefits

Your membership provides access to
the latest industry developments, pro­
fessional networking opportunities,
conference discounts, and many more
benefits. One of my favorites is the PES
Resource Center, which makes available
fundamental and advanced information
at little to no cost. It is also accessible
from all over the world, and members
can receive information directly from
experts. If you have not used it, you are
missing a great source of information.

Please let me know if you have any
issue with your membership or if you
have ideas to increase PES’s benefits.
Contact me at [email protected]. As
we say in Costa Rica, pura vida! (pure
life) #MorePowerToTheFuture.

p&e

14 ieee power & energy magazine march/april 2020

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guest editorial Sundar Venkataraman, Jim Feltes, and Rafael de Sá Ferreira

transmission systems

applications of innovative technologies

TTHE FIRST TRANSMISSION LINE York Power Authority (NYPA) transmis- Arthur Linhares Esteves dos Reis,
was put into service in 1889, just a few sion system is undergoing. The authors Farith Mustafa Absi Salas, and João
years after the first gas-powered automo- discuss how NYPA is deploying inno- Clavio Salari discuss Brazil’s experience
biles were developed. While transmis- vative technologies, such as advanced with new transmission technologies in-
sion systems are a mature technology, sensors, high-speed communication cluding high-surge impedance loading
innovation has not slowed. Just as today’s systems, monitoring systems, and digital lines and dynamic line rating (DLR) de-
automobiles have little in common with control schemes, that could increase situ- vices to improve the performance of new
those first ones, except for the most basic ational awareness as well as operational and existing transmission lines. The au-
ideas of an engine and four wheels, to- effectiveness, efficiency, and the reliabil- thors present Brazil’s experience with an
day’s transmission systems employ tech- ity of assets. The authors identify five expanded bundle technology, which in-
nologies well beyond the imaginations of fundamental steps that NYPA is pursu- creases the transmission bundle size for
early electrical pioneers. ing, which any utility could also utilize to each phase with an associated boost in
Transmission systems cover vast geo- make its grid smarter. The steps are transfer capability. The DLRs represent
graphic areas and supply essential ser- another approach that has been widely
vices to power industries, raising people’s 1) deploying a robust, secure, and adopted to increase the power transfer
standard of living worldwide. The articles scalable communications network capabilities of shorter lines. The authors
in this issue of IEEE Power & Energy cite an example that combines the mod-
Magazine describe the efforts underway in 2) installing sensors and other intel- eling, analysis, and real-time monitoring
the United States, Europe, Asia, and South ligent electronic devices across the of line conductors and ambient condi-
America to improve operations and system grid to collect system and equip- tions to increase the rating of an existing
reliability, especially with the transition ment sensory data transmission line connected to a wind
from a fossil-fueled, centralized power farm. They also provide an overview of
grid to one that employs variable energy 3) enhancing grid-control devices research conducted by Brazil’s Center for
resources such as wind and solar genera- 4) using analytics, computational al- Energy Research in the electromagnetic
tion and battery energy storage systems and thermal behaviors of conductors.
(ESSs). This issue describes applications gorithms, and simulation for asset
of innovative technologies that address performance optimization The third article, by Bruno Meyer,
high levels of variable generation, over- 5) ensuring the secure deployment of Jean-Yves Astic, Pierre Meyer, François-
come the difficulties of building new lines the previous steps. Xavier Sardou, Christian Poumarede,
by maximizing the use of existing infra- The authors describe implementing Nicolas Couturier, Mathieu Fontaine,
structure, utilize sensors to improve main- innovative technologies, such as digital Christian Lemaitre, Jean Maeght, and
tenance practices, and rely on advanced substations; phasor measurement units; Clémentine Straub, discusses the latest
controls to optimize system operation. smart sensors; and the integrated smart advances in power transmission tech-
operation center, a cutting-edge com- nologies at RTE, the French transmission
In This Issue prehensive central monitoring center system operator. The article describes
that uses predictive analytics software to case studies of a dynamic line-rating ap-
The first article, by Bruce Fardanesh, forecast and prevent equipment failures plication and an interesting pilot project
Adam Shapiro, Philip Saglimbene, Ri- and significant power system compo- that integrates optical fibers with power
cardo DaSilva, George Stefopoulos, and nents outages. The authors also discuss cables to provide a real-time thermal rat-
Ahad Esmaeilian, provides a vivid pic- a simulation and testing facility that can ing of underground cables. The authors
ture of the transformation that the New accelerate the commercialization of new also discuss applying distributed flexible
equipment and technologies and also en- ac transmission devices that increase the
Digital Object Identifier 10.1109/MPE.2019.2959284 able real-time simulations of the state’s impedance of a transmission link, which
Date of current version: 19 February 2020 electrical grid.
In the second article, Carlos Kleber
Arruda, Luís Adriano M.C. Domingues,

16 ieee power & energy magazine march/april 2020

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redirects flows toward less constrained describe experiences with planning and The fifth article, by Fangxing Li , Kev-
lines, thus increasing the overall trans- operating a 1,000-kV ultrahigh-voltage in Tomsovic, and Hantao Cui, describes
mission system transfer capacity. Operat- (UHV) ac system and developing stan- a fully automated, integrated, and closed-
ed by the dispatcher in the control center, dards for line and equipment compo- loop platform with comprehensive system
commands are sent to a master controller nents. The “strong and smart grid” plan modeling as a virtual digital twin of an
with the desired level of impedance injec- shows how both UHV ac and ! 1, 000-kV actual large-scale power grid. Disparate
tion using 3G communication between UHV dc systems will serve as the back- systems can be modeled by researchers
the site and RTE’s regional control center. bone of the national grid while ensuring to analyze network performance; the ap-
reliable and stable operation. This article plications of new technologies; and the
The authors also discuss using large- describes a digital real-time simulation monitoring, modeling, control, and actua-
scale batteries that reduce the conges- system, a supercomputer with more than tion functions. The simulator achieves a
tion of lines and curtail wind gen- 24,000 CPU cores that is specialized for balance between system modeling com-
eration using various layers of control power-system parallel simulation. Mas- plexity and test fidelity for research and
mechanisms. Finally, they describe tests sive simulation cases can be parallelized testing in the following areas:
of a new fluronitrile mixture (NOVEC to conduct transient stability (TS) simu-
4710 + O2 + CO2) used in a c i r c u i t lations, electromagnetic transient (EMT) 1) the design of a decoupled soft-
breaker in a pilot substation project. In simulations, and TS–EMT hybrid simula- ware architecture to represent the
this way, they hope to reduce the use of tions. The overall simulation efficiency is large-scale power system dynam-
sulfur hexafluoride, which has been em- thousands of times faster than traditional ics and cyber control systems
ployed successfully in high-voltage sub- means. The authors also present informa-
stations for many years but is not environ- tion on an energy-management system 2) the development of a distributed
mentally friendly and listed among the six prototype, developed for installation in a messaging environment for in-
most harmful greenhouse gases. provincial control center, that is capable of tegrating interoperable software
much higher performance using a novel modules for simultaneous execu-
The next article, by Renchang Dai, database architecture along with fast par- tion and systematic testing
Guangyi Liu, and Xing Zhang, discuss- allel computational methods.
es transmission technologies and their 3) the advancement of a tool to visu-
implementation in China. The authors alize the data and interact with the
software modules in run time.

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The authors present a case study of a by lessons learned for electric utili- at a capital cost that is typically only
wide-area damping controller for damp- ties that would like to apply ESSs. The 5–10% higher than that for ACSR.
ing interarea oscillations and discuss controls coordinate the ESS operation
plans to further develop the simulator, among multiple use cases and manage The higher ratings avoid future power-
including a possible extension for future charging and discharging the ESS in a flow constraints that can otherwise
hardware-in-the-loop capabilities. manner that satisfies the requirements of occur due to the system-planning uncer-
each use case, so operational constraints tainties produced by the combination of
The final article, by Jan Alam, Pat- are not violated. increasing use of renewable generation,
rick Balducci, Kevin Whitener, and distributed generation, and open access
Steve Cox, discusses an ESS control. In his “In My View” column, Dale transmission. Examples demonstrate the
The system optimizes the physical op- A. Douglass shares the insights he advantages to using a high-temperature
eration of a 5-MW/1.25-MWh battery gained through more than 50 years of conductor. With the growing uncertainty
system to balance demands among the experience in transmission line design in generation patterns as we transition to a
battery blocks and coordinates with the and analysis. He begins with a brief lower-carbon and renewable-based power
centralized energy-management system overview of the history of line-design system, the added robustness achieved
to maximize the economic value of the optimization, the relationship of line by avoiding potential future power-flow
overall system by providing energy ar- parameters, and the amount of power constraints due to line thermal rating
bitrage, capacity, ancillary services, and that can be transmitted over a line. He could be very beneficial, especially since
system security. The authors first present then discusses conductor selection, par- it could be available for a very modest
a technical description of the ESS and ticularly comparing the capabilities of additional investment.
the use cases considered. They then pro- the widely used aluminum conductor
vide major considerations for ESS con- steel-reinforced (ACSR) to new high- We would like to extend our sincere
trol strategy development perspectives temperature conductors, i.e., aluminum appreciation to the authors and for the
and processes, including technical and conductor steel supported (ACSS). With editorial support provided by Mike Hen-
financial aspects. Actual operation re- the same conductor diameter, ACSS can derson and the IEEE Power & Energy
sults and some features of the deployed yield new lines with 50% higher thermal Magazine publications staff.
control system are presented, followed ratings and the same electrical losses,
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THE PROVEN POWER.

A Digital
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at New York
Power Authority

Digital Object Identifier 10.1109/MPE.2019.2959051 1540-7977/20©2020IEEE ©ISTOCKPHOTO.COM/AISLAN13
Date of current version: 19 February 2020
march/april 2020
22 ieee power & energy magazine

Using Innovative Technologies to
Create a More Efficient Power System

UUTILITIES TODAY ARE FACING UNPRECEDENTED levels, developing a Vision 2020 Strategic Plan for the next six
challenges due to more stringent regulations, environmen- years, and defining the optimal transformation path for adapt-
tal concerns, and a growing demand for reliable electricity. ing to this dynamic environment. In New York, these efforts
Meanwhile, according to U.S. Department of Energy’s sta- support the state’s Reforming the Energy Vision strategy for
tistics, 70% of the grid’s transmission lines and power trans- building a cleaner and more resilient and affordable energy sys-
formers are more than 25 years old. Without upgrades and tem for all New Yorkers.
enhancements, the grid will continue to age, increasing the
risk of service interruptions and limiting the integration of A vital part of this effort was the introduction of the Infra-
renewable resources. It will also be severely challenged by structure Modernization Strategic Initiative, which centers on
the intermittency of supply and the uncertainty in load. two areas: smart generation and transmission (smart G&T) and
Fortunately, many innovative and powerful new digi- asset management. Smart G&T focuses on deploying inno-
tal technologies, some of which were developed by other vative technologies, e.g., advanced sensors, high-speed com-
industries, have the potential to drastically improve the way munication systems, monitoring systems, and digital control
electric power systems are designed and operated. Driven schemes, which could increase situational awareness as well as
by these dynamics, utilities, technology vendors, and gov- the operational effectiveness, efficiency, and reliability of assets.
ernmental organizations have created a The asset management initiative seeks to develop appropriate
vision of the next “smarter” generation processes and procedures that improve the way the utility uti-
of energy delivery systems. The key driv- lizes its assets, resulting in enhanced decision making for its day-
ers of smart grid implementation include to-day operations as well as future investments. This, in turn,
the need to prepare the grid for the chal- would result in improved operational efficiencies and thus the
lenges of a changing energy transmis- creation of value for the utility and its customers. In a sense,
sion and distribution landscape, accom- the smart G&T initiative focuses more on the implementation
modating increasing levels of renewable of the foundational technical aspects, which would enable the
generation, improving system efficiency, asset management initiative to achieve its objectives.
reducing grid operation costs, boosting
reliability/resiliency, and enhancing sys- These two complementary initiatives are expected to pave
tem security. the way for increased benefits to customers by providing a
New York Power Authority (NYPA) market-leading platform for future technologies and services
is the largest state-owned utility in the by developing capabilities in the following six areas:
United States and owns and operates close
to 6,000 MW of generation, mostly hydro- ✔ increased reliability and resiliency
electric, and 1,400 circuit miles (roughly • advanced transmission monitoring, control, and pro-
2,300 km) of bulk power transmission tection systems that decrease the likelihood of cas-
from 765 to 115 kV throughout New York cading failures and wide-area blackouts
State, as displayed in Figure 1. NYPA • robust security measures that reduce the likelihood
began a series of strategic initiatives in of catastrophic bulk system failures from human-
2014 aimed at addressing the challen- caused and natural disasters.
ges that electric utilities face at multiple
✔ enhanced situational awareness
• advanced analytical tools used for converting data
from grid sensors into insight, leading to wide-area
situational awareness and control capabilities

By Bruce Fardanesh, Adam Shapiro,
Philip Saglimbene, Ricardo DaSilva,
George Stefopoulos, and Ahad Esmaeilian

march/april 2020 ieee power & energy magazine 23

• improved operator effectiveness and enhanced sys- • advanced system protection to manage intermittency
tem protection and restoration. and bidirectional power flow

✔✔ optimized transmission assets • an advanced energy management system that inte-
• ensured flexibility and efficiency by optimizing the grates distributed generation with central resources.
utilization of transmission assets
• reduced congestion and bottlenecks, which lessen the NYPA’s digital transformation revolves around the im­­
costs of operation- and maintenance-related tasks plementation of projects that support five fundamental
• reduced risk due to old equipment or necessary down- steps. These steps are typically common across many smart
time, which increases system efficiency. grid deployments:

✔✔ optimized generation assets ✔✔ deploying a dedicated utility-owned and controlled
• automatic controls and predictive maintenance cycles on high-speed communications platform
existing generation facilities to maximize performance.
✔✔ installing sensors and other intelligent electronic de-
✔✔ the integration of bulk renewables vices (IEDs) across the grid, which are used for col-
• the development of bulk renewables that meet envi- lecting system and equipment sensory data
ronmental policy requirements by using intelligent
monitoring, climate microforecasting, protection ✔✔ rolling out enhanced grid control devices
and control technologies, storage technologies, and ✔✔ effectively using analytics, computational algorithms,
advanced information and operational technologies
integrated with the underlying assets. and simulations for asset performance optimization
✔✔ ensuring secure deployment of all the aforementioned
✔✔ the integration of distributed generation
• the ability to manage distributed generation and stor- components.
age to help balance the intermittency of renewable NYPA is planning to deploy a variety of technical solu-
resources and provide grid support tions that will create a range of benefits for both the company
and New York State at large by following these five steps. To
prioritize the most beneficial, cost-worthy elements of smart
grid technologies and to ensure that the investments made

St. Lawrence-FDR Plattsburgh
Project
16 Generating Facilities
Massena
One Energy Control Center
Hundreds of Miles of Watertown
Power Lines That Deliver Energy

Niagara Project Rochester Jarvis Plant

Buffalo Syracuse Clark Vischer Ferry Crescent
Energy Plant Plant
Center
Albany

Blenheim-Gilboa

Project

Binghamton Ashokan

Project

NYPA Locations White Plains Riverhead
NYPA Power Lines

Major Cities

Small Clean Power Plants Flynn Plant
(City of New York: Six; Zeltmann Project
Suffolk County: One)

City of New York

figure 1. NYPA’s generation and transmission assets within New York State. (Source: NYPA; used with permission.)

24 ieee power & energy magazine march/april 2020

will be prudent, the necessary capability areas were first rec-
ognized and the technical solutions under those areas were
then identified. This approach allows for the development of
the most appropriate business, organizational, or technical
response to the changing utility industry landscape. The fol-
lowing sections of this article provide additional details of
these projects.

Communications Backbone figure 2. An aerial installation of optical ground wire.
(Source: NYPA; used with permission.)
The Communications Backbone project aims to deploy a
robust, secure, and scalable communications network con- operational and business data communication needs. The
trolled by the utility (as opposed to third-party providers) fiber portion consists of a hybrid solution using utility-owned
and will achieve the following objectives: optical ground wire, which is being deployed along major
transmission corridors (see Figure 2) as well as leased exist-
✔✔ replace the legacy point-to-point circuits ing unutilized fiber from other providers, typically referred to
✔✔ accommodate the data flows resulting from the in- as dark fiber. This leased dark fiber portion is fully dedicated
to the utility’s use, thus providing all of the functional advan-
creasing number of intelligent electronic devices de- tages of an owned solution while minimizing deployment
ployed through the smart G&T initiative costs and optimizing investments. The microwave portion
✔✔ enable the advanced capabilities of the Integrated of the network is being constructed as a diverse backup sys-
Smart Operating Center (iSOC), a separate project to tem or a primary system at locations with lower bandwidth
be described in more detail later in this article. requirements or where existing dark fiber is not available
The existing legacy communications technologies offered and new fiber deployment is not economically feasible. This
by third-party service providers are becoming obsolete and would be the case in regions where NYPA operates genera-
phased out by the carriers. The support and maintenance of tion assets but does not own transmission infrastructure. The
such legacy service offerings (e.g., telephone lines and 56k newly constructed microwave system will be integrated with
circuits) are becoming more challenging and costlier, thereby the existing microwave infrastructure, which, in turn, is also
forcing users to replace such technologies. Migrating to a being upgraded to meet the desired performance characteris-
new communications backbone is projected to be the most tics. Table 1 lists some details of the Communications Back-
cost-effective solution in the long run. bone project implementation.
The project also enables the following applications:
✔✔ phasor measurement unit (PMU)-based wide-area mon- Continuous Protection
itoring, protection, and control applications System Monitoring
✔✔ more advanced protective relaying schemes, such as
differential line protection using a direct fiber con- Continuous protection system monitoring (CPSM) is an unin-
nection or double-ended traveling wave protection and terrupted ac current and voltage monitoring system of digital
fault location relays that complies with North American Electric Reli-
✔✔ the large-scale deployment of field sensors such as dis- ability Corporation (NERC) PRC-005-2 Protection System
solved gas monitoring systems, temperature sensors, Maintenance requirements. The current and voltage signals
humidity sensors, weather stations, infrared (IR) cam- measured by microprocessor-based protection relays will be
eras/sensors, condition monitoring systems, generator continuously monitored and verified by comparison to an
partial discharge (PD) monitors, vibration monitoring
systems, and alarm monitoring systems
✔✔ real-time video surveillance used for physical security
or other monitoring applications
✔✔ real-time drone footage transmission.
Given outlined requirements, a combined fiber and micro-
wave backbone network is being deployed to accommodate

table 1. NYPA’s Communications Backbone project implementation details.

Optical Ground Wire (OPGW) Dark Fiber Lease Microwave

• 100-Gb/s bandwidth • 1,610+ km of leased dark fiber • 300-Mb/s bandwidth
• 1,080+ km of utility-owned OPGW • Currently 40% complete • 400+ km of microwave coverage
• C onstruction scheduled for completion • 28 microwave towers
installation; 48-strand fiber • 65 microwave dishes
• C urrently 11% complete; construction in 2020

scheduled for completion in 2021

march/april 2020 ieee power & energy magazine 25

independent source, making it possible to alarm for unac- log secondary circuits between the instrument transformers
ceptable errors or failures. The benefit of installing CPSM and protective relays. IEC 61850, Standard for Communica-
functionality at NYPA stations relates to reducing asset tion Networks and Systems in Substations, is the framework
operation and maintenance costs. The continuous automated around which a digital substation is built. By connecting
monitoring of protection systems will both reduce the fre- the various pieces of field equipment, e.g., circuit breakers,
quency of unnecessary time-based maintenance and associ- protective relays, current transformers (CTs), and potential
ated labor and travel costs as well as result in efficiency gains transformers (PTs) using optical fiber cables, the substation
during maintenance by providing real-time, standardized, layout becomes simpler, several safety issues are mitigated,
and reliable guidance and evaluation for maintenance activi- and, the implementation becomes more cost-effective in the
ties, which are typically labor- and time-intensive tasks. As case of a new substation construction.
a result, this helps to reduce the risk of major failures while
increasing overall reliability in a consistent manner across The IEC 61850 optical network operates using the Ethernet
existing protection systems. protocol. Within this framework, traditional status and com-
mand signals are transmitted using a generic object-oriented
The continuous automated monitoring of protection sys- substation event (GOOSE). GOOSE is a specific formatting
tems will also alert substation operators of real-time gradual of data that enables protection status signals to be transmitted
degradation in the performance of the protective relaying within 4 ms. This is essential to ensure the reliable and timely
system. This capability, when coupled with the state-of-the- operation of interconnected IEDs.
art asset health monitoring and diagnostics center, could help
mitigate the risk of prolonging fault conditions that cause Figure 3(a) and (b) shows the dual-redundant station and
major failures, e.g., transformer bushing failures, and thus process bus in a digital substation, which provides greater
reduce any costs associated with repair and replacement. reliability for critical substations as compared to a single
process bus. The station and process bus systems are imple-
Digital Substation mented using external Ethernet switches, connected together
in a ring configuration. The station bus allows for signals to
As a major step toward enhancing its digital capabilities, be exchanged between the bay-level IEDs and station con-
NYPA has initiated several digital substation implementa- trol, while the process bus allows communication between
tions using projects of various scales and scopes. The digital the bay-level IEDs and field devices, transducers, and other
substation concept involves digitizing a portion of the sub- equipment. Merging units (MUs) are used to collect sig-
station secondary system by eliminating the majority of ana- nals from various pieces of field equipment, including

HMI/Concentrator 1 HMI/Concentrator 2

MMS-Only Communication
(SCADA Commands,

Monitoring, and Event Retrieval)

GOOSE MMS MMS GOOSE GOOSE-Only Network MMS MMS GOOSE
All Relay–Relay Communication

GOOSE

Relay 1 Relay n Relay 1 Relay n

SV/GOOSE SV Network SV/GOOSE SV/GOOSE
MU (Optional GOOSE Trips/Status MU MU
SV/GOOSE Sent to MU and Breaker
MU Input/Output)

figure 3. A dual redundant station and process bus architecture. HMI: human–machine interface; MMS: manufacturing
message specification; SCADA: supervisory control and data acquisition; SV: sampled value; MU: merging unit. (Source:
NYPA; used with permission.)

26 ieee power & energy magazine march/april 2020

CTs and PTs. These signals are then digitized and trans- Conventional techniques of operating and monitoring the
mitted via the process bus to other devices as sampled val- bulk grid have limited capabilities for real-time problem detec-
ues (SVs). The merging unit is the interface between the tion and failure prevention. This means that there would not
traditional analog signals and the digital protective relays be enough time to react to fast-evolving events that threaten
and other IEDs. As opposed to the publisher/subscriber the stability of the system. As a result, the bulk power grid
methodology used by the GOOSE and SV protocols, the operates under conservative assumptions that do not allow for
manufacturing message specification (MMS) protocol is operating the system based on its real-time dynamic limits,
based on a client/server mechanism and typically used for resulting in congestion and inefficient asset utilization. This
higher-level, one-to-one information exchanges, such as becomes increasingly relevant and important as intermittent
those between a substation and a supervisory control and resources are integrated into the grid, thus reducing the con-
data acquisition system. trollability and predictability of available generation. Also, as
more advanced and complex control schemes are embedded
There are currently three ongoing projects that look to into the grid (e.g., power electronic-based interconnections),
incorporate digital substation architectures into existing faster transient phenomena are expected to have a more pro-
transmission substations. The first implementation is the found effect on grid operations.
switchyard automated monitoring and controls system being
installed at the 115-kV switchyard of the Robert Moses Saint In a future hierarchically centralized and coordinated
Lawrence Power Project, one of NYPA’s major hydroelectric grid operation and control scenario, one can envision that
plants. The project involves the implementation of a GOOSE sufficient, synchronized, low-latency, and trustable (cyber-
process bus and GOOSE messaging between relays as well secure) data (including breaker status or network topology
as MMS stations, while maintaining traditional hardwired data) with adequate sampling rates will be widely available
connections between the relay building and the switchyard at the operations/control center and the state estimator (the
CTs and PTs. A second project, which has already been backbone of all energy management system applications)
commissioned and is operational, involves fiber-optic CT will run with a superior performance in the subsecond even-
installations and the implementation of an SV network at cycles timeframe, providing full knowledge of the system
the Fraser Annex substation, located in central New York. state. This full-state knowledge enables very fast con-
The substation houses a series capacitor bank operating on tingency ranking and security analysis and control action
a 345-kV transmission corridor. Finally, work is currently determination, providing timely advice to the system opera-
being done on a more comprehensive IEC 61850 project as tor under both normal and emergency conditions. In the long
part of a major upgrade of a 115-kV substation in northern run, as confidence is built, some of these control actions
New York. The project includes optical CT and PT instal- may be performed automatically via direct feedback from
lations for line protection relaying, the installation of field the operations/control center. For additional grid flexibility,
merging units, and the implementation of SV and GOOSE ultimately, such closed-loop automated capabilities will be
schemes in both process and station bus arrangements. indispensable for operating power systems more reliably,
safely, and efficiently, especially in dealing with fast power
The digital substation offers the following advantages over a system phenomena and zero- or low-inertia, inverter-based
conventional arrangement: generation resources.

✔✔ easier and simpler installation (much less wiring) The phasor data captured during grid disturbances will
✔✔ interoperability between devices made by different also be used to perform system model validation for NERC
regulatory compliance. Per NERC compliance requirements,
manufacturers generator owners must periodically validate the dynamic
✔✔ improved reliability models of large generating units. This can be performed via
✔✔ improved measurement accuracy and recording of offline tests or by utilizing captured PMU data during sys-
tem disturbances. Offline, manual validation is costly, more
information tedious to perform, and requires units to be taken out of ser-
✔✔ improved commissioning and operations vice, whereas automatic validation using PMU data will be
✔✔ easy incorporation of modern electronic CT and more efficient and cost-effective.

PT sensors. Fleet-Wide Deployment
of Smart Sensors
Wide-Area Deployment of PMUs
As a major part of its digitization initiative, NYPA is cur-
Initiated in 2016, the purpose of this project was to install rently deploying additional sensors to collect data from
new PMUs that extend the system observability of the power plant equipment, substation apparatus, and transmis-
e­ xisting PMU network and also replace several vintage sion lines to enhance efficiency and extend the life of those
devices installed in the early 1990s. These PMUs provide assets by continuously assessing their performance and
valuable phasor data, which support the enhanced real-time condition status. A full suite of sensors is being installed on
monitoring and operation of the grid and, when combined
with other analysis and control tools, help increase power
flows over existing interfaces, alleviate congestion, and
improve grid reliability.

march/april 2020 ieee power & energy magazine 27

equipment, e.g., turbines, generators, transformers, reactors, galloping detection systems have been installed at the com-
circuit breakers, battery banks, underground/underwater pany’s assets fleet wide. By networking these sensors to the
cables, and overhead transmission lines, as depicted in Fig- iSOC, it is expected that more than 130,000 data points will
ure 4. Sensors, e.g., dissolved gas analyzers, temperature, be transmitted to this new monitoring and diagnostic hub.
pressure, and vibration monitors, PD and acoustic sensing, The iSOC currently collects more than 45,000 data points
IR cameras, dynamic line rating equipment, and icing and spanning the New York State grid and feeds the data into

More Than 900 Sensors Across Major Assets

Generators and Turbines Cable and Overhead Lines
Partial Discharge Dynamic/Forecasted Rating
Vibration Air Gap Tilt and Vibration Detection
Rotor Flux Icing and Galloping Detection
Pressure and Temperature Cable Leak Detection
Precatalyst Emission Cable Fault Detection
Total Sensors: 140 Total Sensors: 50

Transformers Circuit Breakers Battery Banks
Dissolved Gas Analysis SF6 Pressure Density Specific Gravity
Winding Temperature Contact Wear/Timing Electrolyte Level and Temperature
Bushing Monitor Motor Runtime Ground Fault
Partial Discharge Coil Continuity Intercell and Total Resistance
Thermal Camera Cabinet Temperature Current and Voltage
Total Sensors: 443 Total Sensors: 248 Total Sensors: 79

figure 4. The sensor types and total number of major assets. SF6: sulfur hexafluoride. (Source: NYPA; used with permission.)

28 ieee power & energy magazine march/april 2020

state-of-the-art analytics engines. In the center, analysts
and engineers look at the near-real-time performance of the
various monitored pieces of equipment and compare it to
their predicted performance, spotting potential issues often
well before conventional scheduled preventive mainte-
nance would detect them. The data shows up on an impres-
sive 81-ft-long LED display screen, enabling iSOC staff to
visualize various data from different sources concurrently
and more effectively analyze and extract information from
such data.

iSOC figure 5. The iSOC at NYPA’s offices in White Plains, New
York. (Source: NYPA; used with permission.)
The iSOC, located at NYPA’s offices in White Plains, New
York, is a cutting-edge comprehensive central monitoring avoidance and performance improvement is a fundamental
center, as shown in Figure 5. The center, which opened in driver of the benefits NYPA intends to achieve through its
December 2017, uses predictive analytics software to fore- broader strategic plan.
cast and prevent equipment failures and significant outages
at power plants, substations, and transmission lines, provid- A combination of predictive analytics tools using phys-
ing the technological ability to predict and remedy with a ics-based and machine-learning algorithms enables iSOC
higher level of efficiency. This enables effective scheduling analysts and engineers to notice trends in how a piece of
of repairs, lowers maintenance expenses, and reduces oper- equipment is operating. The desired outcome of processed
ating risks, thus helping the utility to keep costs down, trans- data aims to reveal valuable insights into any incipient prob-
lating to savings for its customers. lems and gauge the life expectancy of equipment based on
historical and current operating patterns, which might differ
One of the fundamental goals of the asset management from manufacturer specifications.
initiative is to harness improved decision-making capabilities
by aggregating various sensory data streams to monitor, diag- Predictive analytics also offers an opportunity for more
nose, and inform asset repair or replace decisions. Achieving sophisticated outage scheduling processes. For instance, if
this goal and realizing the associated benefits are reliant upon the data indicate normal performance, the manufacturer’s
a robust integrated data analytics platform and decision sup- calendar-based replacement or maintenance schedule could
port tools. Creating a strong data foundation that allows for be reduced. Conversely, if the data indicate an issue with the
data analysis, visualization, association, and sharing across health of an asset, then maintenance should occur before the
the organization requires a combination of data cleanup next scheduled service. In extreme circumstances, the equip-
efforts and the deployment of modern analytical and visual- ment can be shut down immediately to avoid a catastrophic
ization tools. The iSOC provides enterprise-wide technology failure that could result in loss of service for longer periods.
and service management capabilities across the company’s
operational groups and plays a critical role in identifying, The iSOC may initially receive hundreds of advisories
managing, coordinating security incidents and events on com- per day on potential service issues. With the trending data,
mon devices, infrastructure, networks, and applications where analysts and engineers can determine what caused an alarm,
one or more operational groups have an interest. what it means, and how it should be addressed. Most alarms
may be inconsequential, but two or three instances may be
A key feature of the iSOC, compared to more traditional focused on for further detailed examination. This supervised
utility monitoring and diagnostic centers, is its additional learning and tuning process would gradually reduce the
multifunctional, multidiscipline capabilities, which include number of false positive alarms as more data are collected
the monitoring and management of communication networks over time.
and IT infrastructure as well as physical and cybersecurity.
Such functionality variety is crucial for supporting the cen- Advanced Grid Innovation
ter’s role as an integrated operations center. These diverse Lab for Energy
capabilities and functionalities hosted within the iSOC make
it the central nervous system of the smart grid, constantly In pursuit of its digitization goals and to support the R&D
monitoring sensors, devices, and communication paths to effort required to face the challenges of digitization, NYPA
alert and suggest corrective actions to an operator when has launched the Advanced Grid Innovation Lab for energy
faults or other problems occur. This increased awareness (AGILe). Established in 2017 as a collaborative i­nitiative
helps to streamline operational performance, reduce annual led by NYPA and supported by additional stakeholders,
and unexpected operating costs, increase general asset per- AGILe is a power systems laboratory that includes simula-
formance and reliability across the fleet, and mitigate the tion and testing facilities. The lab provides electric utilities,
impact of catastrophic events. This kind of cost reduction/ governments, universities, high-tech businesses, and others

march/april 2020 ieee power & energy magazine 29

technology vendors, and research organizations together
to work on common challenges and opportunities that can
improve the performance, security, and efficiency of the
electricity grid.

figure 6. AGILe, the power systems laboratory located at Summary
NYPA’s offices. (Source: NYPA; used with permission.)
Like other utilities, NYPA has embarked on a digital jour-
from around the world with a wide range of R&D tools. The ney in technical areas of grid monitoring/operations/con-
research work performed in the lab can help strengthen infra- trol as well as business enterprise to take advantage of the
structure, fast track the commercialization of new technolo- efficiencies from the effective use of information and data.
gies, and expand renewable energy integration. The work per- Although this is a bold endeavor for a conservative indus-
formed at AGILe will accelerate improvements to New York’s try in terms of adopting new technologies, the benefits are
energy infrastructure and lead to a more reliable and efficient starting to be realized through asset health and longevity
electric grid. enhancements, operation and maintenance and capital sav-
ings, and enhanced tools and methodologies for grid opera-
The specific general research areas at AGILe include tion and control. This journey is envisioned to ultimately
advanced transmission applications, cybersecurity, substation result in a safer, more reliable, more secure, and more effi-
automation, sensors, and power electronics controllers. cient power system.
AGILe is located at the White Plains offices, as shown in Fig-
ure 6, and comprises a digital real-time grid simulation lab, For Further Reading
which will enable real-time simulations of New York State’s
electrical grid. It is initially targeting transmission- and dis- “Infographic: Understanding the grid,” U.S. Department of
tribution-level research focusing on power system wide-area Energy, Washington, D.C., Nov. 17, 2014. [Online]. Available:
monitoring and control, synchrophasor applications, renew- https://www.energy.gov/articles/infographic-understanding
able energy integration, and substation automation and con- -grid
trol. AGILe has the potential to provide grid benefits, e.g.,
accelerating and streamlining the deployment of new equip- B. Fardanesh, “Future trends in power system control,”
ment and technologies, analyzing peak demand stress, incor- IEEE Comput. Appl. Power, vol. 15, no. 3, pp. 24–31, 2002.
porating intermittent resources, and improving reliability and doi: 10.1109/MCAP.2002.1018819.
bulk system control.
S. Ghiocel et al., “Phasor-measurement-based state es-
The lab will help deliver the following capabilities timation for synchrophasor data quality improvement and
and outcomes: power transfer interface monitoring,” IEEE Trans. Power
Syst., vol. 29, no. 2, pp. 881–888, 2013. doi: 10.1109/TPWRS
✔✔ advanced modeling of power grid components .2013.2284098.
✔✔ real-time simulations of New York State’s electri-
B. Fardanesh, “Direct non-iterative power system state
cal system solution and estimation,” in Proc. IEEE Power and Energy
✔✔ hardware-/software-in-the-loop equipment testing Society General Meeting, San Diego, CA, July 2012, pp. 1–6.
✔✔ the emulation and performance characterization of doi: 10.1109/PESGM.2012.6345757.

power grid data communication schemes “Smarter energy infrastructure: The critical role and
✔✔ automated controls that improve network resiliency, value of electric transmission,” Edison Electric Institute,
Washington, D.C., Mar. 2019. [Online]. Available: https://
security, safety, and efficiency www.eei.org
✔✔ the integration of large-scale renewable energy re-
Biographies
sources as well as distributed energy resources
✔✔ a high level of situational awareness that enables opti- Bruce Fardanesh is with the New York Power Authority,
White Plains.
mal grid operation under various conditions.
It is envisioned that AGILe will create a collaborative re­­ Adam Shapiro is with the New York Power Authority,
search environment that brings utilities, academic institutions, White Plains.

Philip Saglimbene is with the New York Power Author-
ity, White Plains.

Ricardo DaSilva is with the New York Power Authority,
White Plains.

George Stefopoulos is with the New York Power Authority,
White Plains, New York.

Ahad Esmaeilian is with Avangrid, Orange, Connecticut.

p&e

30 ieee power & energy magazine march/april 2020

The Optimization
of Transmission
Lines in Brazil

Proven
Experience
and Recent
Developments
in Research
and
Development

IIN THE LAST TWO DECADES, ©ISTOCKPHOTO.COM/GUSTAVO_ASCIUTTI
the Brazilian power sector has under-
gone a major transformation, insti- projects, which have resulted from continued research that
tuting more thorough processes for Centro de Pesquisas de Energia Elétrica (CEPEL) has been
the licensing and construction of conducting for decades on the measurement, monitoring, and
new transmission lines, stricter stan- uprating of transmission lines.
dards for electromagnetic (EM) fields in the vicinity of these
lines, and harsher regulatory penalties for unscheduled power
outages. This article describes concepts that are being applied
in Brazil in the design and construction of new transmission
By Carlos Kleber Arruda, Luís Adriano
M.C. Domingues, Arthur Linhares Esteves dos Reis,

Farith Mustafa Absi Salas, and João Clavio Salari

Digital Object Identifier 10.1109/MPE.2019.2959052
Date of current version: 19 February 2020

march/april 2020 1540-7977/20©2020IEEE ieee power & energy magazine 31

In practice, an even electric field distribution is not feasible
because each subconductor would need to be equidistant
from other phases, ground, and structures.

The High Surge-Impedance conventional line designs. HSIL technology globally opti-
Loading Concept mizes all significant electrical and geometric parameters of a
transmission line, resulting in optimal choices for the diame-
The factors limiting the power-transfer capability of a trans- ter of the conductors’ cross section, phase spacing, height, and
mission line can be broadly classified into three categories: sag. HSIL design became possible with recent advances in
modeling, calculation methods, and computational resources.
✔✔ Ampacity limits refers to a maximum current estab- Such tools allow engineers to establish transmission-line con-
lished to prevent the maximum design temperature figurations optimized with respect to electrical and magnetic
from being exceeded, either for conductor damage or field distributions and, consequently, transmission capacity,
clearance violation; this limit is relevant for lines of electrical parameters, and current distribution.
short length (<100 km).
The HSIL concept represents a considerable change in
✔✔ Systemic constraints apply mainly to stability limits re- transmission-project development and operating practices,
lated to system configuration and operating point. and its adoption requires the integration of planning, design,
maintenance, and operation to obtain the most benefit. The
✔✔ Voltage drop occurs in medium and long transmission HSIL design consists of a geometric (defined by the electric
lines due to the reactive power demanded by the line requirements) and mechanical optimization. The geometric
inductive reactance. phase is defined mainly by the surface electric field distribu-
tion and the insulation coordination (distance between con-
The system constraints and voltage drop are more commonly ductors, conductors and grounded structures, and conductors
binding in systems with large renewable power sources located and ground). After a number of iterations, a final mechanical
far away from load centers. Historically, this is the case for design was obtained for test trials, as shown in Figure 1.
remotely located hydropower in Brazil; however, technologi-
cal solutions are available to deal with such limitations. For Experience shows that two main geometric factors im­­­
instance, voltage drop is usually addressed by means of series prove the SIL: compacting the phases and expanding the
compensation or flexible ac transmission system. conductors’ bundles. The concept of compact lines applies
mainly to new designs since the phases’ positions are in­­
For such long lines, there is a certain power-transfer level fluenced by the structures, whereas the expanded bundle
where reactive power generated in the line capacitance (EXB) can be utilized in all types of lines, as the phases’
equals reactive power absorbed in line inductance, such that centers of gravity are unaltered. Both approaches alter
no reactive compensation is required. This power rating is the surface electric field, which could be expressed by a
related to the line characteristic power, or surge-impedance utilization factor ku, which is the relationship between
loading (SIL). In circuit theory, when the receiving load the ­surface electric field with the theoretical maximum
matches the SIL value, a maximum power transfer is reached for each subconductor (see Figure 2). An ideal utilization
for this voltage level. In practice, other factors influence the (ku = 1) implies a linear power increase in relation to the
maximum power transfer. But for long lines, it can be stated number of subconductors. In practice, an even electric
as a proportion of its SIL. field distribution is not feasible because each subconductor
would need to be equidistant from other phases, ground,
The R&D projects described here allowed for the design and structures.
of optimized lines with very high SIL, called HSIL lines.
The additional transmitted power is due to the maximum Given an assumed horizontal phase arrangement, Fig-
utilization of the electric field around the conductors; the ure 2 summarizes the theoretical and achievable SIL as a
optimum point is close to the corona-onset threshold. function of the number of conductors per bundle. The figure,
Because the corona effect also depends on weather condi- based in a hypothetical configuration, also shows how dif-
tions, proper knowledge of the statistical distribution of tem- ferent design approaches for the bundled conductors affect
perature, air density, and humidity enables transmission-line the SIL and provides examples for bundles of four and eight
design closer to its limit, with a margin to avoid overloading subconductors per phase.
during operation under different weather conditions. The
occurrence of corona in a line is tolerated only under very- When the geometric concept is followed, the insulation coor-
high-humidity conditions or heavy rain, as an all-weather dination analysis must verify the required clearance between
corona-free line design is economically unfeasible. phases and grounded structures, along with the length of the

The HSIL concept optimizes the electric field on the sur-
face of each conductor to increase the power-transfer capabil-
ity with lower cost per megawatt delivered as compared with

32 ieee power & energy magazine march/april 2020

Initial Concept • Power

• Voltage

• Structure Type

• Hardware
Configuration

Optimized
Project

Conductor
Selection

Final Tower Initial Tower • Bundle
Geometry Geometry Optimization

• Insulation
Coordination

• Electric Losses Technical and Structural Weight
• Maximum Economic
Analysis Minimum
Temperature Conductor Height
• EM Fields and Right of Way
• Material Costs

figure 1. The workflow for the optimization of a transmission-line project.

insulator strings. The examined ku = 1 (a)
weather conditions include a group 4 (b)
of stochastic parameters that must
be considered in a statistical analy- SIL (Ground Wire) 3 (e) (c)
sis of design requirements, that is, (d)
meeting criteria for allowable 2 (c) (d)
(b) (e)
✔✔ fundamental frequency over- 5m
voltages that permit no fail- 1 (a)
ures at maximum operating
voltage and consider the ef- 0 15
fects of wind and pollution
5 10
✔✔ overvoltages due to switch- ns
ing transients from ener-
gization or reclosing that figure 2. The relation between SIL and number of subconductors, ns, for different
must meet prescribed risks design approaches. (a) A conservative design using standard hardware and evenly
of failure distributed spacing. (b) An EXB, still restricted to a regular shape. (c) A fully optimized
design with irregular bundles, resulting in a maximum SIL. (d) Another example of a
✔✔overvoltages caused by conservative design using standard hardware and evenly distributed spacing. (e) An
lightning discharges related additional EXB design, still restricted to a regular shape.
to direct or indirect strikes
(back flashover) that con-
sider a maximum number
of expected outages rela­
ted to the local lightning-
strike density.

march/april 2020 ieee power & energy magazine 33

CEPEL, together with the Brazilian utility Eletrobras and its
subsidiaries Companhia Elétrica do Rio São Francisco and
Furnas, has been developing EXB applications.

After the distances between conductors and the support lines. Additionally, combining compact line designs and the
structure are determined, a mechanical optimization is use of EXB (HSIL/EXB) may provide advantages from the
used that includes selection of towers and poles. In this system viewpoint, including
step, the support total weight is minimized, with several
loadings considered, including longitudinal, transversal, ✔✔ the reduction or avoidance of series compensation, al-
and vertical forces under nominal and contingency modes, lowing direct economic benefits, such as the absence
that is, a conductor falling. Indirectly, the foundations are of subsynchronous resonance (SSR) problems as well
also optimized. as the elimination of maintenance and replacement
costs of additional network equipment
At the beginning of compact line development, the
design focus was on the transmission of large blocks of ✔✔ an increase in voltage support due to its electrical
energy over long distances. However, in the following characteristics, reflected in the increased power-trans-
years, CEPEL, together with the Brazilian utility Eletro- fer capacity of the transmission line.
bras and its subsidiaries Companhia Elétrica do Rio São
Francisco (CHESF) and Furnas, has been developing EXB For the design of a new transmission line, the optimiza-
applications for new high-capacity transmission lines and to tion of EM parameters can achieve a better field distribu-
uprate the transmission capacity of existing transmission tion and a higher SIL, resulting in an increased transmission
capacity compared to traditional designs for the same volt-
age level. For refurbished transmission lines, HSIL tech-
nology also provides opportunities for increasing transfer
capabilities that depend on the transmission-line design.
Options may exist for rearranging conductor configurations
or adding one or more conductors per phase, which need
not necessarily be of the same type as the original conduc-
tor. The latter approach provides all of the advantages of
HSIL design by increasing transmission capacity, including
thermal limits. In addition, the adjustment of line param-
eters in the same transmission corridor can improve voltage
levels in strategic buses, eliminate economic dispatch con-
straints related to SSR, reduce voltage sags, and improve
stability performance.

figure 3. An EXB convertible line of 2 × 230 kV and Field Experience
500-kV structure. (Source: CEPEL; used with permission.)
CHESF was an early adopter of HSIL technology. The Bra-
zilian company focused on the EXB technique and adopted
it in new and uprated transmission lines, which played an
important role in meeting the utility’s needs. The first com-
mercial application of the EXB technique was employed
in the city of Fortaleza in 1995. At that time, the city was
served by three 230-kV lines from the Paulo Afonso hydro
plant, which was 660 km away. The increase in demand in
Fortaleza required a generation upgrade and a new 500-kV
line from the North region of the Brazilian grid, called the
North–Northeast (N-NE) interconnection. This planned line
would have completed a 500-kV ring to improve reliability
of the local system.

Repeated delays in the construction of the N-NE circuit,
coupled with growing demand, led to a critical situation in
Fortaleza. The problem was successfully resolved through
application of EXB, using a “convertible” technique. A

34 ieee power & energy magazine march/april 2020

For the design of a new transmission line, the optimization
of EM parameters can achieve a better field distribution and
a higher SIL, resulting in an increased transmission capacity.

230-kV double-circuit line with low series reactance was With the increased use of HSIL technology, CHESF, Ele-
installed on existing 500-kV structures. The four-subcon- trobras, and CEPEL developed metrics for assessing these
ductor bundles per phase were expanded, forming a dou- projects. Measurements of EM levels are used to calibrate
ble circuit with two subconductors per bundle (Figure 3). the models and demonstrate the efficacy of the design to the
This solution increased the power-carrying capability to general public.
Fortaleza by 25%. The efficacy of the EXB solution was
proven through the reduced need for static compensation In 2003, Furnas installed its first HSIL/EXB 500-kV line
and better current distribution in the corridor’s transmis- with four aluminum conductor steel reinforced (ACSR) rail
sion facilities. Finally, in 2000, the Presidente Dutra–For- conductors (954 kcmil) per phase between the Cachoeira
taleza line, 740 km long, was converted to 500 kV by using Paulista and Adrianópolis substation; it is 350 km long and
EXB (Figure 4). uses a series of structures called cat face towers. This alter-
native increased the standard SIL from 900 to 1,200 MW by
Today, several companies in Brazil employ EXB designs, employing a very light and flexible self-supporting structure
proving their acceptance. For instance, the 500-kV line Bar- compared with other structural patterns of the same capacity.
reiras II–Rio das Éguas–Luziânia, with an EXB utilizing six
subconductors, was commissioned by Consórcio Paranaíba in In 2009, Furnas installed a 500-kV pilot line with a com-
2018. Future applications of this technology looks promising. pact configuration, fully optimized with six ACSR rail con-
ductors in a cross-rope tower. The asymmetric arrangement

(a) (b)

figure 4. A 500-kV EXB HSIL line in northeastern Brazil. (a) and (b) Different angles from the same line. (Source: CHESF;
used with permission.)

march/april 2020 ieee power & energy magazine 35

figure 5. The test setup of the Furnas 500-kV compact line at Seropedica, Rio de Janeiro, using a cross-rope tower.
(Source: CEPEL/Furnas; used with permission.)

figure 6. A UHV dc mockup at the UHV laboratory. (Source: CEPEL; used with permission.) march/april 2020
36 ieee power & energy magazine

also featured midspan bundle expansions: near the tower,
the bundles are smaller, with a special spacer used to enlarge
the bundle size midspan. This gives an “average bundle”
performance without enlarging the structures. Figure 5 shows
the test setup for this line.

The development of new geometries cannot be limited to
a theoretical model. Following the R&D cycle, laboratory
tests are conducted using tower mockups and normalized
voltage sources under controlled conditions. Since its con-
ception, CEPEL has provided a full range of laboratories.
The newest addition of an ultrahigh voltage (UHV) labora-
tory (Figure 6) can perform tests up to 1,100 kV ac and
800 kV for dc lines.

Dynamic Line-Rating Techniques (a)

The HSIL concept is well suited for application in the case (b)
of long lines. Shorter lines will have power transfer limited figure 7. Examples of the sensors used for real-time moni-
by the conductors’ thermal rating, which demands a differ- toring (a) before installation and (b) on the line. (Source:
ent approach. CEPEL/CHESF; used with permission.)

Increased transmission capacity can generally be achieved important connection lines to these generation plants were
using dynamic line-rating (DLR) techniques, which is now being delayed, while, at the same time, more wind plants
a mature technology that uses current/temperature sensors were being installed. This posed two important problems.
(Figure 7) and real-time monitoring to establish the true First, without new transmission lines, the potential output
transmission-line limit. However, this solution should be of power produced by the wind farms would be wasted at
used with caution because of of differences along the line in a time when hydraulic generation was constrained due to
atmospheric conditions, span lengths, and vegetation growth, reduced reservoir levels and low inflows. Second, the con-
all of which have a direct influence on conductor tempera- tracts ensured that generators would be paid as soon as the
ture, which can vary widely along the line. A transmission generation equipment was available, even if the transmis-
line may be limited by a single critical span or by a few spans sion grid could not accommodate their production.
that require the adoption of special measures.
In the case presented here, a wind farm was installed
Since conductor temperature may affect line integrity on the coast near Natal, and the scheduled transmission
and also, more importantly, endanger safety due to potential
fires, DLR uprating must be used very carefully. Transmis-
sion-line static line ratings are normally established with
conservative assumptions due to these safety considerations.
Cases in which less conservative assumptions are used can
result in DLRs being lower than the static ratings some of
the time.

There are some special conditions under which the appli-
cation of DLR is both safe and efficient. A real-life example
is presented in which the combined application of model-
ing tools and real-time monitoring allowed for an increased
transmission-line capacity in the connection of wind-power
generation plants to Brazil’s national grid.

A huge potential for wind-power generation was identified
in the Northeast region of Brazil, and several wind plants are
being developed in the region. Expanding the transmission
system to collect this energy production and connect it to the
national network has been a challenge. Transmission lines
of 69, 138, 230, and 500 kV are being designed and built to
allow for proper flow of the energy generated in these wind
farms to load centers.

Due to problems associated with the legal schedules for
environmental licensing and acquisition of land-use rights,
including indemnities, the construction and operation of

march/april 2020 ieee power & energy magazine 37

variable thermal ratings allowed

Generation ETD NTT Load Center increases of up to 50% in wind ge­­
Collector neration capacity and virtually elimi-

Overloaded National nated the restriction of the power
Postponed Network generated by the wind farms con-
nected to this line.

The maximum power genera-

tion in these wind power plants

always occurs with higher winds

(between 8 and 12 m/s) at the height

level of the wind turbines. Because

figure 8. A schematic diagram of 230-kV wind-plant feeders to the Estremoz II of the favorable profile of terrain
(ETD) and Natal III (NTT) substations. along the line route, it is expected
that the wind speeds reaching the

line conductors will be consider­

reinforcement was delayed for 18 months, leaving the old ably higher than the conservative design criteria of 1 m/s.

transmission lines as the only option for connecting the gen- Thus, the current capacity in the line is likely higher than the

eration plant to the main transmission system for a consid- values considered in the worst-case criteria and would not

erable period. Transmission-system studies and load-flow violate the maximum permissible temperature of the conduc-

analyses showed that a 16-km-long, 230-kV line was a bot- tor and minimum safety distance to ground of this design.

tleneck between large collector substations and the national For example, for a 3-m/s wind speed, the line can transmit

network. A short-term increase of this line capacity was 738 MVA, 47% higher than the original static line-rating cri-

strongly desired. teria, without violating safety clearance and design tempera-

The postponement of the transmission reinforcement via ture requirements.

a second circuit of the 230-kV Extremoz II–Natal III and the This hypothesis had to be corroborated by field measure-

imminent increase of wind generation injected into Extremoz ments and correlations between the different variables of inter-

could overload the first circuit; this could be relieved only est. Real-time measurements of current and temperature of the

by significantly restricting generation, as shown in Figure 8. conductors were performed. Consideration of a higher wind

The line’s thermal static rating was 502 MVA for a twin velocity with the other meteorological variables (solar radiation,

bundle with two all aluminum alloy conductor Flint ambient temperature) unchanged was used to determine a DLR.

740-kcmil conductors. This constant rating was calculated The time plots of Figure 9 indicate a correlation between

using an assumed wind speed of 1 m/s perpendicular to the line. two monitored variables: conductor current (Ipd) and tempera-

By allowing the line’s thermal rating to vary with wind ture for the duration of a day. Under these conditions, the real-

speed, it was shown that the line rating was correlated with time monitoring reveals a possible latent increase in capacity

the wind-turbine generation level. As a result, the use of corresponding to the 15 °C difference between the tempera-

ture predicted by the standard rating methodology (Testim) and

the measured temperature (Tpd), which could be explored to

increase power transfer.

450 45 The analysis of these initial monitoring data led to the
40 consideration of allowing line transfers up to 680 MVA,
400 equivalent to 1,706 A/phase or 853 A for each conductor
350 35 in the bundle under high wind generation conditions, while

I (A)
t (°C)
300 30 maintaining a safe, conservative approach. This increased
250 25 value was designated as conditional capacity and rep-

200 20 resented a 35% uprate relative to the nominal capacity of

150 15 631 A per subconductor in the bundle, calculated with the

100 10 original design criteria and used for long-term applications
0 2 4 6 8 10 12 14 16 18 20 22 (steady-state operation of the network).
(Hour)
As an evaluation of this initial effort, between December

Ipd (A) Tpd (°C) Testimated (°C) 2014 and mid-January 2015, line current values exceeded

the original nominal rating for 13 days. During this period,

figure 9. The current and temperature daily profile: blue since the wind speeds were favorable, the conductor tem-
indicates the current, red represents the measured conduc- peratures under higher currents did not reach the design tem-
tor temperature, and orange shows the estimated conduc- perature of 61 °C, defined for calculations of allowable sags

tor temperature according to the design methodology. and safe distances during the monitoring period.

38 ieee power & energy magazine march/april 2020

The maximum registered overload during an outage of The analysis of the data obtained in the monitoring pro-

another line in the region was 1,700 A/phase (+34.5% over cess points to some important characteristics of the physical

the nominal rating), very close to the allowed conditional phenomena that deserve attention, since they involve safety

capacity of 1,706 A/phase. The measured temperature of considerations. The general assumption that high-generation

conductors was approximately 50 °C, due to the extra cool- periods are necessarily associated with high wind velocities

ing with wind speeds higher than the 1-m/s criterion. This must be properly verified in practice. Only this will ensure

extra transmission capacity has allowed more than 2,200 MWh that the conductor cooling will be sufficient, leading to

of renewable energy to be supplied to the system that other- higher line capacity in general.

wise would be wasted. However, the dynamics of the process have important excep-

Based on the good initial results of these efforts, additional tions. The most important of these is when a rapid increase in

equipment was installed. An instrument for current and tem- wind speed at the generation plant, typically the arrival of a

perature real-time monitoring and two weather stations were headwind, causes rapid growth of the generated power at the

brought into operation, thus making it possible to obtain infor- wind farm. This increases the current in the line almost instan-

mation from two locations close to the line terminals. The new taneously, while the wind will arrive over the length of the line

acquired data allowed for more accurate and reliable informa- in time gaps up to 20–30 min. In this interval, the heating of

tion and analysis. The data confirmed that the weather condi- the conductors can be considerable and undesired.

tions were similar along the entire line length and also included The inverse situation, where the wind suddenly drops

the actual temperature of the conductors. Also, it was clear that down, will keep the current up for some time, due to turbine

when the current increased due to higher wind generation, the inertia, and the conductors will generate considerable internal

wind at the conductor’s height also increased to some extent. heating while rapidly losing some of their cooling capacity.

Thus, the cooling of conductors was better, and the conductor However, this type of event will have a much shorter duration,

temperatures did not increase as much as predicted using the on the order of a few minutes, since wind turbines do not have

standard rating methodology. high inertia.

An additional increase of the transmission-line capacity As another important precaution, the types of rating in­­

was then evaluated. The new allowed limit, designated as creases presented here cannot be generally assumed. Ambi-

conditional capacity level 2, was 1,860 A/phase or 930 A/ ent conditions may vary significantly over longer lines and

subconductor. A few exceptions to higher ratings were noted irregular terrains, causing different conductor temperatures at

during delays between the current increase and the higher speed different points along the line.

winds at the conductors’ height. This caused the tempera- There are two very important conclusions resulting from

ture of the conductors to increase at a high rate, which was the analyses developed during this article. The first is that the

an issue of concern. A very careful analysis of available data combination of modeling, analysis, and real-time monitoring

showed that, in some cases, the conductor temperature was very of line conductors and ambient conditions has the potential

close to the safety design temperature limit. to increase current limits of transmission lines connecting

After the definition of the condi-

tional capacity level 2 limit and the

installation of more wind genera- 2,000
tors, there was an increase in wind-

power generation, and the line 1,800
operated frequently at the higher

limit. The temperature of the con- Ampere/Phase 1,600 1,110-MWh
ductors never violated the tempera- 1,400 Effective
ture design and, hence, maintained Increase

safe distances to ground. 1,200
Operating at higher currents in the

line allowed the transmission of more 1,000
energy to the national network and

avoided the undesirable curtailment 800
of renewable generation. Figure 10

shows the results of a specific day 600

when it was possible to generate and 00
deliver an additional 1,100 MWh. 01
Between October 2014 and August 02
2015, the average daily increase was 03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23

Hour Conditional 01: 1,706 A (+34.9%)
Measured Current
Design Current: 1,262 A
Conditional 02: 1,860 A (+47.0%)

approximately 1,000 MWh, with the

best day up to 1,600 MWh. figure 10. A snapshot of current measurement from 1 May 2015.

march/april 2020 ieee power & energy magazine 39

wind-power plants. The high correlation between genera- capacity, aiming to increase efficiency in the operation of the
tion, line current, and high wind velocities may allow for this lines through innovative technologies. In this context, laboratory
increase while still maintaining safety criteria. tests on ACSRs were analyzed to clarify the interaction between
EM and thermal phenomena, mainly under high-current con-
On the other hand, however, some situations require careful ditions. The characterization of those interacting phenomena
attention to avoid violation of safety limits. The first is the non- quantifies economic and security aspects of cable operation, that
uniformity of land characteristics, where variations in ambient is, joule losses and cable lifespan, and provides more accurate
conditions may result in corresponding variations in conductor calculation of technical cable properties, that is, ac resistance.
temperature, even in high-wind generation scenarios. Also, the
characteristic dynamics of wind generation, as discussed, with The experimental tests were divided in two parts. First,
electrical and ambient phenomena responding to different time we briefly describe the experimental procedure to measure
constants may lead to gaps in the stabilization of conductor the current density of the three aluminum layers, as shown
temperature with risks of violating safety limits. in Figure 11(a) and (b). It basically consists of the insertion
of tubular current sensors in each of its 54 aluminum con-
Finally, an increase in the application of real-time line ductor wires, through the installation of six tubular-profile
monitoring combined with a thorough analysis of monitored spacer structures (a pair by layer), made of phenolic paper, as
data and an evolution of line models shows considerable can be seen in Figure 11(a). The arrangement was specially
promise as a way of increasing the capacities of transmission designed to keep the maximum cable length undisturbed and
lines. This can be extremely valuable in situations of licens- obtain direct measurement of the current in each aluminum
ing and financial restrictions. wire simultaneously.

Research in EM and Thermal A second stage of experimental tests involved measure-
Behaviors of Conductors ment of the transient internal temperatures of the cable at
three radial positions [see Figure 11(d)] by using thermocou-
The optimization of electric energy transmission requires ples embedded in the cable during its manufacturing process,
advanced technical studies that maximize the current-carrying

(a) (b)

Internal T2 T3
Thermocouples T1

Steel Core

(c) (d)

figure 11. The R&D for EM and temperature behaviors of ACSRs. (a) The EM monitoring in individual wires. (b) The labo-
ratory setup for EM measurements. (c) The laboratory setup for thermal measurements. (d) The detail of the internal layer
sensor. (Source: CEPEL; used with permission.)

40 ieee power & energy magazine march/april 2020

as depicted in Figure 11(c) and (d), in which T1 denotes the The measurements also demonstrate how the temperature
thermocouple between the steel core and the first layer of gradient affects the current density distribution once the steady-
conductor wires, while T2 and T3 denote the thermocouples state temperature is achieved.
between the other layers of conductor wires [see Figure 11(d)].
Thermocouples are traditionally installed in holes radially The measurements show the increase in current density
drilled in the cable after its manufacture. However, the nov- concentration in the middle layer with total current value,
elty of this experimental procedure is that the thermocouples’ due to the transformer effect, as illustrated in Figure 12(a)
wires were wound together with the conductor layers, provid- and (b). This EM behavior has significant influence on the
ing more accurate and reliable temperature measurements. transient temperature distribution. Figure 12(c) shows the
temperature measurements of thermocouples T1, T2, and T3
ACSR is the most common conductor used in Brazilian when a high current was suddenly raised from 350 to 2000 A.
transmission lines. The presence of the steel core causes a After 2 min at 2,000 A, the current was again reduced to
redistribution of the current density in the aluminum layers, 350 A. An enlargement of this figure during the period when
known as the transformer effect. The experimental results the temperature variations were greater is presented in Fig-
show how this current redistribution affects the radial tem- ure 12(d), which reveals a very interesting effect resulting
perature distribution at the beginning of the thermal process. from the nonuniform current density in the conductor region.

4 Inner Layer 1,200 A Middle Layer
Middle Layer 4.2
Outer Layer

Current Density (A /mm2) 3.5 1,000 A Current Density (A /mm2) 4 Outer Layer

3 Inner
800 A 3.8 Layer

2.5 3.6

2,000 4,000 6,000 0 10 20 30 40 50
Time (s) Conducting Wire
80
(a) 70 (b)
60
70 T1 T1
T2 T2
T3
T3
60
Temperature (°C) Temperature (°C) 50
50

40

30 5,000 10,000 15,000 20,000 40 14,300 14,400
0 Time (s) 14,200 Time (s)

(c) (d)

figure 12. The EM and thermal results from ACSR conductor tests. (a) The current density in the three conductor layers.
(b) The current density in each of the 54 conductors with 1,200 A. (c) The temperature rise when a high current is applied.
(d) The distribution of radial temperature [detail from (c)].

march/april 2020 ieee power & energy magazine 41

The general assumption that high-generation periods
are necessarily associated with high wind velocities
must be properly verified in practice.

In Figure 12(d), the highest temperatures are generally for For Further Reading
thermocouple T2, which is between the internal and middle
conductor layers. J. C. Salari, “Optimization of bundle geometry in transmis-
sion lines (in Portuguese),” M. Sc. thesis, COPPE/UFRJ, Rio
One of the major findings from the EM measurements de Janeiro, Brazil, Apr. 1993.
is the redistribution of current between the inner and outer
layers [see Figure 12(a)] after the steady-state temperature F. C. Dart, C. K. C. Arruda, R. W. Garcia, and O. Regis,
is achieved. As an effect of the radial temperature gradient, Jr., “High capacity AC transmission lines—The Brazilian
which is relevant for higher currents, the increase of the elec- experience,” in Proc. Cigré/IEC Symp., Cape Town, South
trical resistance of the inner layer tends to be higher than that Africa, 2015, pp. 1–8.
of the outer layer. This causes the current density in the inner
layer to decrease and to increase in the outer layer, as shown in F. M. A. Salas, H. R. B. Orlande, and L. A. M. C. Domingues,
Figure 12(a) for the cases in which the total current applied is “Parameter estimation in heat transfer through an overhead
higher than 800 A. power cable by using the Markov chain Monte Carlo method,”
High Temp. High Press. J., vol. 44, no. 4, pp. 317–336, 2015.
Thermal and EM characterizations of experimental mea-
surements are very useful for improving mathematical mod- J. S. Barrett, O. Nigol, C. J. Fehervari, and R. D. Findlay,
els for line conductors under atypical operational conditions. “A new model of AC resistance in ACSR conductors,” IEEE
In particular, sophisticated simulation models are important Trans. Power Del., vol. 1, no. 2, pp. 198–208, Apr. 1986. doi:
when considering new technologies designed to the increase 10.1109/TPWRD.1986.4307951.
the current capacity, that is, DLR. In this scenario, the mea-
surements can support a more accurate prediction of the O. Régis, Jr and L. A. M. C. Domingues, “Increasing the
thermal and electrical behaviors of the conductors. As the transfer capacity of overhead lines on the connection of wind
measurements also showed, steel core cables need special power plants, through correlation between climatic data and
attention when high currents are applied. The transformer temperature of conductors at higher currents,” in Proc. Cigré
effect states that, with an odd number of aluminum layers, Session, Paris, France, Ref. B2-102, pp. 1–9, 2016.
the resulting alternating longitudinal magnetic flux in the
steel core is significant and causes power loss, due to hys- S. Uski-Joutsenvuo and R. Pasonen, “Maximising power
teresis and eddy currents, and a redistribution of the current line transmission capability by employing dynamic line rat-
density in the aluminum layers, as verified by the experimen- ings—Technical survey and applicability in Finland,” Res.
tal results. Rep., VTT, Espoo, Finland, 2013. [Online]. Available: http://
sgem f i n a l r e p o r t .f i / f i le s / D5.1. 55%2 0 -%2 0 D y n a m ic%2 0
However, some design features could reduce the impact line%20rating.pdf
of the increasing ac resistance due to the transformer effect.
For instance, a greater cross-sectional area of the middle L. E. Reis and J. C. Salari, “A methodology for insula-
layer or even avoiding conductors with an odd number of tion coordination for overhead transmission line design,” in
aluminum layers could be used. An even number of alu- Proc. XIV SEPOPE, Recife, Brazil, Sept. 2018.
minum layers partially or totally cancels the magnetic field
in the steel core. Likewise, for the construction of new M. Ghassemi, “High surge impedance loading (HSIL)
transmission lines, the implications of the presence of the lines: A review identifying opportunities, challenges, and fu-
steel core should be considered, especially for conductors ture research needs,” IEEE Trans. Power Del., vol. 34, no. 5,
designed to operate at high temperatures without losing pp. 1909–1924, 2019. doi: 10.1109/TPWRD.2019.2910210.
their mechanical properties, that is, conductors with high
current-carrying capacity, such as the aluminum conductor Biographies
steel-supported conductor.
Carlos Kleber Arruda is with Centro de Pesquisas de Ener-
Acknowledgments
gia Elétrica, Rio de Janeiro, Brazil.
We acknowledge the Companhia Elétrica do Rio São Fran-
cisco and Furnas Centrais Elétricas, original supporters of Luís Adriano M.C. Domingues is with Centro de Pes-
the high SIL R&D.
quisas de Energia Elétrica, Rio de Janeiro, Brazil.

Arthur Linhares Esteves dos Reis is with Centro de Pes-

quisas de Energia Elétrica, Rio de Janeiro, Brazil.

Farith Mustafa Absi Salas is with Centro de Pesquisas

de Energia Elétrica, Rio de Janeiro, Brazil.

João Clavio Salari is with Centro de Pesquisas de Ener-

gia Elétrica, Rio de Janeiro, Brazil. p&e


42 ieee power & energy magazine march/april 2020

By Bruno Meyer, Jean-Yves Astic, Pierre Meyer,
François-Xavier Sardou, Christian Poumarede,
Nicolas Couturier, Mathieu Fontaine, Christian Lemaitre,

Jean Maeght, and Clémentine Straub

Power Transmission
Technologies
and Solutions

The Latest
Advances at
RTE, the French
Transmission
System Operator

©ISTOCKPHOTO.COM/DRMAKKOY RRTE IS THE FRENCH TRANSMIS-
sion system operator (TSO) that owns,
Digital Object Identifier 10.1109/MPE.2019.2959053 develops, maintains, and operates a pow-
Date of current version: 19 February 2020 er grid serving a load of 460 TWh, with
100,000 km of lines and cables and 2,700
march/april 2020 substations of 63, 90, 225, and 400 kV. As is
the case with many TSOs, the company plays a
major role in enabling the successful transition to
a system that can integrate more intermittent renew-
able resources and facilitate the development of smart
grids and microgrids. With the increasing difficulty of
building new lines and substations, the company strives to
make the best use of its existing assets and improve the sustain-
ability of new designs and components installed on the grid. R&D
and innovation, new technology, telecommunications, and compu-
tation play key roles in the future development of the grid.

1540-7977/20©2020IEEE ieee power & energy magazine 43

The solutions are part of the corporate strategic objective to be at
the forefront of eco-design, which aims to reduce the company’s
global environmental footprint.

This article presents some of the latest innovations that Main Use Cases Identified and First Results
have been put into operation and are about to be implemented.
The solutions are part of the corporate strategic objective to Ski Resort Supplied by Two OHLs
be at the forefront of eco-design, which aims to reduce the With Low Static Ratings
company’s global environmental footprint. This includes the During winter, the demand for electricity at ski resorts in the
consideration of greenhouse-gas emissions, the use of raw French Alps increases to the extent that some of the transmis-
materials, and the impact on biodiversity. Eco-design can be sion lines operate at or very close to their static limits. One
considered at a grid level that fully utilizes existing assets to solution to this problem would be to build a new transmis-
limit the unnecessary development of new infrastructure and sion line. An option to avoid such a significant investment is
in the design of grid-related equipment. to use DLRs and operate the transmission line closer to its
true limit. Indeed, the high load demand in winter correlates
Increasing the power-flow capability of the existing trans- with low ambient temperatures. Moreover, the conductor’s
mission system must recognize that the system should be exposure to the wind chill at this time would also increase
secure at all times under N-1 criteria. Operating near the real the maximum current-carrying capability of the line above
maximum circuit ampacity can be achieved by monitoring its static rating, which is based on more conservative ambi-
weather conditions and utilizing dynamic line ratings (DLRs) ent assumptions.
for overhead lines (OHLs). Underground-cable designs with
embedded optical fibers that sense conductor temperatures can From 2013 to 2017, one OHL in the French Alps was
be used to establish ratings and monitor the line’s conditions, equipped with DLR sensors to confirm the theoretical appli-
which reduces the number of outages. Another way to increase cation of this technology. Based on the static-rating value, dur-
the power flow uses adaptive and flexible electronic devices ing periods of low winter temperatures, operators must change
(SmartModules). The last example in this category presents the the network topology and feed the substation with a single line
use of battery energy storage at the subtransmission level to to comply with the N-1 criteria. Since the area is exposed to
reduce potential local congestion, particularly the excess flows power outages from faults on a nearby line, a new underground
that result from local renewable generation. The development line was installed in 2017. Before the new line was commis-
and installation of a sulfur hexafluoride (SF6)-free substation sioned, the use of dynamic ratings enabled the operators to
provides a means of decreasing use of one of the worst green- avoid changing the grid topology, which could have detrimen-
house gases in terms of its global warming potential (GWP). tally impacted reliability for approximately 200 h/year.

DLRs for OHLs Delivery of Electricity Generated by Wind Farms
In France, wind turbines are usually built in rural areas,
Electrical and mechanical constraints limit the permissible away from inhabited locations where the electrical grid is
power flows across OHLs. Historically, operators employed more developed (meshed, with lines that have high static rat-
a static rating based on unfavorable weather conditions to ings). Thus, the aggregation of the wind turbines may require
ensure that conductor temperatures remained within design the addition of new lines to enable the delivery of all of the
specifications. DLRs can be established by monitoring real- electricity produced. Wind speed is one of the most influen-
time meteorological parameters, such as wind speed, ambient tial factors for cooling conductors. The times when line cur-
temperature, and solar radiation. Applying DLR technology rents are very high coincide with periods when wind power
helps to fully utilize the potential of existing OHLs. generation is at its peak, meaning that, at the same moment,
wind is blowing on the conductors to help cool them. This
Since 2009, different DLR applications have been tested suggests that DLR applications may avoid a major capital
to determine the potential use of this technology. Several investment in new transmission lines.
trial installations were implemented to
Since the beginning of 2018, two OHLs have been moni-
✔✔ estimate the benefits offered by DLRs compared to tored as use cases: one at 63 kV and another at 90 kV. Based
static ratings for all use cases on a one-year analysis, the use of dynamic ratings provided
an additional 50% wind-power capacity connection. Indeed,
✔✔ resolve the main operational issues: without DLRs, connecting wind power plants would have
• deciding when to implement DLRs on an OHL been infeasible due to insufficient transmission capacity.
• equipping an OHL with a DLR
• using DLRs in operations
• determining what maintenance is necessary.

44 ieee power & energy magazine march/april 2020

A specific use case has been identified for a strategic or parallel to the wind direction, are highlighted through
400-kV OHL that supplies the southwest of France. A failure these outputs.
on another 400-kV line may cause an overload and lead to
a supply interruption for the whole area. Under those con- Research Project on a Weather-Based Model
ditions, operators must start local thermal power plants to Figure 1 shows weather-data acquisition equipment and line
avoid the potential for a blackout. Since the costs associated sensors that were fitted to an OHL test installation. The
with this action can add up quickly, DLR implementation was measurements provided data on
used to prevent them. The strategic line is often exposed to
high and steady wind speeds, offering a better ampacity than ✔✔ the ambient temperature, wind speed and direction,
its standard static rating. Within two years, the money saved and solar radiation
from redispatching the thermal power plants covered the cost
of the DLR system. ✔✔ the span’s sag, or ground clearance
✔✔ conductor temperatures.
Determining Critical Spans The project’s main objectives are to develop a weather-
and Identifying Future DLR Benefits based DLR using accurate parameters. The model computes
The process of deciding to equip an OHL with DLRs can be the transient capacity by analyzing the conductor’s dynamic
divided into two steps. First, it is necessary to evaluate the thermal behavior. It also creates a forecast model that meets
benefits offered by DLRs compared to static ratings. Sec- operators’ needs by calculating the ratings as a function of
ond, the cost of the project can be estimated after choos- time. The calculation provides a comparison of the DLR
ing the location of the spans to equip with sensors, enabling and static ratings based on the conductor’s temperature,
a cost-benefit assessment. Software has been developed which is determined from ambient conditions using IEEE
to perform these actions. The inputs consist of historical and International Council on Large Electric Systems meth-
weather data with high spatial resolution and the character- ods, with a focus on high-wind conditions. The project will
istics of the line (the type of conductor, maximum conductor compare the calculations with actual line measurements.
temperature, line profile, and so on). The outputs are DLR The first results from the test installation were expected by
values for each span of the line as a function of time for all the beginning of 2020.
of the historical data. This facilitates the evaluation of DLR
benefits for given spans. Digitizing OLs: Specific Challenges
The previously described DLR use cases suggest that two
From these outputs, the line’s ampacity for each time specific technical limitations should be overcome to enable
period can be deduced as the minimal value of all of the the scaling-up of smart solutions.
spans. The benefits of increasing the dynamic ampacity are
analyzed using statistical studies compared to the cost of the Wireless Telecommunications
equipment to decide if DLRs should be installed. Moreover, Until approximately 2016, the only available technologies to
critical spans, which are shielded from the prevailing wind set up monitoring experiments that required wireless commu-
nication were 2G (machine-to-machine solutions) or 3G and

figure 1. The sensor installation on the OHL for the DLR laboratory. (Source: RTE; used with permission.)

march/april 2020 ieee power & energy magazine 45

Another way to improve grid operation is to reduce the asset
downtime that results from failures (with a duration of days to weeks)
and periodic maintenance actions that require de-energization.

4G (for use cases requiring a broader bandwidth). Powering However, today’s microprocessors and microcontrollers need,
those systems generally required batteries whose lifespan was at most, a few watts to provide IoT connectivity and embedded
only a few months. Adding energy-harvesting solutions such intelligence. RTE’s R&D Department works with its partners
as solar panels enhanced the systems’ lifespan, but placing to design solutions that are easy to install, maintain, and use,
those devices on a tower risked affecting the structure’s integ- while having the least possible adverse impact on the tower
rity by adding weight, size, wind resistance, and additional structures. These solutions will supply the few watts needed by
maintenance requirements. smart devices to sense and communicate on IoT networks and
be part of the so-called fog and edge computing of the TSO.
Then appeared Internet of Things (IoT) solutions, promis-
ing to break this technological lock. In 2017, a two-year “sand- RTE’s First Super-Digital
box” project was initiated to facilitate the experimentation of Underground Link
monitoring use cases incorporating IoT solutions: in reference
to the place where little children safely learn how to play and In a fashion similar to OHLs, underground links can ensure
walk, the sandbox is a place and an organization that allows greater flexibility for grid operation. The historical way by
for safe testing, failing, retrying, and thus learning. which the company rates capacity for underground cable
systems assumes continuous loading at full capacity and
The evaluations addressed the technical and value chain establishes the resulting impact on the cable temperature.
from the connected object to the business use by visualizing However, the main difference between overhead and under-
and correlating the data that were generated. The conclu- ground circuits is thermal inertia. It could take up to sev-
sions provided by the project helped design the company’s eral weeks for a cable to reach its steady-state temperature
industrialized architecture and methods for IoT. after applying a load step, depending on soil characteristics,
whereas an OHL requires no more than half an hour.
Powering Equipment Installed on OHL Towers
Electric transmission system towers are widely spread throughout From a TSO perspective, operating at maximum capacity
the country. Monitoring them and their environment, or using for long periods rarely occurs. In particular, operators need to
them to support smart systems, might provide opportunities respect the N-1 criteria, which concern the ability to endure
for efficiencies, for instance, in maintenance planning. But the a loading increase due to the outage of other equipment. The
energy to power smart devices is not easily available on towers. result of this security rule is that many power circuits may
never reach such heavy-loading situations. The steady-state
Topsoil loading hypothesis for cable ratings usually included conserva-
tive assumptions about the impactful parameters’ values, such
Backfill as ambient temperature and soil thermal resistivity. These con-
siderations may lead to oversized conductors and unnecessary
1.5 m Warning Net extra costs.

HDPE Duct HDPE Duct Real-Time Data Requirement
for Earth- for Optical- To optimize the modeling required to operate a cable closer to
Continuity Fiber Cable its physical rating, real-time knowledge of the cable’s surround-
Conductor ings and loading is required. A common way to obtain this
HDPE Ducts information is by using distributed temperature sensor (DTS)
Power for Power measurements. By using an optical fiber, a DTS can measure
Cables Cables the temperature in tens of minutes, along tens of kilometers,
with an accuracy near 1 °C and a spatial resolution close to 1 m.
0.5 m
For the past 20 years, optical-fiber cables were system-
figure 2. The solution when the fiber-optic cable is atically installed in dedicated ducts placed in parallel to all
inserted in separate ducts close to the three-phase power new underground power lines (Figure 2). Intended for com-
cables. HDPE: high-density polyethylene. munication and protection purposes, the optical fibers can
also be used for thermal monitoring. The goal is simple.
By knowing the fiber’s temperature in real time, one can

46 ieee power & energy magazine march/april 2020

estimate the power cable’s core temperature and compute ✔✔ a DTS measuring the temperature along external and
the ampacity of the link. embedded optical fibers and enabling the RTTR

The idea is worth examining, but the implementation is ✔✔ a distributed acoustic sensor (DAS) that monitors the
actually not that straightforward. If the external optical-fiber sound near the optical fiber
cable is perfectly located for maintenance applications—
detection of changes of surrounding conditions, unknown ✔✔ several partial-discharge (PD) sensors to detect small
heat-source crossings, drying out soils, and so on—it would be dielectric breakdowns inside high-voltage (HV)
too far from the power cables to accurately capture dynamic components
temperature changes. Therefore, this configuration is not
sufficient to implement an effective real-time thermal rating ✔✔ numerous Rogowski coils for sheath-current mea-
(RTTR) function. surement.

The challenge is to install sensors as close as possible to By monitoring the root causes of major failures, the
the conductor by integrating optical fibers directly inside implementation of condition-based and predictive-main-
power cables. This should provide quicker and more pre- tenance practices seems possible. This new demonstration
cise temperature measurements, which will form the basis project is designed to maximize the underground-link avail-
of an efficient RTTR solution. To confirm the concept, three ability and take full advantage of the link’s current rating for
power cables in a new underground link will be equipped a smarter asset-management strategy.
with embedded optical fibers (Figure 3). This pilot project
will determine whether embedded fibers make it possible
to obtain sufficient temperature-variation measurements and,
thus, an effective RTTR system. As a means of comparing
temperature variations, the external optical-fiber cable will
also be monitored.

Experiment for Global figure 3. The cable cross-section representation displaying
Asset-Management Improvement two optical modules (in red) that have eight optical fibers
Another way to improve grid operation is to reduce the asset each. (Source: Prysmian Group; used with permission.)
downtime that results from failures (with a duration of days
to weeks) and periodic maintenance actions that require de-
energization (lasting hours to days). To that end, various moni-
toring devices have been installed on a circuit to assess the
equipment-aging process, estimate the state of equipment in
real time, improve maintenance practices, avoid major fail-
ures, and optimize repair work when failures do occur. These
monitoring solutions are anticipated to prevent most of the
main causes of failure (Table 1). In total, more than 20 devices
have been deployed:

table 1. The value of each monitoring device.

Failure Root Cause Example Monitoring Principle Benefits
Material Solution Identification
defects during of defects from
manufacturing or Small imperfections in insulation PD sensors Detection and localization the start, during
mounting producing partial discharges and Rogowski coils of electrical activity warranty period
Third-party damage premature aging Detection of circulating
Surrounding Jacket damage during pulling that induced current Safety and integrity
changes creates a second grounding point of the link
Ampacity-reliability
Grounding failures Undeclared civil works DAS Detection, identification, assurance
and localization of hazards
Cable-protection-
Unknown heat-source crossing DTS Detection and localization reliability assurance
Soil dry-out RTTR of the cause for removal
Detection of ampacity
deviation

Sheath-voltage limiter failure Rogowski coils Detection of circulating
induced current

march/april 2020 ieee power & energy magazine 47

Before 105%
32%
Overloaded Line and
Unused Spare Capacity 21%
on Parallel Lines

After (a) +50 MW

Power Pushed to 99%
Unused Parallel Lines, 48%
Resolving Overload 34%

(b)

figure 4. Adding SmartModules can increase the flow of a particular OHL: (a) before adding SmartModules and (b) after
adding SmartModules. (Source: Smart Wires; used with permission.)

Power Line Devices to Control OHL Power Flow:
SmartModules
XM Power
Supply By design, all OHLs are limited by electrical and mechani-
S1 cal constraints and sized to meet initial and forecast needs.
S2 However, the system’s power-flow needs could change dur-
ing a line’s lifetime. Operators can face situations where
Communications Control one link is overloaded while other links have spare capacity.
(a) During the long term, several questions need to be answered.
How do we increase the efficiency of grid operations? How
(b) do we decide on the most economical new investments that
will flexibly reduce congestion, given greater uncertainty
figure 5. The (a) detailed electrical scheme of (b) the about future flows on the network? The application of
smart-module devices. (Source: Smart Wires; used power-flow control devices could provide answers under a
with permission.) wide variety of system conditions.

48 ieee power & energy magazine New Devices for
Power-Flow Control Solutions

The use of flexible ac transmission systems (FACTSs), such as
fixed series, static var, static synchronous, and static synchro-
nous series compensators, provide control of ac transmission
system parameters to increase power-transfer capabilities,
but, until now, most FACTS devices were installed mainly
to address stability and voltage issues. To date, the deploy-
ment of FACTS devices in France has been limited due to
the equipment’s high cost and large footprint and the lower
anticipated need for resolving voltage and stability issues.

Distributed FACTS devices control power flows to solve
network issues (Figure 4). These devices, called Smart-
Modules (in this case, using FACTS technology developed
by Smart Wires), adjust the transmission system transfer
capacity by increasing the link’s impedance, thus redirect-
ing flows toward less constrained lines. The number of
installed modules depends on the necessary modulation
level and the line’s current rating (Figure 5). SmartModules

march/april 2020