were installed on the 63-kV grid in southwestern France as the flows on the lines. The devices have been deployed on
a research project. The system used a Wi-Fi communica- line conductors at 63 kV in the demonstration project, but
tion system between the onsite modules and a 3G network installations of up to 400 kV are possible. The installed proj-
linking the site to a web-hosted platform installed in RTE’s ect utilizes “push-mode” regulation, which increases the
regional control centers. line’s impedance.
Directed by a dispatcher in a control center, commands New power-flow modulation FACTS devices use a simi-
are sent to a master controller that has the desired level of lar compact-technology approach. They can be installed in
impedance injection. Several operating modes can be selected substations and offer push and pull operation modes (by
to reach maximum flexibility: increasing or decreasing the impedance of the circuit). Com-
pared to series reactors and phase-shifting transformers,
1) a fixed predefined current threshold for automatic im- the new FACTS equipment promises an improved flexible
pedance injection operation and is the economic choice for some applications
that require medium-size flow modulation.
2) an operator-selected predefined response for differ-
ent automatic impedance injections based on the line Large Batteries for Grid Purposes
loading
Subtransmission Grid Areas
3) direct manual commands from the dispatcher to inject With Renewable-Generation Congestion
impedances. An increasing number of 63- and 90-kV subtransmission
areas are or will be congested in the near future due to
For instance, it is possible to program all of the modules to large volumes of renewable generation. This is not by acci-
inject impedances when the current level reaches 600 A and dent; during the past 10 years, negotiations among regula-
have a scalability programmed scenario where 30% of the tory authorities, utilities, and energy-industry stakeholders
modules inject impedance when currents reach 300 A, while led to many regional renewable-energy development plans.
another 30% make injections when currents reach 500 A and The plans facilitated grid development through shared costs
so on. Alternatively, the operator can exercise complete con- among new generation owners, in particular the new play-
trol over the number of injected modules. ers in renewable energy. That led to a belief, widely shared
among stakeholders in France, that the grid-expansion plans
A Demonstration Project in Operation would be too expensive to accommodate 100% of the renew-
After tests conducted in 2017, RTE installed a demonstra- able generators’ nominal power. Thus, it was decided to
tion line in 2018 with 102 SmartModules (34 per phase) on size the overall grid to accommodate 70% of the renewable
the Dantou–Villeneuve 63-kV circuit in southern France to sources’ nominal power ratings. This may lead to localized
resolve post-contingency overload situations. The system renewable-generation curtailment when all of the renewable
has the ability to modulate approximately 10% of the total generation in a relatively small area is producing close to
line impedance. 100% of its nominal capacities.
Line power-flow control management leads to optimized
grid usage in real time and represents a flexible solution to
local uncertainty. The SmartModules shown in Figure 6 offer
several potential economic benefits through their operational
flexibility, possible reuse and relocation, and
low initial capital-expenditure investment
that provides easily scalable solutions if sys-
tem needs change in the future. The installa-
tion requires a short line outage; when heli-
copters are used, the work can be completed
in fewer than 10 min per module. SmartMod-
ules are designed to last for at least 20 years
(including the controls and power electronics)
with limited preventative maintenance (visual
evaluations during normal line inspections at
least every five years) and, if needed, repairs.
Applications and Next Steps figure 6. SmartModules installed on a transmission line. (Source: RTE; used
A solution is available for grid planners to with permission.)
resolve overloads and rapidly adapt the net-
work by redirecting the power flow instead of
building new lines. Similar to the DLR solu-
tions, SmartModules are a way to develop
flexibility in grid operation by influencing
march/april 2020 ieee power & energy magazine 49
Battery Energy Storage as a Grid Component pute capacity bandwidths for each battery, which will fore-
Plans call for installing three energy-storage systems with cast security domains (in power and energy). Operating the
large batteries. The size of each battery system will be 12 MW batteries within those bandwidths ensures that they will be
(the power rating) and 24 MWh (the energy rating). The bat- able to optimally manage congestion without creating any
teries will be connected to the 63-kV grid in two locations new excess.
and to the 90-kV grid in one location. All three projects
are expected to be in operation by the end of 2020. They Real-Time Controller: Area Slow Controls
were designed for two main applications. First, they can In each zone, an area slow control real-time controller
act quickly (0–12 MW in 1 s) and be used for fast remedial will be deployed based on distributed implementation.
actions. After a fault or an outage, if there is an overload on This c losed-loop control receives measurements of the grid
a line, the battery will start charging (because it is upstream flows every second. Every 5 s it computes actions to be sent
of the overload), and the overload will be removed rapidly. automatically to controlled devices: battery installations to
The second application is more energy oriented. Under con- charge or discharge, renewable-generation curtailment for
ditions when renewable-energy generation is very high (pos- each substation in the managed area, switch opening for
sibly resulting in congestion), the battery will store energy. node splitting, and, in some cases, line opening. The math-
The stored energy will be discharged when the renewable ematical framework uses model predictive control with
generation declines and there is no congestion in the local embedded dc linear modeling and optimization.
sub-transmission system.
Last Resort: Substation Fast Controls
Simulations for Optimized Localization According to the optimize-control-protect operating scheme,
Large studies were conducted to find the optimal location on fast and purely local controls ensure last-resort protection of
the grid for the three batteries. Beginning with 15 potential equipment and people.
sites, two years of archived hourly grid data were modified
for 2021 conditions and generation profiles. Grid simula- Changing Framework
tions were conducted, and the optimal use of the batteries When no congestion is foreseen in these zones, stakehold-
for congestion management was determined. The total quan- ers in the energy sector could make the batteries available
tity of renewable-generation curtailment was calculated to for other uses. The concept of battery-capacity bandwidths
provide an indication of the batteries’ impact at the possible identifies good candidates for installations that can provide
locations. In conjunction with technical feasibility studies multiple services.
that were conducted in parallel, locations in the Southern
Alps, West Atlantic Coast, and Northeast regions of France Researchers predict that, in the near future, line over-
were chosen. loads will not be based on current ratings (that is, the maxi-
mum value for amperage) but use maximum values for the
Need for Battery and temperature and sag, whatever the amperage value. This will
Generation Curtailment Coordination be possible through real-time sag and temperature measure-
Since the lines are expected to be severely congested in ments and substation fast controls that open lines on the
the three locations that were selected, the batteries, despite basis of the measurements. This method differs from the
their scale, may not have the capacity to fully relieve the DLR performance described previously since it does not rely
strain. As such, some degree of renewable-generation cur- on current measurements and limitations.
tailment is expected. To properly manage and coordinate
the batteries and curtailment, a new controller is being SF6-Free Substation: Next-Generation
developed to perform autonomous congestion management Initiative
in these subtransmission areas; its three levels are pre-
sented next. A Long-Standing Practice Reaches Its Limits
SF6 has been widely used in the electric-power industry for
Higher Level: Centralized Slow Controls 40 years as the best and least expensive material for gas-
In the considered areas, congestion results from large vol- insulated substations (GISs) and circuit breakers. However,
umes of generation. To compensate for the overloads, the SF6 is now recognized for its poor GWP performance when
batteries would need to charge to absorb some of the gen- leaks occur in aging components. The Kyoto protocol listed
eration. Centralized slow controls (CSCs) will run in the it among the six most harmful greenhouse gases. According
control rooms every 5 min to operate each battery. Based to the Greenhouse-Gas Protocol GWP table values (based
on deterministic forecasts, the CSCs will compute the refer- on the 2014 Intergovernmental Panel on Climate Change’s
ence trajectory to ensure that the battery is fully discharged fifth assessment report), SF6 has the strongest GWP com-
when congestion occurs and ready to manage the excess by puted for a 100-year normalized reference period. SF6 is
charging. Using grid simulations, the CSCs will also com- equivalent to 23,500 kg of carbon dioxide (CO2) and has a
lifetime of approximately 3,200 years due to its exceptional
50 ieee power & energy magazine march/april 2020
chemical stability, which was the main property necessary The project was initiated in 2018, and energization was
for arc quenching in circuit breakers. completed in the second quarter of 2019. Maintenance and
operations staff are gathering information that will be exam-
GISs have been designed to have less than a predeter- ined to monitor the equipment’s performance.
mined percentage value of annual structural leakage [as
stated in International Electrotechnical Commission (IEC) Next-Generation Compact Substation
Standard 62271-1 for HV switch and control gear]. However, The Grimaud 63-kV substation is a prototype demonstration
higher leakage rates have been experienced, sometimes up project for validation in an operational environment (Fig-
to 5%, due to aging or ultraviolet-dried joints. Finding leaks ures 7 and 8). However, other concepts for SF6-free 63-kV
in complex, compact GISs is challenging when there are substations have emerged, and there are comparable ideas
low gas flows and too few continuously monitoring sensors for 225- and 400-kV facilities. There is currently no off-the-
on the equipment to provide reference data for comparison. shelf solution for every voltage level employed by the TSO.
The French system consists of approximately 150 SF6 GIS
substations (from 63 to 400 kV) and roughly 12,800 SF6 The requirements that encompass all voltage levels are
circuit breakers. as follows:
However, alternatives to SF6 and new switching-equip- ✔✔ eco-design of the substation with no SF6 gas (or at
ment designs (such as vacuum chambers) are ready for a least a massive reduction in its use)
system prototype test in an operational environment, at
least up to a 132-kV voltage level. They could be considered ✔✔ reduced and compact geographic footprint
for use at a greenfield demonstration project at a 63-kV GIS
substation (Grimaud) in Southern France that incorporates
an alternative gas mixture named g3, which is provided
by General Electric. RTE also launched a European R&D
tender procedure, the Innovation Partnership, to develop a
pilot site to test concepts for its upcoming compact-substa-
tion generation.
Grimaud 63-kV GIS Substation Project figure 7. The Grimaud substation and RTE personnel.
Grimaud is a new 225- and 63-kV substation. All of the (Source: RTE; used with permission.)
225-kV components use a classic SF6 GIS design. How-
ever, a test will be conducted using the recently devel- figure 8. Since SF6 and non-SF6 technologies are used in
oped fluronitrile mixture (NOVEC 4710 + oxygen + CO2) the same substation, the non-SF6 components are painted
instead of SF6 for all of the components (circuit breakers, green, and different sizes are chosen to prevent improper
disconnectors, bus bars, and instrument transformers) in operation by maintenance crews. (Source: General Electric;
the 63-kV substation, which is located in a separate build- used with permission.)
ing. An experiment will be conducted to analyze gas solu-
tions and monitor partial discharges to collect reference
data from the time of installation throughout the life of the
components. New tools to perform equipment maintenance
will also be evaluated.
Since there are two technologies (SF6 and non-SF6) in
the same substation, special devices had to be designed or
adapted to be maintenance friendly.
✔✔ Non-SF6 compartments are painted green.
✔✔ All of the monitoring equipment and associated wires
are purple for immediate identification.
✔✔ Special filling taps and caps with different sizes, shapes,
and colors were designed to avoid gas confusion.
✔✔ Maintenance crews use CO2 and carbon-monoxide
sensors and wear masks with air cartridges (as done
in classic SF6 GISs years ago).
✔✔ A dedicated filling tool for injecting the premixed gas
in the components was purchased.
✔✔ SF6 and non-SF6 spare parts are stored in different lo-
cations to prevent worker confusion (the non-SF6 does
not use the same pressure as the SF6).
march/april 2020 ieee power & energy magazine 51
The article also explained the increasing focus on
environmental concerns and methods for achieving
a strong eco-design approach.
✔✔ highly digitized equipment (compliance with low- ✔✔ Use of large battery energy storage for grid purposes: A
power instrument transformers and the IEC 61850 pilot project will be conducted to validate the use of large-
protocol for the use of sensors to perform monitoring) size batteries that manage intermittent congestion result-
ing from renewable-energy sources. These batteries, locat-
✔✔ easy maintenance. ed in appropriate substations of the grid, will be charged to
RTE began the Innovation Partnership to pursue long- accommodate the peak generation from renewables. The
term research, development, and performance tests and technical challenge is to implement a control system able
acquire pilot sites for applying new concepts and products. to automatically optimize each battery’s state of charge to
Industrial partners will be selected according to their inno- avoid congestion in preventive and curative modes without
vative technologies and abilities to maintain a research and any action from the power-system operators.
sustainable development effort in the HV–extra-HV sub-
station-equipment domain. The research phase will last for ✔✔ SF6-free substations: Widely used for 40 years as the
a maximum of two years. The development and pilot-test best and least expensive insulator gas for GISs and
phase will take no more than three years. circuit breakers, SF6 is now recognized for its impact
on GW when leaks occur in aging components. RTE
Summary commissioned its first 63-kV alternative GIS in 2019
and launched a European innovation-partnership pur-
This article presented a series of innovations at RTE, chasing procedure to design and test other SF6-free
explaining why they were developed, how they were imple- solutions for substations from 63 through 400 kV.
mented, and possible further work to be done. It described
case study solutions where taking advantage of existing grid For Further Reading
capabilities when building new lines proved premature in
some cases, expensive in others, and always difficult. The D. Douglass et al., IEEE Standard for Calculating the Cur-
article also explained the increasing focus on environmen- rent-Temperature Relationship of Bare Overhead Conduc-
tal concerns and methods for achieving a strong eco-design tors, IEEE Standard 738, 2012.
approach. The lessons learned are as follows:
C. Straub, S. Olaru, J. Maeght, and P. Panciatici, “Zonal
✔✔ DLR: These technologies are not new, but to be suc- congestion management mixing large battery storage sys-
cessfully implemented, their introduction requires tems and generation curtailment,” in Proc. 2018 IEEE Conf.
caution and a thorough analysis of conditions. Accu- Control Technology and Applications (CCTA), Copenhagen,
rately measuring wind speeds and temperatures along pp. 988–995.
critical spans in real time enables potential increases of
the maximum permissible capacity for OLs. The same P. Glaubitz et al., “CIGRE position paper on the appli-
idea can be applied to underground cable circuits. cation of SF6 in transmission and distribution networks,”
Electra, vol. 34, no. 274, pp. 34–39, 2014.
✔✔ Digitizing OLs and underground cables: By incorpo-
rating power electronics, sensors, telecommunication J. Y. Astic et al., “Control center designs: New functions
equipment (such as optical fibers and Global System and challenges for the transmission system operator,” IEEE
for Mobile Communications standards), and central- Power Energy Mag., vol. 16, no. 2, pp. 57–66, Mar./Apr.
ized computation, equipment can be operated in the 2018. doi: 10.1109/MPE.2017.2779553.
most efficient way. This is particularly useful when
grid flows are highly variable, possibly because of in- Biographies
termittent renewable-energy sources.
Bruno Meyer is with RTE, Paris, France.
✔✔ SmartModules: These devices, when installed on
OHLs, hold the promise of increasing the overall Jean-Yves Astic is with RTE, Paris, France.
grid’s power-flow capabilities in a smart, flexible, and
economic manner. SmartModules may provide an ef- Pierre Meyer is with RTE, Paris, France.
ficient way to solve congestion issues on particular
circuits by controlling the flow through a mix of grid François-Xavier Sardou is with RTE, Paris, France.
and telecom technology. Their first demonstration
was successful and found to be of great value. Christian Poumarede is with RTE, Paris, France.
Nicolas Couturier is with RTE, Paris, France.
Mathieu Fontaine is with RTE, Paris, France.
Christian Lemaitre is with RTE, Paris, France.
Jean Maeght is with RTE, Paris, France. p&e
Clémentine Straub is with RTE, Paris, France.
52 ieee power & energy magazine march/april 2020
©ISTOCKPHOTO.COM/XIJIAN
By Renchang Dai, Guangyi Liu, and Xing Zhang
Transmission
Technologies and
Implementations
TTHE STATE GRID CORPORATION OF CHINA HAS
Building a Stronger, been deploying ultrahigh-voltage (UHV) ac technology
Smarter Power on a large scale since launching its Strong and Smart Grid
Grid in China plan in 2009. China has 80% of its hydropower genera-
tion in the southwest and 76% of its coal generation in the
Digital Object Identifier 10.1109/MPE.2019.2957623 northwest. However, more than 75% of the country’s
Date of current version: 19 February 2020 energy demand is distributed in the eastern and southern
coastal areas. This geographical mismatch between supply
and demand made it necessary to build UHV transmission
march/april 2020 1540-7977/20©2020IEEE ieee power & energy magazine 53
networks: transmission technologies at voltage levels of 1,000 kV the utility plans to build 10 more UHV ac lines as well as
for ac and ±1,000 kV for dc. In this article, the development UHV dc lines by 2020, raising the total UHV transmission
of UHV transmission-system technologies and projects is capacity to 450 GW.
detailed, with a focus on the UHV ac transmission system.
The First UHV ac Transmission-Line Project
In the Strong and Smart Grid plan, the concept of a strong The first 1,000-kV UHV ac transmission project was the
grid means that UHV systems will serve as the backbone of Southeast Jin–Nanyang–Jingmen line. The single-circuit
the national network to ensure greater reliability and stabil- transmission line (with a length of 640 km) connects the
ity. At the same time, the operation of UHV systems requires Changzhi and Jingmen substations through the Nanyang
addressing technical issues such as reactive power manage- switching station. Each 1000-kV substation was equipped
ment, voltage control, and safety. The development of “smart” with one 3,000-MVA UHV main transformer [consisting of
control and operation technologies is a goal of UHV-system three single-phase 1,000-MVA banks (3 × 1,000 MVA)]. To
deployment. This article describes digital real-time simula- compensate for the charging capacitance, a 960-MVA reactor
tion and energy-management systems (EMS) that model, (Mvar) and 720-Mvar HV shunt reactor were installed on each
simulate, monitor, control, and analyze the large-scale ac/dc side of the Changzhi–Nanyang line segment, while a 720-Mvar
power grids. and 600-Mvar HV shunt reactor were added at each side of the
Nanyang–Jingmen section. At the low-voltage side of the
So far, only a handful of countries have implemented Changzhi and Jingmen stations, 840 Mvar (4 × 210 Mvar) of
UHV transmission systems, and there are very few interna- shunt-capacitor banks and 480 Mvar (2 × 240 Mvar) of shunt-
tional standards to guide their development. The State Grid, reactor banks were installed.
the largest utility in the world, has embarked on a project to
develop UHV ac national and international standards. Best The Southeast Jin–Nanyang–Jingmen project demon-
practices for UHV ac transmission-network deployment strated huge benefits in energy transmission, loss reduction,
and the development of UHV ac standards are presented in and emissions mitigation. From 2009 to 2011, the UHV ac line
this article. transmitted 27.71 TWh of electricity, with losses amounting to
only 1.7%. Of that power, 9.2 TWh was hydroelectric, which
UHV Grid Experiences in China eliminated 9 × 106 tons of carbon-dioxide emissions.
The first 1,000-kV UHV ac endeavor, the Southeast Jin– UHV Overhead Transmission-Line
Nanyang–Jingmen line, was launched as a pilot project in Technologies
January 2009. It was built for a capacity of 3,000 MW and The main components of UHV overhead transmission lines
expanded to 5,000 MW on 29 December 2010 for the next are towers and conductors. UHV towers are designed to
phase of the program. Construction of the Huainan–Shang- meet electrical, mechanical, and economic requirements.
hai UHV ac project began on 27 September 2011 to pro- The most commonly used tower designs for UHV ac trans-
vide 8,000 MW of transmission capacity between Anhui mission-line projects in China are guyed, single circuit self-
and Shanghai. In March 2015, the North Zhejiang–Fuzhou supporting (either the cup- or cat-head type), and double cir-
1,000-kV UHV ac double-circuit line was commissioned, cuit. The type of tower depends on the project requirements.
with 6,800 MW of transmission capacity. Those projects as
well as other UHV ac transmission lines are summarized in 1) Guyed tower: A guyed tower consumes less steel but
Table 1. All of the UHV ac lines in the list are maintained occupies a larger area than a self-supporting one.
and operated by the State Grid. Encouraged by its success,
table 1. The 1,000-kV UHV ac transmission-line projects.
Project Commissioned Circuit Installation Length
Capacity (MW) (km)
640
Southeast Jin–Nanyang–Jingmen pilot January 2009 1,000-kV UHV ac single circuit 3,000 640
Southeast Jin–Nanyang–Jingmen December 2012 1,000-kV UHV ac single circuit 5,000 2 × 647
expansion 2 × 603
2 × 730
Huainan–South Shanghai September 2013 1,000-kV UHV ac double circuit 8,000 2 × 800
2 × 608
North Zhejiang–Fuzhou March 2015 1,000-kV UHV ac double circuit 6,800 2 × 1,049
Xiamen–Shandong July 2016 1,000-kV UHV ac double circuit 9,000
Huainan–North Shanghai November 2016 1,000-kV UHV ac double circuit 10,000
West Inner Mongolia–South Tianjing November 2016 1,000-kV UHV ac double circuit 5,000
Yuheng–Weifang August 2017 1,000-kV UHV ac double circuit 4,000
54 ieee power & energy magazine march/april 2020
Because these towers need guy wires, they are feasible that the icing-flashover voltage is more dependent on the
in plains and hilly areas but not in mountainous ter- length of the string. V-insulators and composite insulators
rain. Guyed towers were chosen often in the past when with ice barriers are recommended.
land-usage costs were lower. The manufacturing cost
of a guyed tower is relatively low. In recent years, Chi- UHV Substation-Equipment Technologies
na’s land-use expense has increased; therefore, the to- The equipment in a 1,000-kV substation includes trans-
tal cost of a guyed tower is becoming higher than that formers; shunt reactors; switchgear such as gas-insulated
of a self-supporting design. As a result, guyed-tower switchgear (GIS) and hybrid GIS; metal-oxide surge arrest-
construction is used less frequently than previously. ers; capacitive voltage transformers; grounding switches;
2) Single-circuit, self-supporting tower: Cup- and cat- post insulators; and low-voltage, reactive-power com-
head towers are typical types of single-circuit-suspen- pensation devices. Except for the associated low-voltage,
sion, self-supporting structures. Cat-head towers are reactive-power compensation devices, all UHV substation
commonly used in narrow line corridors. In wide cor- equipment is difficult to design and manufacture. As part of
ridors, cup-type towers are preferred. For the 1,000-kV the UHV ac transmission project, engineers developed and
Southeast Jin–Nanyang–Jingmen UHV ac project, manufactured the first 1,000-kV/1,000-MVA UHV trans-
both types were used. former and one of the largest UHV shunt reactors in the world.
3) Double-circuit tower: A double-circuit tower has three
or four crossarms to vertically support three-phase con- The rated voltage of the 1,000-kV/1,000-MVA trans-
ductors. This design is used for double-circuit transmis- former is 1,000 kV for the primary winding, 500 kV for
sion lines at all voltage ratings, including 1,000 kV. the secondary winding, and 110 kV for the tertiary wind-
Besides the tower, the conductor accounts for a large por- ing. The low-voltage, reactive-power compensation devices
tion of the price to build a UHV ac overhead line. Constrained are installed on the 110-kV winding. The 110-kV winding
by cost, the conductors are selected to most effectively meet capacity is designed to be higher than the installed capac-
the requirements for the transmission capacity, electromag- ity of the low-voltage reactive power-compensation devices.
netic (EM) environment, mechanical strength, radio inter- For example, the Southeast Jin–Nanyang–Jingmen project
ference, and audible noise. Three types of conductors have requires 840 Mvar of capacitive and 960 Mvar of inductive
been used in UHV ac transmission-line projects for different reactive power compensation, but the rated capacity of the
scenarios. The aluminum conductor steel-reinforced variety tertiary winding is designed for 1,000 MVA. Shunt-reactor
is common. The aluminum-alloy-conductor, steel-reinforced and shunt-capacitor banks are installed in UHV ac substa-
version is employed in icy areas, while aluminum-conduc- tions for voltage control. To avoid resonance, the designs
tor, extra-high-strength, steel-reinforced models are widely call for using less than 100% of the shunt compensation. In
used for long spans, such as river crossings. the Changzhi, Nanyang, and Jingmen substations, the shunt
The strong electric field of the UHV ac transmission line capacitors are rated to provide a compensation of 85–88%.
triggers a corona, resulting in power losses. In addition, the
corona causes EM interference, audible noise, and electrical Smart UHV Grid
corrosion on the surface of the wire, reducing the life of the
transmission line. To suppress the corona, bundled conduc- Smart simulation, control, and operation technology is a
tors are adopted. While 500-kV ac transmission lines use goal of the State Grid’s UHV-system deployment. To facili-
four LGJ-300 or LGJ-400 four-bundle conductors, a 1,000-kV tate large UHV ac-grid planning and design, a digital/analog
ac transmission line adopts eight LGJ-400, LGJ-500, hybrid simulator was developed to model the effect of UHV
LGJ-630 eight-bundle conductors, typically with a 30-mm devices on the UHV grid. A new-generation EMS is under
wire diameter and 40-cm splitting distance. For example, development to model, monitor, and operate the UHV grid
the Southeast Jin–Nanyang–Jingmen line uses eight LGJ- from a control center.
500 wire conductors, and the Huainan–Shanghai line adopts
eight LGJ-630 wire types. Simulation Center
UHV ac transmission lines connect power-generation With the highest number of HVdc projects and the largest
centers in the west and north to load centers in eastern and amount of renewable generation, the State Grid is one of the
southern China. They are built at high altitudes. To ensure most complex power networks in the world, making it diffi-
voltage insulation, the altitude-correction factor is measured cult to simulate, analyze, and control. To improve situational
and applied to adjust the withstand voltage of the external awareness, a simulation center (Figure 1) was built at the
insulation. At high altitudes, the flashover voltage is less China Electric Power Research Institute (CEPRI), Beijing,
than at low altitudes. The effect of altitude on the flashover using state-of-the-art technology. The simulation center
voltage is more dependent on the type of insulator than the houses two systems: a digital–analog hybrid simulator and
length of the string. At high altitudes, icing flashover is an fully digital one.
issue that needs to be addressed. The icing-flash test shows
The digital–analog hybrid consists of a large-scale,
power-system real-time simulator, and, to date, it is the larg-
est of its kind, modeling more than 20 HVdc controls and
march/april 2020 ieee power & energy magazine 55
protection devices, flexible ac transmission-system control to conduct transient-stability (TS), EMT, and TS-EMT
devices, and other power-system elements. With 320 high- hybrid simulations, and the overall efficiency is thousands of
performance CPU cores, the real-time EM transient (EMT) times greater than traditional means. A state–region–prov-
simulation scale exceeds 6,000 three-phase buses, which ince three-layer cloud simulation architecture has been built
could cover any regional power grid in the utility. Real using a supercomputer, and all of the utility’s dispatching
control devices can be connected to the system to per- and control centers and regional and provincial power grids
form digital–analog hybrid simulation, which greatly can remotely access its resources.
enhances accuracy.
The core simulation tool in the center is the Advanced Digi-
The fully digital version is a supercomputer with more tal Power-System Simulator (ADPSS), which was developed
than 24,000 CPU cores specialized for power-system paral- by CEPRI. The ADPSS consists of TS- and EMT-simulation
lel simulation and is one of the most advanced power-system subsystems, and it can perform closed-loop testing via electri-
simulators worldwide. Using a novel multilayer parallel-sim- cal and communication interfaces, as shown in Figure 2. In
ulation scheme, massive simulation cases can be parallelized addition, the ADPSS has online data interfaces that can read
(a) (b)
figure 1. The interior of the State Grid’s simulation center developed by CEPRI uses state-of-the-art technology used for
research to understand system characteristics and improve situational awareness: (a) the supercomputer room and (b) the
supervisory control room. (Source: CEPRI; used with permission.)
SCADA /EMS Console
Data Interface
Electromechanical EM Console
Console
Optical Fiber Optical Fiber
Physical
Physical Interface IEC 61850
Interface Interface
Amplifier Amplifier
GPS
Tested Devices Electromechanical (ST) EM (EMT)
Parallel Tested Devices Tested Devices
figure 2. The ADPSS system architecture. IEC: International Electrotechnical Commission; ST: stability of transient.
56 ieee power & energy magazine march/april 2020
Without fast and accurate calculations, timely responses
to real-time events would be impossible, and reliable
power-system operations would be at risk.
supervisory control and data acquisition (SCADA)/EMS data areas are enabled by UHV transmission, resulting in large
from dispatching systems, and, thus, simulate the system based amounts of power flowing over a wide region. The large and
on practical operating conditions. High-performance comput- complex power network makes it challenging for the EMS
ing with parallel-computing and hardware-in-the-loop tech- to respond quickly to situations. The EMS is evolving to
nology enables system analysts to simulate power systems with address the rapid-response requirements. Without fast and
more than 50,000 nodes and 3,000 generators in real time. accurate calculations, timely responses to real-time events
would be impossible, and reliable power-system operations
In this architecture, relevant physical devices, such as would be at risk.
power converters, protection relays, and automation control-
lers, are connected to the ADPSS through physical interfaces For the next-generation EMS, State Grid engineers are
and/or IEC 61850 interfaces with the digital model of the developing a novel database architecture and fast, parallel
system for an integrated TS and EMS hybrid simulation. The methods to achieve computation cycle times that exceed the
hardware-in-the-loop capability ensures that devices’ high- SCADA sampling rate (Figure 3). An EMS prototype devel-
fidelity characteristics are represented and studied with the oped for installation in a provincial control center processes
whole power system. The simulation center began operating a model of 2,643 buses and 3,185 branches. The key real-
in 2017. Since then, it has systematically improved power- time applications of the EMS include state estimation, power
system simulation accuracy and efficiency for the State Grid flow, and contingency analysis. Those calculations are per-
and been used as a key resource to analyze and study the wide formed significantly faster than with the traditional serial-
range of scenarios and events related to UHV ac/dc transmis- computing-oriented EMS, and all three applications can be
sion projects. completed within a SCADA sampling cycle. The prototype
has been running every 5 s using real SCADA telemetered
EMS data since August 2018. Various execution-time metrics are
The electrical power system is changing into a highly inter- used to compare it with a traditional commercially available
connected, large, and complex network linking conventional EMS, as shown in Tables 2 and 3. A test was conducted on
and renewable-energy sources to load centers via UHV a server unit with two CPUs (six cores × two threads at
transmission lines. Electricity transactions across broad 2.1 GHz). Table 2 compares the performance of the traditional
figure 3. The EMS prototype has a faster-than-SCADA sampling time. WLS: weighted least square; Decoupled P–Q:
active–reactive power-decoupled power flow.
march/april 2020 ieee power & energy magazine 57
calculation methods with the new ones used in the prototype Three IEEE standards relate to UHV ac technologies.
EMS, which are an order of magnitude faster. 1) IEEE Standard 1862-2014, IEEE Recommended Prac-
UHV ac Technical Standards tice for Overvoltage and Insulation Coordination of
Transmission Systems at 1,000 kV ac and Above. This
Building and operating a UHV ac transmission system is pio- standard covers the selection of UHV ac transmis-
neering work. So far, only a few countries have established sion-line and substation insulation-level methods. It
UHV systems in operation. Since there are very limited UHV establishes reliability standards for operating dur-
transmission-line standards to guide system development, the ing overvoltage and lightning overvoltage and recom-
State Grid has encouraged the development of national and mends a calculation method for insulation coordina-
international UHV ac guidelines. The current series includes tion between transmission lines and substations. The
363 corporate, 145 industrial, 66 national, and 19 interna- standard also recommends the overvoltage-control
tional standards. They were established from experience with measures for UHV ac systems of 1,000 kV and above.
UHV ac transmission-line projects. 2) IEEE Standard 1860-2014, IEEE Guide for Volt-
CIGRE established the following working groups (WGs) age Regulation and Reactive Power Compensation
to advance UHV: at 1,000 kV ac and Above. This standard provides
✔✔ WG A3.22: Technical Requirements for Substation voltage control and reactive compensation. It es-
Equipment Exceeding 800 kV tablishes standards and requirements for voltage
✔✔ WG B3.22: Technical Requirements for Substations control and reactive-power compensation to ensure
Exceeding 800 kV system and equipment safety. It is applicable to the
✔✔ WG C4.306: Insulation Coordination of UHV ac planning, design, operation, and research of power
Systems facilities with voltage levels of 1,000 kV and higher.
✔✔ WG A3.28: Switching Phenomena and Testing 3) IEEE Standard 1861-2014, IEEE Guide for On-Site
Requirements for UHV and Extra-HV Equipment Acceptance Tests of Electrical Equipment and System
✔✔ WG B3.29: Field Test Technology on UHV Substation Commissioning of 1,000 kV ac and Above. This stan-
Construction and Operation. dard provides guidance for on-site power-equipment
In 2008, the IEC and CIGRE recommended 1,000 kV acceptance testing. It presents standards and require-
as the standard rated voltage, and the IEC approved it, on ments for test items, conditions, methods, and test
22 May 2009, as the highest voltage for UHV ac equipment. results. This standard describes specifications and
Since 2009, four IEC UHV ac standards have been approved: requirements for acceptance-test field procedures and
1) a specification for 1,000-kV series-compensation equip- commissioning UHV ac-power equipment.
ment for transmission lines, 2) a specification for a 1,000-kV
controllable shunt reactor, 3) a guide related to acceptance Best Practices and Recommendations
testing of 1,000-kV equipment, and 4) a recently approved UHV ac transmission technology is groundbreaking. Besides
standard that applies to on-site acceptance tests of electrical the common issues that challenge ac networks at low volt-
equipment where the highest ac transmission-system voltages age levels, 1,000-kV UHV ac transmission projects face dif-
exceed 800 kV(IEC TS 63042-301:2018, UHV ac Transmis- ficulties related to external insulation characteristics at high
sion Systems—Part 301: On-Site Acceptance Tests). altitudes, in heavy pollution, and during heavy icing. Their
designs must account for overvoltage
table 2. The comparison of the state-estimation execution time (ms). and insulation coordination, the EM
environment, the ability to perform
Method Matrix Factorization RHS F/B live maintenance, and so forth.
Formation Calculation Substitution
For countries that want to incorpo-
Traditional 462.5 338.7 494.8 24.5 rate UHV transmission into their grids,
New 15.7 13.4 48.4 2.5 it is highly recommended to start with
RHS: right-hand side vector; F/B: forward/backward. a pilot project. Knowledge and expe-
rience are important to achieve UHV
ac transmission success. Pilot projects
table 3. The comparison of the power-flow assess the performance and characteris-
execution time (ms). tics of the UHV ac transmission lines,
Method Matrix RHS Branch- substations, equipment, and system, that
Format ion Factorizat ion Calculation F/B Power is, shunt reactors, surge arresters, circuit
Substit ution Calculation breakers, GIS, voltage transformers,
Tradit ional 6.3 80.6 87.7 25.1 3.7 current transformers, and insulators.
14.7 5.4 0.7 1.6 They also offer opportunities to gain
New 5.3 experience in research, manufacturing,
58 ieee power & energy magazine march/april 2020
International standards leverage best practices and
experience by sharing the limitations of and lessons
learned about UHV ac transmission technologies.
operation, and control. Analysis can be performed on field mea- UHV ac transmission lines possess many advantages, pro-
surements of switching, lightning, resonance, and load-shed- viding an effective but expensive solution that incorporates
ding overvoltages; short circuit currents; and capacitor/reactor/ state-of-art technologies in many scenarios. The EM-environ-
line switching operations. The success of a pilot-project builds ment requirements require an enlarged wire space, which in-
experience and confidence to pursue commercial operation of creases the line reactance, necessitating a large shunt-capacitor
additional UHV ac projects. bank for compensation. To suppress the corona, 1,000-kV trans-
mission lines adopt eight-bundle conductors that have a large
Standard equipment is strongly suggested to ensure that wire cross-sectional area. Compared with the four-bundle
technologies and operational experience may be leveraged by conductors for 500-kV transmission lines, 1,000-kV transmis-
multiple UHV ac projects. For example, a 1,000-kV trans- sion lines consume more wire at a higher cost. State-of-the-art
former at the same rating of 3,000/3,000/1,000 MVA is com- generator-insulation levels lag behind the development of UHV
monly used in different UHV ac substations and switching ac transmission-line technology. Voltage-transformation ladders
stations. In the Southeast Jin–Nanyang–Jingmen project, are required to connect a generator to a 1,000kV bus.
the same 720-Mvar, 1,000-kV HV shunt reactor is installed
at each side of the Changzhi–Nanyang and Nanyang– Although crucial milestones in UHV ac transmission
Jingmen line segments. Two HV shunt reactors of a simi- technology and project development have been reached,
lar design with the same voltage rating and Mvar capacity there is still a long way to go. Researchers and engineers are
(720 Mvar) are installed in the Huainan and Anji substations dedicated to improving UHV transmission technologies to
in the Huainan–Shanghai project. Using standard equipment make the power system stronger and smarter.
reduces the required inventory of spare parts and manufac-
turing cost. Operating with standard equipment also enables For Further Reading
utilities to gain more design, installation, maintenance, and
operation experience. Z. Liu, Ultra-High Voltage AC/DC Grids. Waltham, MA:
Academic, 2014.
A digital real-time simulation system with electromechani-
cal transient and EMT-simulation capabilities and test facilities S. Zhusen et al., “Application and dissemination of steel
helps researchers and engineers to understand the character- tubular tower in transmission lines,” Power System Technol.,
istics of UHV ac equipment individually and systematically. vol. 34, no. 6, pp. 186–192, 2010.
The characteristics of UHV ac equipment and systems are not
always well understood. It is difficult to prove that UHV ac G. Li, B. Li, J. Li, and Z. Zhao, “Research and development
equipment will behave in a certain way mathematically, and of UHV AC transformer and shunt reactor,” Eur. Trans. Elect.
it is extremely challenging, if not impossible, to pinpoint all Power, vol. 22, no. 1, pp. 49–59, 2012. doi: 10.1002/etep.559.
parameters through theoretical calculations. Simulation sys-
tems and test facilities are indispensable for UHV ac transmis- X. Wang, B. Jiao, G. Li, Y. Liu, X. Li, and S. Wu, “Devel-
sion-system design, planning, and operation. opment and application of 1000 kV standard voltage trans-
former for field test,” High Voltage Technol., vol. 35, no. 6,
A next-generation EMS with powerful computing per- pp. 1254–1259, 2009.
formance is crucial for a highly interconnected, large, and
complex UHV network. Delayed responses to UHV-network Y. Hu, B. Wan, and H. He, “Key technologies of 1000 kV
contingency events have significant negative impacts on sys- AC compact transmission,” High Voltage Technol., vol. 37,
tem security and stability. Smart situational awareness, fast no. 8, pp. 1825–1831, 2011.
system analysis, and quick control response help to avoid
cascading outages and power blackouts. IEEE Recommended Practice for Overvoltage and Insu-
lation Coordination of Transmission Systems at 1,000 kV
International standards leverage best practices and expe- AC and Above, IEEE Standard 1862, 2014.
rience by sharing the limitations of and lessons learned about
UHV ac transmission technologies. Standards enable effec- Biographies
tive communication for building new UHV ac transmission
projects. After many years of effort by researchers and engi- Renchang Dai is with the Global Energy Interconnection
neers worldwide, several international UHV transmission-
line standards have been established. Research Institute North America, San Jose, California.
Guangyi Liu is with the Global Energy Interconnection
Research Institute North America, San Jose, California.
Xing Zhang is with China Electric Power Research Insti-
tute, Beijing. p&e
march/april 2020 ieee power & energy magazine 59
A Large-
Scale Testbed
as a Virtual
Power Grid
For Closed-Loop Controls
in Research and Testing
By Fangxing Li, Kevin Tomsovic,
and Hantao Cui
TTHE ELECTRIC POWER GRID IS UNDERGOING form should be highly integrated, closed loop, and capable
unprecedented modernization toward higher reliability, of mimicking a real power grid for testing new controls or
higher efficiency, and lower cost through the integration of algorithms. However, traditional software simulation pack-
renewable energy, wide-area monitoring, and advanced con- ages usually perform specific tasks such as dynamic simula-
trol technology. This integration is making the transmission tion or state estimation but lack the capability of providing
grid overwhelmingly complex to understand and model to an integrated closed-loop platform.
apply new control or actuation technologies. This calls for
a fast-prototyping platform for research and testing under In other words, power system researchers often struggle to
the new transmission technology paradigm. Such a plat- obtain realistic data for research under the new transmission
paradigm since they do not own or operate a real power grid.
Digital Object Identifier 10.1109/MPE.2019.2959054 Typically, a researcher in a power system control study will
Date of current version: 19 February 2020 employ a few tools and manually create interactions among
simulation programs and scripts to achieve various goals.
60 ieee power & energy magazine 1540-7977/20©2020IEEE march/april 2020
system is desired as a virtual digital
twin of an actual power grid for power
system research and study. In this way,
research on power system monitoring,
modeling, control, and actuation can
be carried out in a closed-loop inte-
grated environment with high model-
ing fidelity and flexibility.
Researchers have approached such
an integrated environment using one of
two approaches. The first is a loosely
integrated approach of cosimulation
where different software modules are
essentially independent, for example,
the Hierarchical Engine for Large-
scale Infrastructure Co-Simulation.
Such an approach has the advan-
tage of simplifying development and
allows researchers to glue together
sophisticated models without complete
domain knowledge of the underlying
simulators. The disadvantage is that
simply piecing together these modules
may neglect some of the interactions,
and the assumptions across modules
may not be consistent or valid in the
applied domain. The second approach
is to fully integrate the different models
and use sophisticated numerical and
software environments (i.e., the Open
iTesla Power System Library). The
disadvantage is that this requires the
researcher to be familiar with all of the
underlying models or work in larger
teams where all of the needed expertise
is available. Therefore, a compromise
approach is taken using independent
software modules that are restricted to
support a common research objective,
©ISTOCKPHOTO.COM/LEOWOLFERT namely closed-loop, real-time controls.
With this motivation, the large-
scale testbed (LTB) has been devel-
oped by the team at the Center for
For instance, in the scenario of testing real-time transmission Ultra-Wide-Area Resilient Electric Energy Transmission
control algorithms, a dynamic simulation tool will be used to Networks (CURENT), a U.S. National Science Foundation
produce mock measurement data, which will be fed into other (NSF) engineering research center jointly supported by the
software tools as control inputs. Then, the output from such NSF and the U.S. Department of Energy (DoE). This plat-
a control module will be fed back to the dynamic simulator. form aims to be a virtual grid or digital twin of a real power
During this process, either manual efforts or glue scripts are grid such that researchers can obtain simulated yet realistic
required by the researcher to facilitate the closed-loop inter- real-time data or measurements, test control algorithms in
action. To fully test a new approach, one needs to consider real time, and observe grid response to these controllers. It
essential constraints beyond the basic control algorithm, such targets large-scale power grid models of thousands of buses
as communication architecture and bandwidth measurement with new power system components, i.e., wind generators,
performance. Therefore, a fully automated, integrated, and solar photovoltaic panels, energy storage, and multitermi-
closed-loop platform with a comprehensive modeling of the nal high-voltage dc (HVdc) networks. Conventional control
march/april 2020 ieee power & energy magazine 61
The CURENT LTB utilizes distributed software modules
to establish a systemic testing framework where multiple
interoperable software packages work simultaneously.
room functions, including state estimation, contingency tion, monitoring, energy management, and closed-loop control
screening, security assessment, and generation scheduling, capabilities. The CURENT LTB utilizes distributed software
are also integrated as modules, implementing both stan- modules to establish a systemic testing framework where mul-
dard algorithms and research prototypes. Note that in the tiple interoperable software packages work simultaneously to
effort of developing the LTB, existing software packages, represent the online closed-loop power system operation.
both commercial and open source, can be evaluated and
utilized whenever possible to achieve efficiencies. The LTB architecture integrates categories of software
modules using distributed messaging. To characterize the
The main contributions of the LTB as a virtual power modern power systems with physical dynamics and data-
grid for research and testing are as follows: enabled applications, the software pieces are divided into
four categories, as shown in Figure 1. Tools are packaged
✔✔ the design of a decoupled software architecture for as modules with their data interfaces properly defined for
representing the large-scale power system dynamics communication and simultaneous execution. Modules can
and cyber control systems be distributed over multiple processes or computers for par-
allel execution.
✔✔ the development of a distributed messaging environ-
ment for integrating interoperable software modules Simulators, Test Systems, and Scenarios
for simultaneous execution and systematic testing The simulators provide interfaces for querying the
parameter data and streaming time-stamped raw simula-
✔✔ the development of a tool for visualizing the data and tion data. Any simulator can be interfaced with the LTB
interacting with the software modules in runtime. architecture if it provides the program interfaces for
workflow control and data acquisition during runtime.
LTB Architecture for Decoupled Three simulators—ANDES, GridDyn, and OPAL-RT ePHA-
Closed-Loop Testing SORsim—have been integrated with possible extension
A closed-loop testing architecture is proposed for the LTB
to leverage modular software and distributed messaging for
developing full-featured virtual power systems with simula-
EMS Control Systems
State Estimation
Contingency AGC Wide-Area Damping
Screening Control
Economic Dispatch Historian and ClienDtsistributeCdlients Extended AGC System Separation
... Visualization Messaging Control Control
Modules:
Server ...
Simulators, Test Systems, and Scenarios Clients Clients Substation Simulators
Base Test Systems Power System PMU Measurement RTU Measurement
Simulator Simulator Simulator
High Renewable
Scenarios Control Signal Data Concentrator
Receiver ...
figure 1. The CURENT LTB architecture. AGC: automatic generation control; PMU: phasor measurement unit; RTU:
remote telemetry unit.
62 ieee power & energy magazine march/april 2020
for future hardware-in-the-loop capability. However, test functions (i.e., state estimation and visualization), sched-
systems and scenarios are typically stored in files and uling functions (i.e., economic dispatch), and security
may be specific to simulators. In the LTB, reduced-order functions (i.e., contingency screening). EMS functions
system models for the North American grid and various receive data from the downstream substation simulators
scenarios, i.e., future high-renewable cases and a mul- and output results to control systems, automation devices,
titerminal HVdc overlay network, have been developed or operators. The platform integrates standard routines
and are shown in Figure 2. available in open-source packages as well as advanced
EMS functions, such as the two-stage state estimator (see
Substation Simulators Rouhani et al. in the “For Further Reading” section). The
This module simulates the sensors and automation time resolutions for EMS functions range from seconds
devices that reside in substations. This category acts as to hours.
the intermediate component between the simulated physi-
cal system and data-driven applications and is composed Control System
of networked physical devices, including phasor measure- This category is a collection of advanced yet experimental
ment units (PMUs), remote telemetry units (RTUs), and control algorithms that researchers want to test and verify,
control automation devices. The PMU and RTU modules based on models and/or measurement data. Different from
receive raw simulation data from the simulator and out- the conventional local feedback controls modeled in the sim-
put simulated measurement data with noise, errors, and ulator, the control system aims at leveraging time-stamped
losses, which may be sampled from probability distribu- high-resolution measurement and estimation data for wide-
tions. In the other direction, automation devices receive area control. Control modules receive data directly from
control set points from the energy management system data concentrators or EMS functions and output control sig-
(EMS) and control system and modify the model param- nals to automated devices, which eventually act on the grid.
eters in the simulator. The time resolutions for control modules vary from seconds
to minutes.
Energy Management System
This type of module integrates the control-room functions Distributed Messaging Server and Clients
for optimizing the grid energy dispatch. More broadly, This includes a set of routines and application program inter-
it may also include system control and data acquisition faces (APIs) for distributed messaging between modules.
(SCADA) system functions for monitoring and control. Between any two communicating modules, the one providing
Modules in the EMS/SCADA system include monitoring input data to the other is called the upstream module, while
AC Transmission VSC-Based HVdc
Line Stations
Wind Farm
AC Load Bus
Synchronous
Generator
HVdc Line
figure 2. A future scenario of part of the reduced-order North American system with the continental HVdc overlay. Note
that not all ac transmission lines are visualized at the zoom level. VCS: voltage source converter.
march/april 2020 ieee power & energy magazine 63
The LTB strives to represent the data exchange structure
in real systems for operation and control by designing
the data flow between the decoupled modules.
the other one is referred to as the downstream module. There flow between the decoupled modules. The implemented data
is one data server along with multiple clients in the distributed flow shown in Figure 4 has the following main paths:
messaging environment, an example of which can be found in
Figure 3(a). The data server runs as a process, which binds to a ✔✔ The flow begins from static data files defining the test
socket using the transmission control protocol or interprocess systems and scenarios.
communication, and manages the client connections and data
delivery. Data clients are imported as APIs by modules for ✔✔ The simulator exchanges data with the substation sim-
connecting to the server, pulling in and sending out real-time ulators, namely, sensors and automation devices.
data as explained in Figure 3(b). Note that the server and cli-
ents provide only channels for communications, while it is left ✔✔ Measurement data (with realistic errors and delays)
to the modules to specify the data formats for data exchange. flows from sensors to the EMS and control system.
Data Flow and Program Workflow ✔✔ Some data, such as the estimated state, also flow from
the EMS to the control system.
The LTB strives to represent the data exchange structure in
real systems for operation and control by designing the data ✔✔ Both set-point signals and control signals flow back to
automation devices to close the loop.
The LTB relies on the APIs of the distributed messag-
ing server and client for implementing the data flow. The
APIs provided by the client allow the module to manage
Transparent to the User Distributed API for
Messaging Module B
Module B
Client
Module A
Module C API for Distributed Distributed
Module A Messaging Messaging Server
(a)
Client
Distributed API for
Messaging Module C
Client
(b)
figure 3. A distributed messaging environment: (a) an example of logical data streaming between three modules and
(b) the actual implementation of the three-module data streaming using the distributed messaging server and client APIs.
Model Parameters Visualization
Updated
Simulation Measurement EMS Data Files
Data Data Set Point
Signals Historian and
Sensors Archiving
Control System
Power System Automation march/april 2020
Simulator Devices
Data Files for Actuation
Systems and Signals
Scenarios
Model Parameters Control
Signals
figure 4. An illustration of the data flow for systemic closed-loop testing.
64 ieee power & energy magazine
The server and clients provide only channels
for communications, while it is left to the modules
to specify the data formats for data exchange.
connections and exchange data generically, or more specifi- A Demonstration Case Study
cally, for
This section showcases studies for wide-area, closed-loop
✔✔ connecting to a data server at a specified address control on the LTB. Data streaming from the modules is
✔✔ querying the names of modules connected to the same visualized in a web-based tool called LTB-Web, which ren-
ders plots and animations in the user’s browser. LTB-Web
server provides a systemic overview of the base electrical quanti-
✔✔ broadcasting or sending data to specified clients ties, including voltage magnitude, voltage phasors, and
✔✔ querying data availability and synchronizing data. frequency, on top of a geographic view. It also provides
In particular, the exchanged data in the LTB have the reload and replay function for comparing recorded test
been divided into parameter and time-stamped data, on cases and observing the control differences simultaneously.
which different streaming approaches have been applied.
Parameter data include the device parameters in the The controller developed and tested is a wide-area damp-
loaded test system as well as the parameters for algo- ing controller (WADC) for damping interarea oscillations.
rithms in modules. Time-stamped data are the values for The controller utilizes the measurements for computing addi-
the variables a module produces for a certain simulation tional reactive power control signals for actuators, which are
time. Typically, parameter data are requested a limited wind generators in this case study. In the event of actuator
number of times, whereas the time-stamped data are pro- failure or unavailability, the control allocator can dynami-
duced continuously. Therefore, the downstream module cally reallocate the control signal to the remaining control-
(the data consumer) is allowed to initiate the query of lers. The block diagram for the feedback loop with measure-
parameter data on demand, and the upstream module (the ment-based control allocation is depicted in Figure 5.
data producer) is allowed to initiate time-stamped data
streaming when available. Effectiveness of the Wide-Area
The LTB provides a handshake mechanism for request- Damping Controller
ing time-stamped variables. Before the simulation starts, The WADC has been integrated and tested as a MATLAB
downstream modules are required to identify themselves to module in the Western Electricity Coordinating Council
the upstream modules, which will then respond with the list (WECC) test system, using ePHASORsim and the custom
of variables it can provide during the runtime. The down- OpalAPIControl Python interface. The test system is a mod-
stream modules will respond with the indices of the vari- ified WECC 181-bus system to include a high wind penetra-
ables they need to complete the handshake. During the simu- tion rate (20% by energy). The system consists of 31 con-
lation, the upstream modules will send the requested data to ventional generators with a total capacity of 48.49 GW and
its downstream modules in an array that has the requested
order accompanied by a time stamp. table 1. The execution workflow for module
The workflow summarized in Table 1 is applied to inte- integration in the LTB.
grate the decoupled modules for systematic simulation.
Compared with a typical power system simulator, the LTB 1: Start the data server process.
requires additional steps to initiate the data server and the
modules in sequence. The initialization step consists of 2: Start the module processes.
three substeps:
1) self-initialization of modules for internal states 3: Initialization
2) querying parameters provided by the upstream module a) Begin the module self-initialization.
3) handshaking with the upstream module for variables. b) Query parameters from the upstream modules.
When the initialization is completed, the simula- c) Perform handshake with the upstream modules.
tor runs the computation, outputs data, and progresses 4: Start the simulation.
the simulation time. Modules will also enter the stage of a) The simulator calculates numerical integration.
active calculation and data exchange once the data arrives. b) The simulator and modules exchange data for each step.
The program execution will automatically exit if the pre- c) The simulator progresses the simulation time at wall-
defined simulation time is reached or an exception occurs
in any module. clock speed.
5: Exit when
a) the end of simulation is reached or an exception occurs.
march/april 2020 ieee power & energy magazine 65
The LTB provides an integrated platform as a
virtual power grid to validate and verify closed-loop
control technologies.
40 aggregated wind farms totaling 13.5 GW. The param- ratio D = 0.899% and the other one with f = 0.8121 Hz and
eters of the studied system were calibrated using the FNET/ D = 4.443%.
GridEye data with the main oscillation modes preserved.
A three-phase fault on a generator bus in the Los Angeles The frequency deviations from the nominal value are visu-
area with a duration of 10 cycles will trigger two oscillation alized on the geographic map to observe the control effects.
modes, one with a frequency f = 0.6540 Hz and a damping Using the LTB-Web visualization tool, the frequency oscil-
lation can be animated continuously. Screenshots from the
WADC Supervisory Modal-Based
Control Allocation
Power System PMUs Controller Actuators
0.11 Hz
figure 5. A block diagram of the WADC for closed-loop verification.
–0.11 Hz
10.73 s 11.45 s 12.24 s 13.01 s 13.88 s
(a) –0.11 Hz 0.11 Hz
10.73 s 11.45 s 12.24 s 13.01 s 13.88 s
(b)
figure 6. A visual comparison of the frequency deviations for the system (a) without WADC and (b) with full WADC allocation.
66 ieee power & energy magazine march/april 2020
The future plan also includes integration
with a hardware testbed to achieve the
hardware-in-the-loop capability.
system without WADC and with the full allocation of WADC at It is worth noting that all visualization and plots are cre-
different snapshots are illustrated in Figure 6, with the screen- ated using the LTB-Web visualization tool. LTB-Web pro-
shots taken in a full oscillation cycle starting at 10.73 s. (See vides a visual tool for researchers to verify effectiveness,
“LTB Demo: Dynamic Damping Control Allocation Using identify challenges, and even motivate them to explore new
Wind Generation” in the “For Further Reading” section.) The solutions to the observed power system problems.
visualization is colored based on the top scale, coloring the
frequency in a range between red and blue with the nominal Summary and Future Work
frequency being transparent. A severe frequency variation can
be observed in the case without the WADC, compared with the The LTB provides an integrated platform as a virtual
steady frequency with full control allocation. power grid to validate and verify closed-loop control
technologies. The decoupled software architecture in
Effectiveness of Dynamic Control Allocation which the decoupled modules are tied together by dis-
In the event of actuator unavailability or failure, the super- tributed messaging achieved a balance between system
visory modal-based control allocation algorithm will real- modeling complexity and test fidelity. The LTB also
locate the damping control signal to the available actuators. serves as a driver of research since it allows fast pro-
The same WECC system is simulated with 50% of all wind totyping of new models and grid infrastructures, direct
generators available. Figures 7 and 8 compare the bus fre- access to simulation and measurement data, and instant
quency deviation and tie-line flow for two scenarios: feedback of the wide-area control signals. In addi-
tion, a virtual control room has been established in the
1) a no wide-area damping control scenario CURENT research center as the facility to demonstrate
2) a wide-area damping control scenario with 50% of the LTB, as shown in Figure 9. Thus, the LTB serves
as a critical component to the success of various real-
wind actuators. time control research studies for the power grid and is
The improved damping can be observed for the scenario promising to advance the research community in elec-
with WADC [Figures 7(b) and 8(b)] as opposed to the sce- tric power systems, including the implementation and
nario with no wide-area damping control [Figures 7(a) 8(a)].
0.25 East Region 1,500 Active Power
0.20 South Region 1,400
0.15 1,300 5 10 15 20 25 30 35 40 45
0.10 5 10 15 20 25 30 35 40 45 1,200 (a)
0.05 (a) 1,100
1,000
0
–0.05 900
–0.10
–0.15
0.25 East Region 1,500 Active Power
0.20 South Region 1,400
0.15 1,300 5 10 15 20 25 30 35 40 45
0.10 5 10 15 20 25 30 35 40 45 1,200 (b)
0.05 (b) 1,100
1,000
0
–0.05 900
–0.10 800
figure 7. The frequency deviation (hertz, from 60 Hz) on figure 8. The active power tie-line flow between the east
buses in the east and south regions: the scenario (a) without and the south regions of WECC: the scenario (a) without
wide-area damping control and (b) with wide-area damp- wide-area damping control and (b) with wide-area damp-
ing control using wind farms as actuators. ing control using wind farms as actuators.
march/april 2020 ieee power & energy magazine 67
figure 9. The virtual control room at CURENT serving as the demonstration facility of the LTB.
d emonstration of monitoring, modeling, control, and Simulation of Cyber-Physical Energy Systems (MSCPES),
actuation functions. pp. 1–6. doi: 10.1109/MSCPES.2017.8064542.
The LTB architecture allows the integration of commu- L. Vanfretti, T. Rabuzin, M. Baudette, and M. Murad,
nication system emulators, which will enable the simulation “iTesla Power Systems Library (iPSL): A Modelica library
of cyberattacks on electrical power systems, a research area for phasor time-domain simulations,” SoftwareX, vol. 5, pp.
of growing importance. With the recent implementation of 84–88, May 2016. doi: 10.1016/j.softx.2016.05.001.
power management unit data streaming using IEEE Stan-
dard for Synchrophasor Measurements for Power Systems, H. Cui and F. Li, “ANDES : A Python-based cyber-
IEEE Standard C37.118, protocol and substation control physical power system simulation tool,” in Proc. North
using IEC 61850, future work will focus on the cyberphysi- American Power Symp., 2018, pp. 1–5. doi: 10.1109/
cal events that stem from cyberattacks including heavy NAPS.2018.8600596.
traffic, sniffing, and data breach, which eventually cause
stability issues in the physical grid. The future plan also A. Rouhani and A. Abur, “Linear phasor estima-
includes integration with a hardware testbed to achieve the tor assisted dynamic state estimation,” IEEE Trans.
hardware-in-the-loop capability. Smart Grid, vol. 9, no. 1, pp. 211–219, 2018. doi: 10.1109/
TSG.2016.2548244.
Acknowledgments
M. E. Raoufat, K. Tomsovic, and S. M. Djouadi, “Dy-
This work is supported by the Engineering Research Center namic control allocation for damping of inter-area oscilla-
program of the NSF and the DoE under NSF Award Num- tions,” IEEE Trans. Power Syst., vol. 32, no. 6, pp. 4894–
ber EEC-1041877 and the CURENT Industry Partnership 4903, 2017. doi: 10.1109/TPWRS.2017.2686808.
Program. Any opinions, findings and conclusions or rec-
ommendations expressed in the material are those of the “LTB demo: Damping control allocation using wind
author(s) and do not necessarily reflect those of the NSF and generation.” Accessed on: Jan. 1, 2020. [Online]. Available:
the DoE. We would like to acknowledge contributions from https://youtu.be/OtCFRHMtdo8
the CURENT LTB project team, including faculty, staff,
and research assistants at the University of Tennessee, Rens- F. Li, K. Tomosvic, and H. Cui, “An integrated testbed for
selaer Polytechnic Institute, Northeastern University, and power system monitoring, modeling, control and actuation,”
Tuskegee University. in Proc. 11th IET Int. Conf. Advances in Power System Con-
trol, Operation and Management (APSCOM), Hong Kong,
For Further Reading China, Nov. 11–15, 2018. doi: 10.1049/cp.2018.1735.
B. Palmintier, D. Krishnamurthy, P. Top, S. Smith, J. Daily, Biographies
and J. Fuller, “Design of the HELICS high-performance
transmission-distribution-communication-market co-simu- Fangxing Li is with the University of Tennessee, Knoxville.
lation framework,” in Proc. 2017 Workshop on Modeling and
Kevin Tomsovic is with the University of Tennessee,
Knoxville.
Hantao Cui is with the the University of Tennessee,
Knoxville. p&e
68 ieee power & energy magazine march/april 2020
Energy Storage
Control Capability
Expansion
©ISTOCKPHOTO.COM/PETOVARGA
Achieving Better Technoeconomic Benefits at
Portland General Electric’s Salem Smart Power Center
By Jan Alam, TTHE VALUE PROPOSITION FOR ENERGY STORAGE SYSTEMS
Patrick Balducci, (ESSs) is a key topic for creating and advancing its acceptance within the elec-
Kevin Whitener, tric power sector, particularly for electric utilities. Although ESS as a technol-
and Steve Cox ogy is gaining popularity within the electric utility industry, its anticipated
value streams are not fully understood, quantified, and demonstrated. The
Digital Object Identifier 10.1109/MPE.2019.2959115 unavailability of suitable demonstration sites/projects, the lack of a deep under-
Date of current version: 19 February 2020 standing of available economic opportunities, and the deployment complexi-
ties associated with pursuing those opportunities are some of the reasons that
complicate its value demonstration. The lessons learned from holistic demon-
stration projects covering key steps, e.g., economic value stream identification,
evaluation, and its subsequent realization via suitable control strategies, could
help electric utilities learn to manage ESS adoption challenges better.
Co-optimizing multiple services, or “value stacking” for the maxi-
mization of economic return, is a highly discussed concept in the ESS
march/april 2020 1540-7977/20©2020IEEE ieee power & energy magazine 69
industry. Although significant theoretical research has been launched in 2010 as a five-year program partially funded by
conducted on this concept using look-ahead optimization the U.S. Department of Energy (DoE) through the Ameri-
with an assumption of perfect foresight on the variables of can Recovery and Reinvestment Act. Program participants
interest (e.g., electricity price, load, and renewable power included Bonneville Power Administration, 11 utilities from
generation), utilities do not yet have enough confidence in five states from the Pacific Northwest region (Washington,
its practicality. Uncertainties pertaining to market-driven Oregon, Idaho, Montana, and Wyoming), and six technology
parameters add to the complexity of optimal ESS opera- partners. PGE, an investor-owned utility, was a participant
tion, which adheres to the constraints associated with the in the PNWSGDP program that cosponsored the SSPC proj-
technoeconomic requirements of multiple stakeholders of ect—an 8,000-square foot test and demonstration facility at
a given portfolio of ESS assets. Making strategic decisions the utility’s Oxford substation in Salem. This facility’s staff
over control approaches (e.g., rule based versus optimal) developed a smart grid platform to integrate residential and
and implementation options (e.g., building from scratch commercial demand response assets; grid-connected, com-
versus customizing off-the-shelf products) that consider the mercial-dispatchable standby generation; grid-connected
tradeoffs associated with usefulness, simplicity, and future battery storage; distributed switching; and a commercial
expansion is, therefore, not a trivial task. Utilities consider- microgrid. DoE funding in 2010 covered 50% of the cost
ing the inclusion of ESSs into their asset portfolio could ben- of this US$25 million effort, and the remaining 50% was
efit significantly from lessons gleaned from demonstration equally shared by the utility (US$6.5 million) and its princi-
projects that dealt with such issues. pal technology partners Enerdel, Eaton, and Alstom.
This article reports on a transformative project aimed System Description
at enhancing the control capabilities of a Portland General The lithium-ion ESS is composed of 20 modular energy stor-
Electric (PGE)-owned 5-MW/1.25-MWh ESS located at the age racks organized into five blocks, with each containing
Salem Smart Power Center (SSPC) in Oregon toward achiev- four racks. Each rack consists of 18 small drawer-type units
ing better technoeconomic benefits. The steps used for devel- with four battery modules, for a total of 1,440 modules in the
oping a value-driven control capability are illustrated, starting system. Each battery module contains 12 series-connected
from the evaluation of economic opportunities that drove the lithium-ion cells, for a total of 48 series-connected cells in a
coordination of multiple services to be delivered by an ESS to drawer unit. The organization of the cells, modules, and racks
implementation and testing. The lessons learned during criti- in a battery block is shown in Figure 1. A battery string is
cal processes are identified for the benefit of the ESS industry. composed of three drawers in series and operates at approxi-
mately 600 Vdc. The lithium-ion cells in the battery modules
SSPC Energy Storage System are rated at 3,000 charge-discharge cycles. A programmable
logic controller (PLC)-based battery management system
Background (BMS) performs battery monitoring functions only; control
SSPC was originally a part of the Pacific Northwest Smart is accomplished by a separate PLC-based control system.
Grid Demonstration Project (PNWSGDP), which was
Vault Rack Cells in a
Module
Drawer
Unit Four Modules in
a Drawer Unit
Blocks
figure 1. The organization of cells, modules, vaults, and racks in an ESS block. march/april 2020
70 ieee power & energy magazine
The inverters provide full four-quadrant operation with the capability
to import and export real and reactive power, which offers the
opportunity to deploy the ESS for various ancillary services.
Each rack of battery modules feeds a bank of 2 × 125-kVA Control Capability Expansion of SSPC
inverters, shown in Figure 2(a), which makes the output of a
single block consisting of four racks equivalent to 1 MVA. The control of ESSs for an electric utility could take two
Hence, five blocks of battery modules feeding a total of 20 different perspectives, as illustrated in Figure 3. One is for
banks of 2 × 125-kVA inverters result in a system output of the maximization of the ESS’s economic benefit as a local
5 MVA. The inverters provide full four-quadrant operation asset connected to a local feeder or within a small part of the
with the capability to import and export real and reactive utility’s network, and the other is to utilize the ESS as a part
power, which offers the opportunity to deploy the ESS for
various ancillary services.
Deployed Control System at the SSPC Site
The ESS is controlled by a PLC-based control system, which
is depicted in Figure 2(b). The control system creates an
interface among the inverters, power meters, the BMS, and
the upstream system controls that operate the ESS in a vari-
ety of modes according to the utility’s specification and intel-
ligently coordinates the operation of the inverters to balance
demand among the battery blocks.
Evolution of Use Cases
As a part of the PNWSGDP, the SSPC ESS was required
to demonstrate the capabilities needed to perform a set
of use cases relevant to the program goals. Although the
overall PNWSGDP was completed by the end of January (a) (b)
2015, it was decided to continue using the SSPC facility
consistent with the program’s original purpose and simul- figure 2. An ESS control system: the (a) two-times power
taneously optimize its value to its customers as a grid- expert inverter banks and (b) PLC-based control system.
integrated asset. A pool of 15
use cases involving the ESS and
other SSPC assets was created by Asset Economic Operational System-Level
the utility covering transactive Evaluation Data and Models Economic Dispatch
energy, energy shifting, demand
response, ancillary services, dis-
tribution automation, and emer-
gency/backup/reliability services. System Operation Platform
Over the course of time, some of the Minimize System Operation Cost
use cases were discontinued due
to technical reasons or diminish-
ing importance. Site Controller/Local Resource Optimizer
For the control system expan- Maximize Asset Economic Benefit
sion project, use cases were revis-
ited and evaluated in the context
of current economic opportuni-
ties. This economic evaluation SSPC ESS
was the basis for the control sys-
tem expansion process described
in the following section. figure 3. ESS control and coordination framework perspectives.
march/april 2020 ieee power & energy magazine 71
The knowledge gained on use-case specifics and relative
economic benefits could provide useful information for
binding multiple services together.
of the utility’s asset pool for minimizing the global, day-to- platform and automatic or operator-fed dispatch schedules
day system operation cost. For the first case, the identifica- for local asset benefit maximization. The rest of this section
tion and evaluation of a set of economic opportunities, or is focused on control expansion for benefit maximization of
use cases, in relation to the local portion of the network are the ESS as a local asset. A summary of the SSPC ESS eco-
performed, and the use cases could be implemented through nomic evaluation findings is presented in the following section,
a site controller. For the second case, the ESS will need followed by the approach used for control strategy develop-
to be integrated within a central optimization framework ment and implementation.
(e.g., an economic dispatch model) of the utility, and ESS
control commands would be derived from dispatch instruc- Economic Evaluation of Use Cases—The Basis
tions issued by the utility’s system operation platform. This of Control System Expansion
platform is essentially a suite of software tools used for dis- Following discussions with PGE personnel and assess-
patching resources economically while satisfying system ments performed by Pacific Northwest National Labora-
energy, capacity, and ancillary service needs and resource tory (PNNL), nine use cases were considered for economic
cost and capability constraints. The module that performs evaluation. PNNL’s battery storage evaluation tool was used
the dispatch task is often referred to as an energy manage- to perform an hourly look-ahead optimization to determine
ment system (EMS). The following are some key reasons the ESS power schedules with tradeoffs among different
why the direct implementation of the second approach could services while taking into account battery performance
be difficult for a utility without prior experience on ESS parameters (e.g., round-trip efficiency) and operational lim-
integration and operation: its (e.g., power/state of charge limits and annual usage obli-
gations) and technical and financial (e.g., energy/capacity/
✔✔ The ESS must be modeled using its performance ancillary service price) aspects of each use case. The tool
characteristics, and integrating constraints into the was then used to simulate battery operation and estimate
EMS platform and dispatch signals will be created the co-optimized value of the modeled services. The eco-
based on system-level economic dispatch require- nomic evaluation also provides information on various use
ments, as shown in Figure 3. However, this process cases that would be beneficial for implementation of the
requires significant time and effort due to modeling use-case control strategies, i.e., ranking the benefits from
complexities, system integration, testing, and valida- use cases, ranges of state-of-charge (SoC) variation while
tion requirements. performing the use cases, typical conditions that cause tran-
sition between use cases or causes an interruption (e.g., the
✔✔ The modeling of the ESS for integration with the sys- SoC out of limit). (The detailed modeling and formulation
tem operation platform requires information that may of this method can be found in Balducci et al. in the “For
be difficult to obtain without analyzing operational Further Reading” section.) Figure 4 presents a schematic
data; local economic operation could provide such of the economic evaluation process including the estimated
information. net present value benefit of the use cases considered over
a lifecycle of 20 years, with an ESS replacement after
Because of these reasons, it is not uncommon for utili- 10 years of operation.
ties to start the operation of an ESS using a local controller
without its full integration with a system operation platform. Development of Control Strategies
A similar approach was used for the SSPC ESS. When first One key aspect that differentiates between the economic
developed, the utility tested the ESS capabilities to perform evaluation for determining maximum benefit and the
various use cases in an individual fashion. However, those implementation of control strategies to maximize the ben-
use cases were not in regular operation. During the initial efit is that the evaluation works on historical or projected
phase of the control capability expansion project, control data and estimates the benefits over a given time horizon
strategies were built to perform multiple use cases through assuming perfect foresight while during actual operation, a
a rule-based coordination strategy. Currently, the utility is control system needs to make a decision in real time based
working to integrate the SSPC ESS with its system opera- on the prevailing situation. Therefore, a co-optimization
tion platform. A detailed discussion on this aspect is pre- process used for economic evaluation cannot be directly
sented in the “Integration of ESS with System Operation
Platform” section. A site controller could be designed to
switch between operations guided by a system operation
72 ieee power & energy magazine march/april 2020
Integration with a system operation platform involves
the modeling of the ESS using the resource
modeling tool used by the utility.
replicated for actual implementation. However, the knowl- coordinate the ESS operation among multiple use cases and
edge gained on use-case specifics and relative economic 2) charge/discharge the ESS in a manner that satisfies the
benefits could provide useful information for binding mul- requirements of each use case such that operational con-
tiple services together. straints are not violated. Although it would be ideal to use a
controller that could perform the real-time co-optimization
The value-driven control of an ESS essentially refers to of multiple use cases, it is not always practical for utilities to
operating the ESS under one or more bundled use cases with implement such an option due to reasons, e.g., the desire for
a view toward enhancing economic benefits. Therefore, a a simple and robust approach or a lack of adequate informa-
control strategy supporting a value-driven control approach tion to perform real-time optimization. Therefore, a set of
of an ESS will need to perform two basic functions: 1)
Use Cases US$7,000,000
Volt-Var/CVR (VVO/CVR)
Nonspinning Reserve (NSR) US$6,000,000 VVO/CVR,
Spinning Reserve (SPR) SPR, and NSR
Primary Frequency Response (PFR)
Regulation Down (RDN) US$5,000,000
Regulation Up (RUP) US$4,000,000 PFR
Demand Response (DR) US$3,000,000
Arbitrage (ARB) US$2,000,000 RDN
US$1,000,000 RUP
Battery Storage
Evaluation Tool US$0 DR
Use-Case Specifics ARB
ESS Parameters
Charging Cost
Financial Information
US$(1,000,000)
Economic
Evaluation Output
Economic Benefit and Rank
Use-Case Priority
Optimum Dispatch Profile
SoC Variations
Use-Case Transition Conditions
figure 4. The economic evaluation process of SSPC ESSs. CVR: conservation voltage reduction.
march/april 2020 ieee power & energy magazine 73
A set of rules developed from an off-line economic
evaluation by co-optimizing multiple use cases
could be used as a reasonable starting point.
rules developed from an off-line economic evaluation by co- cause use cases to switch from one to another. This informa-
optimizing multiple use cases could be used as a reasonable tion provided valuable insight while designing a rule-based
starting point. charge/discharge strategy.
This project used a similar approach where the initial set Figure 5 is a conceptual diagram of the multiple use-case
of rules was developed using the findings of economic evalu- coordination strategy implemented at SSPC. By default,
ation. For instance, assigning priority to each use case is one the controller operates within a main coordination loop
of the many options used for the coordination of multiple use that maintains the SoC for the highest priority use case,
cases; the relative economic benefit of SSPC use cases was enables scheduled services, and makes transitions to a use-
used as a basis for the prioritization of multiple use cases for case control function with fulfillment of the conditions of
value-based control. An optimal dispatch profile of the SSPC entry. Although operating within a use-case control loop,
ESS obtained from the economic evaluation provided useful the controller performs scheduled charge/discharge opera-
information on 1) the typical time and length of operation tions while monitoring for conditions to exit the loop (e.g.,
of various use cases for maximizing benefits, 2) the change the schedule finished, the SoC limit violated, or a change of
in SoC during those time periods, and 3) the conditions that priority ranking).
• Maintain SoC for Top Implementation
PGE has deployed a PLC-based
Priority Service control system at SSPC, and con-
trol capability was expanded by
• Enable Scheduled Services adding new routines to the exist-
ing PLC programs. Strategies
• Check for Active Services developed for the coordination of
multiple use cases and the control
Main of individual use cases were first
represented using flowcharts for
Entry Coordination discussion, understanding, and
UC1 refinement and were subsequently
Loop [C ENT] • Check for Priority Ranking coded into the PLC.
[C EXT]
Exit • Monitor SoC and Make Three status variables are used
for each use case: enabled, ready,
Transition to Main Loop and active. A priority setting option
is developed for setting the priority
UCn • Perform Scheduled of each use case. For manual entry
Charge/Discharge mode, day-ahead schedules are
entered using hourly values for the
UC2 next 24 h.
figure 5. A rule-based coordination of multiple use cases. UC: use case; CENT: condi- Data points used to facilitate
tions of entry; CEXT: conditions of exit. communication between the util-
ity’s EMS and SSPC’s ESS are
EEMSS SSPC Site presented in Figure 6. For the
overall site, the availability, SoC,
• Regulation MW Set Point • Availability MW and MVar outputs, and volt-
• Contingency Reserve • SoC age are communicated to the
• MW EMS. The status and sched-
MW Set Point • Mvar uling variables are communi-
• Arbitrage MW Set Point • kV cated for each service. For
regulation, energy arbitrage, and
Use Case
• Enabled, Ready, and Active
• Current Day Start, End, and Priority
• Next Day Start, End, and Priority
figure 6. The shared data point between EMS and SSPC ESSs.
74 ieee power & energy magazine march/april 2020
contingency reserve, the EMS will send the MW set point ing the necessary feasibility tests and optimizing across the
to the ESS. larger EIM footprint, sends signals to PGE that are then used
Integration of the ESS With by the BAO to dispatch the resources through the utility’s
System Operation Platform EMS. The overall system operation process is outlined
in Figure 7.
To achieve the full benefit of the SSPC ESS in support of the
utility’s day-to-day system operation needs, the ESS must be Pathway to Integration With
incorporated as a resource in its system operation platform System Operation Platform
so that the EMS could dispatch the ESS as needed. However, To integrate the SSPC ESS with PGE’s day-to-day opera-
fully integrating the ESS is not a trivial task. It requires an tion platform, the ESS must be modeled using the utility’s
understanding of the system operation scheme and the cus- resource modeling tool. The major parameters used to model
tomization of software platforms to incorporate the ESS. The the ESS with this tool are listed in Table 1 as are the sources
following sections provide several system operation aspects of information used for determining parameter values.
and discuss a potential option for including the ESS within Once the ESS is modeled using the resource modeling
the company’s operational platform. tool, it will be available for daily allocation into various ser-
vices. The allocation schedule produced will eventually be
Day-to-Day System Operation used for the day-ahead scheduling of ESS operations.
Power operations (PowerOps) and balancing authority opera- The utility is also building an EMS interface for dispatching
tors (BAOs) are the main groups involved in the day-to-day its ESS assets (SSPC and future units). An illustrative version
operation of the utility’s system.
There are two functions of Pow-
erOps: day-ahead and real-time
scheduling. The day-ahead sched- PowerOps Resource Modeling Day-Ahead Schedule
uling function uses an optimiza- Day-Ahead Scheduling
tion tool to model generating • Heat Rate • Load Forecast
resources using parameters, e.g., Real-Time Scheduling• Ramp Rate • Resource Availability
heat rate, ramp rate, min/max • Min/Max Generation • Gas Purchase
generation, and the allocation of
resources to a variety of services, Resource Allocation Contract
e.g., baseload, frequency response, • Long-/Short-Term
and reserves. This function then • Base Load
creates hourly day-ahead sched- • Frequency Response Hydro Contract
• Reserve • Wind Forecast
ules via software, using data on
load forecasts, the availability of
resources, gas purchase contracts,
short-/long-term hydro contracts,
and wind forecasts. The day-ahead Execution of Day-Ahead Schedule
schedule is then transferred to the
real-time function for execution. • Several Hours to Under an
Depending on any changes in Hour Ahead
the forecast and system condi-
tion, the real-time group modifies • Accommodate Change in System
the day-ahead schedule within a Condition and Forecast
• Communicates With CAISO for
EIM Participation
period of under an hour to several
hours ahead. The real-time func-
tion also sends hourly plans and
schedules to the BAO and Califor-
nia Independent System Operator
(CAISO) for participating in the EMS
energy imbalance market (EIM). BAOs • Dispatch Resources
Plans for each hour are sent about
60 min before the hour, while • Manage Real-Time
revisions are sent (by the BAO) Changes
40 min before the hour. The CAISO
EIM market engine, upon perform- figure 7. The day-to-day system operation scheme. min/max: minimum/maximum.
march/april 2020 ieee power & energy magazine 75
of the EMS screen is shown in Figure 8, which will evolve its thermal and hydro fleets (e.g., the actual and desired genera-
as the system integration process continues. For a given ESS tion, the options for manual power set point, and the selection
unit, for instance, SSPC, the top portion of the screen shows an of control and regulation modes). An availability parameter is
assortment of parameters and modes similar to the displays for added to indicate whether or not a given ESS unit is available
for operation. The middle portion
table 1. The parameters for ESS modeling using the of the screen contains graphical
system operation platform. representations of the power output
Parameter Source of Information and the ESS’s SoC. Priority setting
Min/max capacity Nameplate rating, testing report, and operational options for each use case and their
experience corresponding status flags (enable,
Charging/discharging rate Testing report and operational experience ready, and active) are shown at the
bottom of the screen.
Efficiency Testing report and operational experience SSPC ESS in Operation
Self-discharge rate Manufacturer’s document and operational experience
Fixed O&M cost Operating plan and financial report This section presents several use-
Variable O&M cost Financial report case operation snapshots from the
Start-up and shut-down cost Financial report and operational experience SSPC site and describes some prac-
tical features of the control system.
Min/max down time Operational experience Use-Case
Operation Snapshots
Daily min/max starts/energy Operating plan and manufacturer’s document Although the SSPC ESS is still
O&M: operations and maintenance. in the process of being integrated
figure 8. An illustrative version of an EMS screen for an ESS operation. march/april 2020
76 ieee power & energy magazine
with the utility system operation platform, operational A few snapshots of ESS operation under individual
data from the site could provide useful information in use cases are displayed in Figure 9. Primary frequency
analyzing the performance of the ESS under various use response (PFR), which replicates a generator’s governor
cases. Potential applications of the ESS while operat- response by responding to a reduction in system fre-
ing under the jurisdiction of the utility system opera- quency, is the utility’s highest-value use case. The power
tion platform would be similar (with a few exceptions profile produced by SSPC during a PFR operation is pre-
related to local operation) to the use cases considered for sented in Figure 9(a); it is essentially a step discharge of
the local asset benefit maximization goal. Therefore, the the battery at 4.7 MW for roughly 3 min before ramping
data and lessons learned from the local asset operation down the discharge power to zero. A post-PFR charg-
perspective could be used to assess how the ESS would ing is accomplished by the main coordination loop (see
perform while engaged by the EMS and would provide Figure 5) to maintain a desired SoC. Regulation service
useful information for the modeling of and integration requires an ESS to follow a set of charge/discharge com-
with this platform. mands at intervals of a few seconds (e.g., 4 s in CAISO).
Power (kW) SoC (%) Power (kW) SoC (%)
6,000 Discharge to Provide PFR 100 6,000 100
5,000 80 4,000
4,000 2,000 80
Power (kW) 3,000 60 SoC (%) 60 SoC (%)
2,000 Post-PFR Charging 40 Power (kW) 0 40
1,000 –2,000 20
20 0
0 –4,000 8:36 a.m.
–1,000 0 –6,000
6:24 p.m.
6:04 p.m. 8:08 a.m.
Time of Day Time of Day
(a) (b)
Power (kW) SoC (%) Measured Voltage (V)
Voltage Set Point (V)
400 100 Reactive Power (kVar)
200 155-kW Demand Response 80
12,850 2,000
12,800
Power (kW) 0 60 SoC (%) 12,750 1,000
–200 40 Voltage (V)
–400 12,700 0 (kVar)
12,650
–600 591-kW Charge to Maintain SoC 20 –1,000
12,600
–800 0 2:45 p.m. –2,000
3:55 p.m. 6:00 p.m. 3:15 p.m.
Time of Day Time of Day
(d)
(c)
6,000 PFR ESS Resumes Regulation
4,000 Function
Power (kW) 2,000 Triggered
0 ESS Providing Regulation Regulation PFR
–2,000
–4,000 Time of Day 1:56 p.m.
1:46 p.m. (e)
figure 9. The SSPC performing use-case operations individually and bundled.
march/april 2020 ieee power & energy magazine 77
This is tested by commanding the ESS to charge/discharge for which use cases the ESS was ready (green), active (red),
according to the variation of area control error signal in and acknowledged but not capable (yellow). An illustration
the utility balancing area [the ESS power and SoC profiles of this feature, the ESS’s operation on 27 March 2019, is
corresponding to this operation are shown in Figure 9(b)]. provided in Figure 10. Ready means the service has been
The demand response function is illustrated in Figure 9(c) scheduled, and the system can provide this service when it is
where the ESS is discharged at 155 kW from 3:55 p.m. called upon. For example, PFR is normally green, meaning
for approximately 2 h. Once the schedule is completed, that it can respond anytime an event occurs. Active means
the ESS goes into charging mode to maintain SoC at the the service is currently being dispatched. For example, PFR
required level. Performing demand response requires the has been triggered due to a low-frequency event and the
ability to discharge at a desired power for a desired period. system is now discharging. Acknowledged but not capable
indicates the inability of the ESS to provide a requested
Other use cases that need similar capability (e.g., contin- service. For instance, assume an operator has scheduled a
gency reserve) could benefit from the analysis of the ESS’s service, i.e., Reg Down. But because Reg Down requires
demand response. The volt-var function needs the ESS inverter the battery to charge and current SoC is at high limit, the
to generate or consume reactive power to either hold control system acknowledges the operator’s schedule but could not
voltage at a given set point or maintain a voltage limit. The react if called upon. Currently, PFR is kept enabled for the
volt-var function built into the SSPC control system during whole day. An analysis of historical daily operation profiles
the early-stage smart grid demonstration project was refined can provide useful insight on frequency, length, and the
and integrated with additional functions during the control interruption statistics of various use cases and can be used
capability expansion project. A var control demonstration for to enhance rule-based control strategies, build new condi-
controlling the 12-kV voltage at SSPC is depicted in Fig- tions for better coordination, and so on.
ure 9(d), where the actual voltage, voltage set points, and the
kvar required to control voltage are shown. The maximum Financial Value Tracker
deviation between the set point and measured voltage was Recognizing the importance of understanding the value gen-
found to be 0.65%. Figure 9(e) is an example of how setting eration performance of an ESS, a feature is combined with
up the priority ranking allows the ESS to coordinate multiple the SSPC ESS to track the value generated under various use
use cases. In this figure, both PFR and regulation are enabled cases. Although the actual revenue may differ because of
over the same time period, while the regulation function was numerous reasons (e.g., dynamic price change and financial
initially active. However, with the detection of a need to pro- settlement), this feature could at least provide some indica-
vide PFR, the ESS exits the regulation function and enters the tion of the benefit an ESS has generated at a given point in
PFR function, which is the highest priority. Once the opera- time. Currently, the SSPC control system is configured to
tion under PFR is finished, the regulation function is resumed estimate value considering two aspects: one is how long it
because it is still enabled and the ESS is ready to perform. has been available for a given service and the other is the
actual energy exchanged to perform the service. An illus-
A Day in the Life of the SSPC ESS tration of the idea is presented in an SSPC control system
A feature is included in the control system that will summa- screenshot shown in Figure 11.
rize the operation of the ESS over the last 24 h by indicating
figure 10. A day in the life of the SSPC ESS. march/april 2020
78 ieee power & energy magazine
A concept of value multipliers (e.g., US$ per hour for operation cost minimization perspective, implementation
availability and US$ per MWh for energy exchange) is of the latter is not a trivial exercise due to its complexity
proposed where these multipliers, determined using some and lack of adequate information. Launching an ESS oper-
form of averaging or levelizing technique, are used to esti- ation with a local asset value maximization perspective
mate the benefit generated from a service. If configured could provide important information and knowledge,
to match the pricing and payment structure within a given which would support the ESS control from a day-to-day
market jurisdiction, these estimated values could provide system operation perspective.
useful insight for improving ESS value generation. For
instance, if regulation revenue in a market region depends Large electric utilities owning generation, transmission,
on regulation capacity and regulation mileage, the value and distribution assets are typically organized into multiple
multipliers could be configured in that way and could also groups responsible for many business functions and could
be updated in real time so that the estimated value provides have diverse views on the best use of an asset. While expand-
a reasonable representation of the revenue generated from ing the control capabilities of the SSPC ESS, it was observed
regulation service, with caveats related to the assump- that, in practice, it is difficult to have multiple groups agree
tions used for determining the value multipliers. The value to finalize the use cases to be pursued and obtain the neces-
tracker screen also shows the ESS charging cost to prepare sary support for implementation. An effective communica-
for the services. tion strategy would be necessary for the socialization of the
use cases proposed. Economic evaluation from a local asset
Lessons for Electric Utilities benefit maximization perspective could be an effective way
to facilitate this discussion.
The SSPC ESS control capability expansion project pro-
vided useful lessons on enabling multiple use-case opera- Whereas the co-optimization of multiple use cases for
tions of ESSs. Electric utilities that intend to incorporate economic benefit evaluation is performed using optimiza-
energy storage within their asset portfolio could benefit tion engines, the field implementation of such engines for
from these lessons. Considering their overall importance to control deployment is not trivial and typically not preferred
the advancement of the energy storage industry, some of the by many utilities during the initial phase of the project due
lessons are summarized in this section. to its complexity and the time and effort required. The util-
ity chose to translate the lessons from the economic evalu-
Although the control of an ESS owned by an elec- ation into a set of rules to coordinate and control multiple
tric utility could be performed either from a local asset use cases. Information obtained from the economic evalua-
value maximization perspective or a day-to-day system tion (e.g., priority ranking, the SoC variation range, typical
figure 11. The value-tracking feature of the SSPC control system. ieee power & energy magazine 79
march/april 2020
The selection of an appropriate platform
for implementing control strategies depends on
multiple aspects and varies case by case.
operation time, and the conditions that cause transition against local system needs while establishing control proto-
among use cases or interruption) is very useful for generat- cols and market-bidding strategies.
ing such rules. As more data and knowledge are gathered
on a particular ESS project, the rules could be refined for Acknowledgment
more optimal performance or the deployment of optimiza-
tion engines could be considered. The research work conducted by Pacific Northwest National
Laboratory for this project is funded by the Energy Storage
The selection of an appropriate platform for implement- Program under the Office of Electricity, the U.S. Depart-
ing control strategies depends on multiple aspects and var- ment of Energy.
ies case by case. However, considering the tradeoffs associ-
ated with the technical features, computational capabilities, For Further Reading
simplicity of use, and options for future expansion would
provide useful guidance when selecting the appropriate plat- P. J. Balducci et al., “The Salem Smart Power Center: An assess-
form. For this project, the utility chose to build the control ment of battery performance and economic potential,” Pacific
system from scratch using a PLC-based controller for vari- Northwest Nat. Lab., Richland, WA, Rep. PNNL-26858, 2017.
ous strategic reasons, including developing in-house exper-
tise, reducing dependency on external resources, and easier D. Wu, C. Jin, P. J. Balducci, and M. C. Kintner-Meyer,
modification, expansion, and scalability. “An energy storage assessment: using optimal control strate-
gies to capture multiple services,” in Proc. IEEE Power &
The inclusion of certain features with the control sys- Energy Society General Meeting, Denver, CO, July 26–30,
tem could make it easier to understand ESS operation 2015, pp. 1–5. doi: 10.1109/PESGM.2015.7285820.
under multiple use cases and to generate information
for the expansion of control capabilities. SSPC includes California ISO, “Standards for imports of regulation.”
visual aids (an animated and colored flowchart) for fol- Accessed on: Nov. 11, 2019. [Online]. Available: https://
lowing the operation of the ESS under various use cases, www.caiso.com / Documents/ ISOStandards_Imports
a daily operation summary chart to gain better insight on -Regulation.pdf
daily operation, and an economic value tracking feature
to provide a real-time visual indication of the economic D. Manz, R. Piwko, and N. Miller, “Look before you leap:
values being generated. The role of energy storage in the grid,” IEEE Power Energy
Mag., vol. 10, no. 4, pp. 75–84, July/Aug. 2018. doi: 10.1109/
In many cases, an ESS would ultimately be integrated MPE.2012.2196337.
with the central day-to-day operation platform of a utility.
The ESS would then be a part of the utility’s portfolio of J. Araiza, Jr., J. Hambrick, J. Moon, M. Starke, and C.
assets and would be scheduled and dispatched to minimize Vartanian, “Grid energy-storage projects: Engineers build-
the global system operation cost. Integration with a system ing and using knowledge in emerging projects,” IEEE Elec-
operation platform involves the modeling of the ESS using trific. Mag., vol. 6, no. 3, pp. 14–19, Sept. 2018. doi: 10.1109/
the resource modeling tool used by the utility. Typically, MELE.2018.2849842.
these tools need information on operational costs and tech-
nical constraints, which is difficult to generate without prior E. Namor, F. Sossan, R. Cherkaoui, and M. Paolone,
operating data for a given ESS. The operation of the ESS “Control of battery storage systems for the simultaneous
under a local asset benefit maximization could provide use- provision of multiple services,” IEEE Trans. Smart Grid,
ful data in this regard. vol. 10, no. 3, pp. 2799–2808, May 2019. doi: 10.1109/
TSG.2018.2810781.
Participating in electricity markets, for instance, the
Western EIM for the case of PGE, introduces additional lay- Biographies
ers of complexity into the ESS control functions. In addi-
tion to the scheduling of the ESS along with other assets Jan Alam is with Pacific Northwest National Laboratory,
across its system to address local system needs, additional Richland, Washington.
coordination would be required through the design of daily
bids and the integration of market instructions into daily dis- Patrick Balducci is with Pacific Northwest National
patch. The benefits of EIM participation should be weighed Laboratory, Portland, Oregon.
Kevin Whitener is with Portland General Electric, Port-
land, Oregon.
Steve Cox is with Nikos Inc., Vancouver, Washington.
p&e
80 ieee power & energy magazine march/april 2020
book reviews an essential reference
a useful update of a classic text
TTHIS ISSUE’S “BOOK REVIEW” COL- cation flexible ac transmission systems to mid-2000s on the improved model-
umn discusses Power System Control (FACTS), such as static volt–ampere ing of gas turbines for both simple and
and Stability, third edition, written by reactive (var) systems. This new edi- combined-cycle power plants.
Vijay Vittal and James D. McCalley. tion covers all of these topics in new
This reviewer writes, “this new edition chapters. The structure of the book is The new material in the book is also
is a must-read for graduate students and well done and keeps the subject mat- very well done and matches the style
researchers and an essential reference ter flowing in a logical sequence. The and coverage of the traditional subjects
for all practicing engineers in the power chapters on the classic materials, such in the original text. The new chapter
and energy industry.” as the modeling of synchronous gen- on load modeling is a truly excellent
erators, excitation systems, and turbine addition and covers the most salient
Power System Control and governors, are still valid and of great technical developments in the last de-
Stability, Third Edition importance to both the student and cade relative to load modeling, which
practicing power engineer. These chap- has been led by the Western Electricity
By Vijay Vittal and James D. McCalley ters have all been updated to capture Coordinating Council’s Modeling and
Power System Control and Stabil- some of the new developments in these Validation Working Group (WECC
areas since the second edition of the MVWG), researchers at such organi-
ity is one of most widely used books in book. For example, the chapter on gas zations as the Electric Power Research
power engineering. I still own a copy of turbines provides new materials based Institute (EPRI), and Prof. Vittal him-
the original version of this classic text, on the work done at CIGRE in the early self at Arizona State University. Fur-
and I vividly recall it being one of the thermore, the chapter covers the basics
first books I read as a Ph.D. student of distributed energy resource model-
more than 25 years ago. Prof. Vittal and ing and how this is incorporated into
Prof. McCalley have done an excellent the aggregated load model.
job of updating this newly published
third edition. They have remained faithful Similarly, two new chapters pro-
to the spirit of the original text, written vide excellent coverage of some of
by Prof. Paul M. Anderson and Prof. the salient aspects of standard mod-
A.A. Fouad, while making significant els developed in the last decade,
updates of the original material and add- again primarily within the WECC
ing much-needed new information so MVWG, for modeling of static var
that the book remains an indispensable systems and renewable energy sys-
text and reference for the present-day stu- tems, with significant research done,
dent and practicing engineer. once again, at EPRI. The chapter on
FACTSs covers the modeling and dy-
Since the publication of the first edi- namic performance of thyristor–con-
tion, there has been tremendous change troller series capacitors.
in the industry, particularly in the are-
nas of renewable energy systems and An enhanced chapter on small-signal
load modeling and the increased appli- stability has been also included, which
is again important since an understand-
Digital Object Identifier 10.1109/MPE.2019.2954687 ing of such phenomena is critical for the
Date of current version: 19 February 2020 practicing power engineer. This chapter
82 ieee power & energy magazine march/april 2020
provides a solid basis for the fundamen- were well written with a good amount of is a must-read for graduate students and
tal aspects of power system oscillations. references and many well-presented ex- researchers as well as an essential refer-
amples and diagrams to help the reader ence for all practicing engineers in the
Two other welcome additions are grasp the technical details. Thus, I was power and energy industry.
new chapters dealing with voltage quite impressed by this update of Pow-
stability as well as power system pro- er System Control and Stability and do —Pouyan Pourbeik
tection and monitoring as they relate not hesitate to say that this new edition p&e
to system stability. Voltage stability
continues to be of critical importance
in modern power systems, and with the
advent of power electronic interface
generation, it is of utmost importance
for the practicing engineer to fully un-
derstand the mechanisms at play and
how controls must be properly tuned
The structure of
the book is well
done and keeps
the subject
matter flowing
in a logical
sequence.
and coordinated to ensure that voltage
control and stability are maintained
in the system. Another key aspect
of voltage stability studies is proper
load modeling, which is covered in
the comprehensive new chapter on
load modeling, as mentioned earlier.
Wide-area monitoring and protec-
tion systems are becoming increas-
ingly important on large power systems
around the world. To protect systems
from large-scale instability or cascad-
ing, many regions use special protection
systems that, for example, trip or curtail
generation when a certain element or
several elements in a critical transmis-
sion path are tripped due to a forced out-
age. Also, many regions now monitor, in
real time, the damping of critical modes
of oscillation of the system and use
monitoring data to assess the real-time
stability limits of the system. The new
chapter on power system protection and
monitoring covers many of the salient
points related to these important topics.
I thoroughly enjoyed reviewing this
book and found that all of the chapters
march/april 2020 ieee power & energy magazine 83
awards
IEEE Fellows
congratulations to the class of 2020
TTHE IEEE FELLOW AWARD IS A The Class of 2020 Fellows Luiz N. Barroso
special recognition for IEEE Members For leadership in analytical meth-
with extraordinary accomplishments in Congratulations to the following out- ods for power system economics and
IEEE technical fields. The total number standing IEEE Power & Energy So- regulation.
of recipients each year cannot exceed ciety (PES) members and to those
0.1% of the total higher-grade member- who were evaluated by PES for their Mohamed Benbouzid
ship, which ensures the exceptional sta- achievements. For contributions to the diagnosis and
tus of becoming a Fellow. fault-tolerant control of electric ma-
Jose Arroyo-Sanchez chines and drives.
Digital Object Identifier 10.1109/MPE.2019.2957551 For contributions to generation sched-
Date of current version: 19 February 2020 uling for electricity markets.
Sukumar Brahma Wei Qiao Hong Rao
For contributions to power system pro- For contributions to condition monitor- For leadership and contributions to the
tection with distributed and renew- ing and control of power electronics design and application of high-voltage
able generation. interfaced rotating machine systems. direct current in ac/dc grids.
Walter Mark Carpenter
For leadership in standards develop-
ment for power system protection.
Venkata Dinavahi PStAopITNhe!
For contributions to real-time simula-
tion of power systems with embedded Get Back to Your
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Sonja Glavaski
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John Harley power system analysis. Stop the pain of wasted time
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Jinghan He in Revit. Get back to what you want to work on.
For contributions to the protection of
substations and traction power. · Map Revit families and properties to EasyPower
Jan Izykowski equipment
For contributions to fault localization
in power lines. · Bring EasyPower analysis results back into Revit
Gerard Ledwich Autodesk EasyPower
For development of control of power
systems and power electronics. Revit Model System One-line
Yun Wei Li T-SCV
For contributions to power electronics 500 kVA
converters in microgrids and indus- .48-0.48 kV
trial drives. 4%
James McDowall T-SCV-S 3-#250, 1#250, 1-#3
For leadership in stationary battery .48 kV
standards and the energy storage in- .48 kV
dustry.
3-#1, 1#1, 1-#8 3-#350, 1#350, 1-#4 3-#1, 1#1, 1-#8
Amir-hamed Mohsenian-rad 3-#250, 1#250, 1-#6
For contributions to optimal resource
management in wireless networks and PANEL
the smart grid.
Analysis and
Pierre Pinson Auto-Design CURRENT IN AMPERES X 100 AT 480 VOLTS
For contributions to wind-forecast-
ing techniques in renewable energy .5 .6 .8 1 2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 100 2 3 4 5 6 7 8 9 1000 2 3 4 5 6 7 8 9 10000
integration. 1000 1000
TX-2 800 Automated
800 FLA Protective
600 600 Device
500 18.71 0.15 TX-2 500 Coordination
400 1 / 1.288 MVA 400
300 13.8 - 0.48 kV 300
6%
200 200
LV Momentary Report 100 TX-2 19.48 24.13BL-1 100
80 1000 / 1288 kVA GE AKR-50 80
EasyPower 10.4.0.198 10/11/2018 10:00:07 AM C:\...\Protection-1..dez 60 6% 1600/1760 60
EasyPower LLC 50 50
Comments: 40 SWG-4 BL-3 40
30 GE AKR-30H 30
800/400
20 20
ArcAFplapsrhoapnridatSehPoPcEk RReisqkuHirAaezrdcaArFpdlapsrhoparnd Shock Risk HazardEquipment Duties BL-1 17.58 1.90 10
10 GE MVT-Plus 8
Vpu = 1.00 8 Sensor = 1600 6
3 PHASE Fault TIME IN SECONDS Plug = 1600 5 TIME IN SECONDS
Total Fault Fault iate PPE RequiredEqui Type 6 Cur Set = 1.1 (1760A) M-1 4
5 LT Band = 1 3
LVPCB BL-5
LVPCB 4 STPU = 2.5 (4400A) C-H HFD 2
LVPCB 225/150
LVPCB
LVPCB
46’0.31-0.E’V4’0-q-A8”6u0L”i”IpDmFeOnRFctAlkaLNaNRrVlisc/Oaemhc-SmsrRmitahHtMrete2oiae:cdAcazdtMktaLeAsr1dHCSpdh8CYapAiBrziS-rpnt2oaoTpca3ruaEhdnrAncMoedhwdasCaach-Orrhe(AcyFNnrrecFacdItoFGeBlvadUyesVR:Eprh1302AqAi6a4’’s.I7-TuL4n.-n’0rB-0II86itceDOps)0”i”mdmN”oFeorOeOnvanRtNertcEdNLNnYrORaLakecFeitRmVrmaelgsMaldStey/isrtcAh:hicemcoLoSdtHcWve2SAkaedYaGzrpHtSaAa-p1Ta4lrplrE8dzopaMiBarnrodcoCc(haFuhOwceneNhdhdseFBa-nIryAGy:crU1ocR8vFAeAlaTr)sIiOhs rNIenmOciNdoeLvYendt Energy 3 ST Delay = Int
ST Delay I²t = Out
Sym X/R Mult Asym 2 Override = 50000A
Bus Name Bus kV Amps Ratio Factor Amps Duty Amps
19480.3 3.69 23188.3 1 BL-1 C-6 1
M-1 0.480 1.19 19480.3 .8 18627A 1 - 400 kcmil CU .8
MCC-1 0.480 20032.6 3.55 23640.9 20032.6 .6 BL-3 .6
MCC-2 0.480 1.18 19779.7 .5 GE MVT-9 .5
PNL-1 0.480 19779.7 3.43 23181.0 .4 Sensor = 800 .4
PNL-2 0.208 1.17 8882.5 .3
SWG-4 0.480 8882.5 3.73 10597.4 5961.4 Plug = 800
1.19 .3 Cur Set = 0.5 (400A) .2
5961.4 2.11 6377.3
1.07 LT Band = 1
24127.6 6.18 31990.4 .2 Inst = 4 (3200A)
1.33
LVPCB 24127.6 .1 TX-2 .1
.08 1000 / 1288 kVA .08
Short Circuit INRUSH
BL-5 .06
.06 Cutler Hammer Series C BL-3 .05
.05 HFD 29249A .04
.04 Frame = 225A (150AT)
.03 Trip = 150 .03
.02 BL-5 .02
20574A
.01 2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 100 2 3 4 5 6 7 8 9 1000 .01
.5 .6 .8 1 2 3 4 5 6 7 8 9 10000
CURRENT IN AMPERES X 100 AT 480 VOLTS
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march/april 2020 IEEE power & energy magazine 85
George Ridley Narasimham Vempati Yingjun Zhang
For contributions to stator core insula- For contributions to power system state For contributions to resource allocation
tion condition analysis in large hydro- estimation and transmission conges- and optimization in wireless commu-
electric generators. tion markets. nications.
Kevin Schneider Yan Zhang Xiao-Ping Zhang
For contributions to the development of For contributions to resource manage-
open access tools for distribution sys- ment in wireless networks. For contributions to modeling and the
tem analysis.
Yi Zhang control of high-voltage dc and ac trans-
Dipti Srinivasan For leadership in the development of
For contributions to computational in- real-time digital simulation in power mission systems. p&e
telligence for smart grids. systems.
& IAS march/april 2020
2020 PowerAfrica Conference
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86 IEEE power & energy magazine
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Illinois, United States, contact Carl Seg-
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Date of current version: 19 February 2020 neri, [email protected], http://
[email protected], https://
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Digital Object Identifier 10.1109/MPE.2020.2969674
in my view (continued from p. 96)
wires. The aluminum wires carry 98% weather conditions (high air temperature, To satisfy the reader’s curiosity about
of the electrical current. The steel core low wind speed, full sun). As shown by the alternatives, the dashed curve shows the
increases the conductor strength and solid curve in Figure 2, an ACSR or HT rating of a single larger Falcon ACSR
limits conductor sag under both high ice conductor with the same outer diameter [806 mm2 (1,590 kcmil), 54/19 strand-
and wind loads and at high temperatures (OD) produces a range of thermal ratings ing, 39.2 mm (1.545-in OD)] with a
(HTs). ACSRs are limited to continu- depending on the value of TCMAX. For thermal rating of 1,760 A at 100 °C
ous operation at about 100 °C or below Cardinal ACSRs (i.e., 54/7 stranding, due to its lower resistance (40% lower)
to maintain the tensile strength of the 483-mm2 aluminum area) at 100 °C, and larger OD. The dotted curve shows
hard-drawn aluminum wires. the thermal rating is approximately the thermal rating of a two-Cardinal
1,250 A. For Cardinal ACSSs (also ACSR bundle with twice the rating of
In my view, when designing new 54/7 and 483-mm2 aluminum area) at a single Cardinal conductor. The figure
overhead transmission lines at 345 kV 200 °C, the thermal rating is 1,900 A, makes it clear that higher line ratings
and below, HT phase conductors such approximately 50% higher. Both con- can be accomplished by using either a
as aluminum-conductor steel-support- ductors yield the same structural trans- large ACSR or a two-Cardinal bundle.
ed (ACSS) should be evaluated as an verse wind loads and offer essentially the In both cases, however, the line project
alternative to conventional ACSRs. same resistance per unit length. costs would be significantly higher due
With the same conductor diameter,
ACSSs can yield new lines with 50% IS YOUR REPUTATION FOR
higher thermal ratings and the same RELIABLE SERVICE AT RISK?
electrical losses at a capital cost typi-
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ACSR. The higher ratings avoid future Wildlife Power Outage Protection
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generation, distributed generation, and Material Will NOT Support Combustion
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HT conductors can be operated for
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tures between 150 and 250 °C with- Women Owned Business - WBENC
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to operate an overhead line at a higher P (801) 972-5400 | (888) 658-5003
TCMAX does not imply that a same-size Kaddas Enterprises, Inc. 2019. Not for Personnel Protection
HT conductor operates hotter than AC- www.KADDAS.com
SRs under normal system conditions or,
for extended periods of time, under emer-
gency conditions. The temperature of
the phase conductors in most existing
transmission lines is normally only
5–15 °C above air temperature since
system-normal power flows are typi-
cally much lower than the line’s thermal
rating and normal weather conditions
(i.e., higher cooling wind speeds and
lower air temperatures) produce lower
conductor temperatures than the worst-
case weather conditions assumed for
thermal-rating calculations.
An overhead line’s thermal limit is
equal to the phase conductor line current
that produces a conductor temperature
equal to TCMAX for an assumed set of
march/april 2020 ieee power & energy magazine 91
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Digital Object Identifier 10.1109/MPE.2020.2969735
to increased conductor material and la- this column, a simplified analysis re- two is simply that the aluminum wires
bor costs as well as the need for stronger garding the impact of replacing ACSRs in the ACSSs have been fully annealed
structures (e.g., use of a two-Cardinal with ACSSs of the same OD on project and maintain their electrical and me-
bundle doubles the conductor tension cost is instructive. Compare the main chanical properties at temperatures as
loads on strain structures). project costs for a new line using Car- high as 250 °C. The steel-core strands
As to the proven reliability of HT dinal ACSRs to those using Cardinal in ACSSs have a higher tensile strength
conductors, ACSSs are stranded with ACSSs. In this case, the aluminum and than those in ACSRs but are limited to
annealed aluminum wire layers instead steel strand sizes, OD, and steel-core di- 200 °C since they are conventionally
of full-hard aluminum wires and have ameter are the same for the two conduc- galvanized. The impacts upon line de-
been commercially available for ap- tors, and the compression connectors for sign are as follows:
proximately 50 years. Their use has Cardinal ACSSs can also be used with ✔ The resistance of the Cardinal
grown over that time, although they have the ACSRs. The difference between the ACSS is about 3% less than that
been used mostly for uprat-
ing existing lines. ACSS
compression connectors are
similar to normal two-stage
Bring your workconnectors for ACSRs but
are slightly longer. While
the tension in the annealed
aluminum layers of ACSSs
is quite low after installation,
there is no evidence that the
corona is different than that of
ACSRs with the same OD.
Other HT conductors are de-
scribed in the technical litera-
ture. Various HT conductor
types and their acronyms
are defined in CIGRE Tech-
nical Brochure 763. ACCC
(polymer-core), ACCR (met-
al-matrix core), (Z)TACSR
(zirconium aluminum), and
G(Z)TACSR (gap-type) con-
ductors all consist of alumi-
num wires (annealed or zirco-
nium alloy) over a steel, steel into focus
alloy, or composite core, and
any can be used in new lines,
but the cost is typically higher
than that of ACSSs. Their use
may make sense in certain Execute your work & asset management vision
compact or environmentally with precise tools and data
sensitive line designs. Simi-
larly, ACSSs are available with Work Orders 5G Small Cell
trapezoidal aluminum wires Routine Maintenance Streetlights
with much higher strength
steel cores (HS285) with mis- Crew Management Colocation / Joint Use
chmetal coating to enable op-
Estimates
eration at temperatures as high Compatible Units
as 250 °C. All these HT op-
tions should be considered in
a detailed line design analysis.
Although a detailed line
design is beyond the scope of Software that works
www.varasset.com
for the Cardinal ACSR (annealed ✔ For the same installed tension, the ✔ The maximum conductor ten-
aluminum conductivity is lower sag of the ACSS at 200 °C is about sion of the ACSS is slightly less
than that of full-hard aluminum). 5 ft more than the sag of ACSR at than that of the ACSR for the
✔ The weight per unit length is 100 °C in the same 1,000-ft span same ice/wind loading.
the same. (e.g., 40 versus 35 ft).
✔ The cost of the ACSS Cardinal
3,000Thermal Rating Versus TCMAX (35 °C Air, 0.91 m/s Wind, Full Sun) per pound is typically 10–20%
more than that of the Cardinal
Thermal Rating (A) 2,500 Two-Cardinal ACSR: the ACSR.
2,000 483 mm2 (994 kcmil)
1,500 Falcon ACSR: If the total new line project cost (ma-
806 mm2 (1,590 kcmil) terial and labor) breaks down as 30%
for conductors and 50% for structures
Cardinal ACSR, (see CIGRE Technical Brochure 638),
ACSS: 483 mm2 (954 kcmil) then the increase in cost due to the use
of the ACSS is approximately 2–3% for
1,000 conductor material and 5–10% for struc-
tures. The increase in total project cost
500 HT Conductor is less than 10%, and the increase in line
thermal rating is 50%. The cost of electri-
0 cal losses is essentially unchanged—3%
50 75 100 125 150 175 200 225 250 less for the ACSS than for the ACSR.
TCMAX (°C)
Summary
figure 2. Thermal rating versus TCMAX for three-phase conductor bundles of different
sizes with the smallest single-phase conductor at a range of maximum temperatures. The design of new overhead transmis-
sion lines should consider HT phase
ai157927777218_IEEE 2.pdf 1 17/01/2020 16:16 conductors since they can produce a 50%
increase in thermal line rating at an ad-
Make a difference to our ditional project cost of less than 10%.
ever-changing world Electrical losses in the line using either
ACSRs or ACSSs are difficult to predict
MSc Electrical Power Systems Engineering over the life of the line, but both conduc-
tors would produce the same energy
losses. Compression connectors for
ACSSs are essentially the same as those
for ACSRs and can be used with either
type of conductor.
The key advantage to using an HT
conductor is avoidance of potential fu-
ture power-flow constraints when relat-
ed to the line thermal rating. This added
robustness is available for a very modest
additional investment.
For Further Reading
Develop and build your career in the rapidly evolving power R. Gutman et al., “Analytical development
systems industry. Study part-time and completely online.
Join our next intake in September 2020. of loadability characteristics for EHV and
[email protected] UHV transmission lines,” IEEE Trans.
+44 (0)161 306 8333
manchester.ac.uk/powersystems Power App. Syst., vol. PAS-98, no. 2, pp.
606–617, Mar./Apr. 1979.
“Conductors for the uprating of ex-
isting overhead lines,” CIGRE, Paris,
Technical Brochure 763, 2019.
“Guide to overall line design,”
CIGRE, Paris, Technical Brochure
638, 2015. p&e
advertisers index The Advertisers Index contained in this issue is compiled as a service to our readers and advertisers: the
publisher is not liable for errors or omissions although every effort is made to ensure its accuracy. Be sure
to let our advertisers know you found them through IEEE Power & Energy Magazine.
Company page# URL Phone
ASPEN, Inc. CVR 4 www.aspeninc.com +1 650 347 3997
Bigwood Systems, Inc. +1 607 257 0915
CYME 6 www.bigwood-systems.com +1 800 361 3627
Delta Star +1 800 368 3017
DIgSILENT GmbH CVR 2 www.eaton.com/cyme
EasyPower LLC +1 949 900 1000
ETAP 84 DeltaStar.com
G&W Electric Company +1 770 495 1755
Hitachi T&D Solutions 3 www.digsilent.de/powerfactory
Hughes Brothers + 1 205 841 8600
Jeffrey Machine, Inc. 85 www.EasyPower.com/REVIT +1 801 972 5400
Kaddas Enterprises, Inc.
NuScale Power, LLC 13 etap.com/microgrid +1 800 722 8078
P & R Technologies
Powertech Labs, Inc. 89 gwelectric.com +1 217 384 6330
PowerWorld Corporation
PSCAD a product of MHI 15 www.hitachi-tds.com +1 773 338 1000
RTDS Technologies, Inc.
S&C Electrical Company 83 www.hughesbros.com +1 800 500 4SKM
Siemens AG +1 800 221 1311
SKM Systems Analysis, Inc. 19 jeffreymachine.com +1 844 873 6241
Tech Products +44 0161 306 8333
Trench Limited 91 www.KADDAS.com
University of Manchester
Varasset 20 www.nuscalepower.com
87 www.pr-tech.com
18 www.dsatools.com
10 www.powerworld.com
11 pscad.com
9 www.rtds.com
17 www.sandc.com
7 siemens.com/ruggedcom/cybersecurity
5 www.skm.com
14 www.TechProducts.com
21 www.trench-group.com
94 manchester.ac.uk/powersystems
93 www.varasset.com
YVI Labs 81 www.photonplusplus.com
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[email protected]
Digital Object Identifier 10.1109/MPE.2019.2954662
march/april 2020 ieee power & energy magazine 95
in my view Dale A. Douglass
Line Maximum Power Flow (MVA)transmission lines
designing for open access transmission
HHUNDREDS OF TECHNICAL PA- 1,000 Thermal Limit on Power Flow Independent of Length
pers were written prior to deregulation 800
in the 1990s regarding the optimization
of new transmission line designs. A 600 Power-Flow Power Flow Limited by
common goal was to minimize electri- Electrical Effects for
cal losses and capital investment in con- Limited by Long ac Lines
ductors, structures, and rights of way by
choosing the right conductor size with- 400 Thermal Power Flow Limit 25% of
in the boundaries of corona and electro- Rating for Thermal Rating for
magnetic fields. At the time, it was, to 1,000-km Line
some extent, possible to predict the line Shorter Lines
power flow (load shape and magnitude) 345-kV Transmission Line
for new lines at least 10–20 years into 200 Maximum Power-Flow
the future. Since the advent of open-ac- Dependence on Length
cess transmission, the development of 0
new power generation by wind and solar 0 100 200 300 400 500 600 700 800 900 1,000
sources, the sometimes rapidly shifting Line Length (km)
fuel costs (i.e., gas versus nuclear and
coal), and environmental restrictions on figure 1. Power-flow limits as a function of line length at 345 kV (adapted from
conventional generation, it is no longer Gutman et al.).
possible to predict the line-load magni-
tude and daily load shape for most new Power flow on overhead lines is lim- found in the form of electronic devices
lines over their expected design life of ited by electrical effects (e.g., voltage (e.g., flexible ac transmission system
40 years. drop and phase shift) and by the maxi- devices) or phase-shifting transform-
There has been a major shift in trans- mum temperature allowed for the phase ers. In many lines, however, one comes
mission expansion planning away from conductors (TCMAX). Voltage drop and up against the thermal limit (rating) of
deterministic methods, as discussed at phase shift increase with length; thermal the line at its maximum design tem-
length in the July/August 2016 issue of rating does not, as shown in F igure 1. perature. The physical limits due to
IEEE Power & Energy Magazine. In Therefore, short lines are limited ther- such factors as electrical clearance and
that issue, several articles explained the mally, and long lines are limited elec- conductor system aging are not easily
difficulties in predicting system power trically unless compensated. Power changed in an existing line.
flows that were increasingly uncertain. flow on extrahigh-voltage (EHV) and
In addition, the daily loading patterns ultrahigh-voltage lines may also be More than 80% of existing transmis-
(capacity factor) that new overhead indirectly constrained by the thermal sion lines around the world use alumi-
lines will experience are more difficult rating of HV lines due to load reliabil- num-conductor steel-reinforced (ACSR)
to predict, especially where wind is the ity (N-1), postcontingency overloading phase conductors. ACSRs consist of two
primary generation source. of the parallel EHV lines, or the use of or more layers of hard-drawn aluminum
lower-voltage lines. wires, helically stranded around a core
Digital Object Identifier 10.1109/MPE.2019.2954688 of concentric, helically stranded steel
Date of current version: 19 February 2020 In recent years, many of the solu-
tions to these power-flow limits can be (continued on p. 91)
96 ieee power & energy magazine march/april 2020
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