Almacenamiento de energía y control mediante SCADA

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50 IEEEpower & energy magazine march/april 2010

significant improvement with the addition of distributed

intelligence in conjunction with multiple-MVA/multiple

MWh batteries for energy storage located in or near utility

substations.

Islanding for Improved ReliabilityIslanding is a scheme on the electric grid to isolate and ener-

gize sections of the grid with a local energy source in the event

of a power outage. This energy source may be from a fossil

fuel supply or from advanced technologies such as fuel cells

or energy storage batteries. The ability to island is extremely

beneficial when power from utility supply is lost, typically dur-

ing natural disturbances or when a fault occurs on the electric

system. This ability improves reliability and ensures that cus-

tomer service interruptions are kept to a minimum.

This islanding benefit is of significant value to the electric

utility, especially in areas with frequent electrical outages.

Areas that will benefit considerably from islanding include

load centers fed by old, long lines

areas with dense vegetation (vegetation can come in

contact with electric lines and may cause interrup-

tions)

locations subject to frequent natural disturbances like

tornadoes and storms.

The ability to island is of great benefit because the res-

toration process can be time-consuming. The challenges

encountered in the restoration process include assembling

restoration crews regardless of time of day; locating the fault,

which can be extremely difficult because electric lines may

stretch for several miles; and actually repairing and restor-

ing to service the faulted electric service line or component.

While this extensive process is taking place, the customers

being served by that electric service line are without power,

sometimes for many hours. Islanding, however, creates the

ability to have most if not all of those customers served by a

local source while the restoration effort is ongoing. There are

other benefits that can be realized from islanding as well.

The Islanding Value PropositionReliability data are of great significance to the electric utility,

as they help gauge its ability to provide consistent and depend-

able service to its customers. These data are taken into account,

and plans are made to improve service to areas considered

deficient. In addition, electric utilities are required to provide

electric service reliability data to their respective public utili-

ties commissions (PUCs). This enables PUCs to pressure utili-

ties to improve service reliability. Thus, it is imperative that

utilities maximize reliability across the electric grid.

Numerous benefits accrue from the ability to intelligentlyisland sections of the grid when a fault occurs, including

those listed here.

Improved reliability indices: Reliability indices

such as the customer average interruption duration in-

dex (CAIDI) and system average interruption duration

index (SAIDI) are standard measures of reliability

used to determine the dependability of electric util-

ity service. Islanding can significantly improve these

indices, as fewer customers will be without power and

service interruptions will be shorter.

Resource optimization: Islanding allows prioriti-

zation of the restoration process by allowing limit-ed human and physical resources to concentrate on

nonislanded areas first. Islanding will save human

and financial resources, as crews may not need to

be dispatched to islanded regions during nighttime

hours and paid higher overtime rates. Depending

on the nature of the outage, they may be able to

handle the restoration as part of their normal daily

schedules.

Capital deferral: Islanding can provide an im-

mediate fix for a problematic network and allows

traditional solutions (station construction and/or

enlargement, transmission extension, and distribu-

Station

Energized

Disconnected

figure 1.ADI.

Station

Station

Low Load: Feed All Loads

Energized

Disconnected

figure 2.Selection of individual customer loads athigh-load periods.

Station

Zone 2Zone 1

figure 3.DDI.


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march/april 2010 IEEEpower & energy magazine 51

tion feeder enhancement) to be deferred until the

grid can be redesignated to alleviate the problems.

Approaches to IslandingGiven the benefits from islanding outlined above, the ques-

tion becomes, What is the most practical way to actually

achieve islanding? In analyzing a number of ways to pro-

ceed in order to solve several specific issues affecting three

applications where islanding of stored energy might actu-

ally be justified, AEP considered two distinct load manage-

ment methodologies for achieving islanding of distributed

resources. These are 1) adaptive dynamic islanding (ADI)

and 2) discrete dynamic islanding (DDI).

Adaptive Dynamic IslandingADI relies on the utilitys ability to turn on or turn off indi-

vidual customer loads remotely through the use of advanced

metering infrastructure (AMI). Once AMI is sufficiently

deployed, the adaptive approach to dynamic islanding willbecome reasonably practical in terms of implementation and

control (see Figures 1 and 2).

The promise of ADI is that, given sufficient development

and deployment of AMI technology, the utility will be able

to treat each customers load as an island. Once a sufficiently

high level of AMI penetration is reached, every customers

electric meter will be able to be controlled remotely. Thus

certain critical loads such as hospitals, police stations, and

firehouses could be given priority in the event of electrical

power outages. In similar fashion, it would be possible for

less-critical customer loads to be cycled during the inter-

ruption in order to share the available power and socialize

the benefits from islanding while spreading the inconve-

nience of interruptions equitably within the island.

Figure 1 illustrates conceptually how the battery man-

agement system could selectively de-energize or cycle some

customer loads while ensuring higher-priority services

remained energized as long as possible.

Figure 2 illustrates how the ability to remotely connect and

disconnect individual loads will let the energy storage system

intelligently manage the load being supplied in order to opti-

mize the size of the island being served while respecting the

magnitude of stored energy available. Islanding could essen-

tially eliminate interruptions from outages that occur dur-

ing off-peak times, while service interruptions at peak timeswould be mitigated, depending on the duration of the outage.

In the ADI scheme it would be very simple to adjust the

number of customers connected based on the total available

energy in the battery.

At low-load times, the batterys capacity would be ade-

quate to energize the entire section of grid in the island. For

Milton Substation13834.5 kV, 25 MVA

Balls Gap Feeder34.5 kVSummer 200513.7 MVACustomers = 3,204

Grassy Fork Substation13834.5 kV, 25 MVA

Grassy Fork Feeder34.5 kVSummer 200513.7 MVACustomers = 2,950

Future Multiphase Tie toGrassy Fork/Yawkey FeederOnce New Station Exists

Potential AutomatedSectionalizing Points

Rough Path for 8 mi, 138 kV SpurRequired to Feed New Balls Gap Station

Potential or ExistingRecloser Locations

Milton/Grassy Fork Feeders

Selected Site forBalls Gap Station;DESS Location UntilNew Sub Is Completed

figure 4.Balls Gap/Grassy Fork feeder one-line diagram.


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situations in which the battery could not energize the entire

section, however, select loads would be energized and/or

cycled as depicted in Figure 2.

Since the penetration of AMI devices was not sufficient

to allow implementation of ADI (at least in the areas where

it could potentially be justified), AEP looked for a practical

alternative to provide the needed level of load control over a

section of the network.

Discrete Dynamic Islanding

DDI describes the ability to connect and disconnect dis-creet sections or zones of the grid (feeder sections) instead

of individual customers, as in the ADI scheme described

above. Thus, each section of the grid that becomes islanded

will include several residential and/or commercial buildings.

This type of islanding is made possible through the use of

advanced communication and control systems that employ

distributed intelligence spread among the feeders sectional-

izing and protective devices that then communicate directly

with each other to automatically isolate faults and restore

service to unfaulted line sections. This method of island-

ing proved to be easier and quicker to implement, as the

core technology and the requisite hardware were currently

available. AEP decided to implement this method in order to

more quickly evaluate the benefits of islanding technology

as a whole. It is also of interest to note that DDI would only

tend to complement ADI if and when the requisite AMI tech-

nologies are in place. Both methods effectively accomplish

the goals of islanding for faults upstream of the island, but

DDI is mandatory if islanding is to be supported during any

faults that occur inside the island. Only DDI has the inherent

ability to detect and automatically isolate faults.

Figure 3 shows the discrete (zonal) approach to load con-

trol and management based on total load in each feeder sec-tion at the time of an outage and the magnitude of stored

energy available from the battery. These two variables are

managed based on the projected time for feeder restoration.

The balance of this article will focus on the practical

application of islanding and look in detail at the islanding

technology selected. AEP implemented three projects to

evaluate the practical benefits of islanding. The details of

one of the projects, the Balls Gap feeder, will be discussed.

Overview of Islanding ProjectsFor each site AEP selected a multi-MW sodium sulfide (NaS)

battery as the stored energy source. The sites are distributed

Not IntelliTEAM

Milton Station

IntelliTEAM

1

63 A120

F8 F9

SW663 A63 A63 A

SW363 A63 A63 A F2

52 A11

F4000

F3000

F1

SW411 A11 A11 A

SW511 A11 A11 A

F57 A522

SW24 A4 A4 A

SW83 A3 A3 A

F73 A330

F61 A523SW7

0 A0 A0 A

SW10 A0 A0 A

0 A1202

Balls Gap DESS

Single PhaseReclosers

Logo Copyright AEP.Columbus. OH

Note: When src side field

is source color and Ld side fieldis gray, it indicates one phase

of recloser has opened.

651 R

651 R

figure 5.Balls Gap feeder one-line diagram.

Islanding is a scheme on the electric grid to isolateand energize sections of the grid with a local energy sourcein the event of a power outage.


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march/april 2010 IEEEpower & energy magazine 53

over AEPs service territory and are located respectively in

West Virginia (Balls Gap), Ohio (Bluffton), and Indiana (East

Busco); the sites share the common characteristic that the

feeders where the batteries are to be deployed are all radi-

ally fed, with no readily accessible source of alternate supply.

Each battery is rated for 2 MW at 7.2 MWh, indicating that

the battery can supply 2 MW of power for up to seven hours,

assuming the battery is fully charged at the time of an event.

This also indicates that the feeder devices to be used for the

islanding are located so as to carve out a 2-MW block of load,

with additional smart switches added to allow the island-

ing scheme to shed load once islanding has occurred for long

enough to partially deplete the energy in the NaS battery.

The feeder devices incorporated into the various island-

ing schemes include intelligent sectionalizing switches in

addition to two popular intelligent electronic device (IED)

reclosers. And while the distributed automation (DA) scheme

selected has been performing well for over a decade, its use

for islanding does represent new tech-nology and the chance to learn how DA

devices perform in new applications.

In view of the pioneering aspect of

these projects, an in-depth study of each

islanding application was undertaken to

investigate various technical challenges

associated with the use of NaS technol-

ogy and recommend measures to deal with

each challenge. Included in the studies

were in-depth coordination studies, load-

ing and historical fault data analyses, and

feeder modeling to verify islanding perfor-mance under real-world scenarios.

Balls Gap (West Virginia)Islanding ProjectOf the three projects undertaken by

AEP in 2009, the Balls Gap project was

the most complex. For this particular

application, there were various obstacles

to using stored energy to mitigate service

interruptions that had to be dealt with in

an extremely challenging environment.

The Balls Gap feeder includes a roughly35-mile-long, 34.5-kV overhead radial

feeder that runs through the Appalachian

Mountains southeast of Milton, West

Virginia, where the distribution substa-

tion is located (see Figure 4).

Since this is a radially fed circuit with

no possible ties to an alternate source, per-

manent outages tend to last for hours, given

the many challenges of getting resources

to the area. But an analysis of loading and

historical fault data indicated that the vast

majority of faults that resulted in a lock-

out of the breaker occurred upstream of the first recloser

shown above and that roughly 2 MVA of load exists below

this recloser. Since this fairly closely matched the size of the

batteries AEP was planning to install, the Balls Gap feeder

began to come into focus as an appropriate candidate for

evaluating the costs and benefits of applying NaS technology

for islanding purposes.

Although no alternate three-phase connection other than

the Milton station is available, small single-phase links to

similarly sized single-phase lines served from the Grassy

Creek station do exist. The long-term plan is thus to bolster

the stability of service in the entire region by installing a new

station and upgrading the stringy single-phase lines to three-

phase trunks that will connect the new Balls Gap station to

the existing station at Grassy Creek. In addition, eight miles

of 138-kV transmission line will have to be run, again through

the rolling mountains that saturate the area. With siting,

acquisition of rights-of-way, and construction planning, the

(d)

(a) (b) (c)

figure 6.Feeder devices involved in islanding: (a) smart DA switch withIED control Networking radio, (b) recloser A IED control, with modulenetworking radio, (c) recloser B IED control, with module networking radio,and (d) PCS (interior view showing power electronics and system controls).

(Images courtesy of AEP).


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transmission spur is a four-to-five-year effort under normal

planning horizons, during which time the customers servedfrom the Balls Gap feeder would see essentially no relief from

the lengthy interruptions that typically occur when a perma-

nent fault takes the Balls Gap feeder breaker to lockout.

During the site preparation, the Balls Gap feeder was

analyzed to determine the number of and locations for feeder

devices that would work together to create and maintain the

island during periods when the battery becomes isolated from

the Milton station by an upstream fault. A simplified one-

line diagram showing the portion of the feeder that includes

the 2 MVA of customer loads intended to benefit from the

DESS is shown below in Figure 5. Six feeder devices (two

reclosers and four sectionalizing switches) were deployedat crucial locations in order to apportion the total load into

logical groups with roughly equal demands.

For faults upstream of the first automated feeder device

(Sw-3), all of the downstream devices will open on loss of

source (LOS) and report this to the other devices. Knowing

that all of the DA devices are open, the module at the power

conditioning system (PCS) will close Sw-1 to energize

the first section of line to Sw-7. Knowing that all devices

opened on LOS, the DA scheme has only to quantify how

much load is being picked up as each line section is ener-

gized relative to how much capacity the NaS battery was

telling the interface module it could supply when the eventfirst began. The DA scheme keeps track of this capacity as

the transfer progresses, ensuring that the capacity of the

NaS battery is never exceeded.

For faults that occur within the island, so long as the fault

does not occur in the line sections between the DESS and the

main trunk of the circuit (between Sw-1 and Sw-4 and Sw-5),

the DA scheme will automatically isolate the fault and restore

service either from the DESS or from the Milton substation,

depending on the faults exact location. In this scenario it is

important to note that the Milton substation will continue to

serve as much of its normal load as possible, something not

previously possible for faults this far out on the feeder. This

functionality is unique to the DDI approach and leverages

the ability of the distributed intelligence of the DA scheme to

derive added benefit from the islanding technology.

A variety of smart feeder IEDs were incorporated into the

open-architecture DA scheme over the three distinct island-

ing projects, as is illustrated in Figure 6. These included the

power conditioning system (PCS) used to convert the NaS

battery energy to AC power suitable for injection into the util-

ity grid.

Commissioning of each of the DESS islanding applica-

tions was performed by AEP by bypassing each of the feederdevices and then simulating an LOS from the normal feed of

supply. For each site, the loss of source voltage was simu-

lated to test system performance. The planning engineer for

the Balls Gap project, however, wanted to get an even higher

level of confidence that the scheme was ready to work. A test

was formulated whereby at a designated time a load break

switch just ahead of the island would be opened to create an

actual LOS scenario. The test went precisely as planned, and

the NaS battery picked up all the customers in the island. The

final system installation is shown in Figure 7.

ConclusionsIn actual operation, the system at Balls Gap did require minor

adjustment in the sensing circuits to ensure proper coordina-

tion of the reclosers and automated feeder switches. Actual

islanding events have occurred with successful operation of

the batteries in islanding mode. Based on the three projects

discussed in this article, AEP has undertaken an even larger

project to be completed in 2010.

For Further ReadingA. Nourai and C. Schafer, Changing the electricity game,

IEEE Power Energy Mag., vol. 7, no. 4, pp. 4247.

B. Roberts, Capturing grid power, IEEE Power EnergyMag., vol. 7, no. 4, pp. 3241.

A. Nourai. (2009, Nov. 1). Utility-scale energy storage

migrates toward the grid edge [Online]. Available: www.

tdworld.com

BiographiesAli Nourai is the manager of energy storage programs at

AEP and chairman of the board for the Electricity Storage

Association.

David Kearnsis application director, smart grid technol-

ogies, for the Automated Systems Division of S&C Electric

Company. p&e

figure 7.Balls Gap energy storage system installation.(Photo courtesy of AEP.)

DDI describes the ability to connect and disconnectdiscreet sections or zones of the grid (feeder sections)instead of individual customers.

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Almacenamiento de energía y control mediante SCADA