AbstractPioneering efforts in showing how electricity energy storage can be a valuable asset in a Smart Grid Distribution System have been in process for the last few years. Several demonstration projects were completed to show how substation loading could be controlled and managed to delay upgrades. The next step was to show how the load deferral benefit could be combined with distribution circuit automation to use battery storage as a system reliability enhancement tool. This presentation provides an overview of how the systems function to allow the batteries in a substation to allow portions of a network to function as an island power system.

Index Termsenergy storage, smart grid,

islanding operations, PCS.

I. INTRODUCTION HIS panel session covers the role of energy storage in smart grids. Building a true utility smart grid goes way

beyond adding advance metering services to every home and business. Adding intelligence in the substations and distribution circuits is equally important. Over the last four years American Electric Power (AEP) and the S&C Electric Company have worked to deploy several demonstration projects that show the value of distributed storage in the grid. The first project in 2006 was a deployment of a 1.0 MW, 7.2 MWh sodium-sulphur battery to peak-shave the summer load on a 20 MVA transformer and delay the substation upgrade for three-five years until firm load growth showed the need. The project proved successful and showed that large-scale batteries were a viable solution for load management. Figure 1 shows how the load peaks were managed during peak load conditions. ____________________

B. P. Roberts is with S&C Electric Company, Franklin, Wisconsin (email: broberts@sandc.com).

FIGURE 1

LOAD MANAGEMENT WITH DISTRIBUTED BATTERY STORAGE

II. UTILIZING DISTRIBUTED STORAGE FOR RELIABILITY IMPROVEMENT

In 2007 AEP launched additional projects to show how distributed storage could improve system reliability and reduce customer outage minutes, as well as control loads. This process is called islanding a portion of a local grid and powering it from a local source.

The ability to island is of great benefit because the restoration process can be time consuming. Several challenges encountered in the restoration process include: assembly of restoration crews regardless of time of day, location of the fault, which can be extremely difficult because electric lines may stretch for several miles and then the actual repair and restoration to service of 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 several hours. Islanding creates the ability to have most, if not all, of those customers served by a local source while the restoration effort is ongoing. This and several other benefits can be realized from islanding.

AEP selected three distribution areas in three states as candidates for deployment of 2.0 MW, 14 MWh sodium-sulfur (NaS) batteries to show the value of islanding to improve system reliability. Figure 2 shows one of the battery system installations that have been functioning in the grid since the summer of 2009.

FIGURE 2

Deploying Battery Energy Storage in the Utility Distribution Grid

Bradford P. Roberts, P.E., Life Senior Member, IEEE

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978-1-4244-6551-4/10/$26.00 2010 IEEE

2.0 MW SUBSTATION BATTERY WITH ISLANDING CAPABILITY

Each of these sites combined the battery with a set of intelligent switches in the network down-stream of the substation containing the battery. Upon loss of the transmission service to the substation, the battery system controller and the intelligence in the distribution switches know the amount (kVA and kW) of load in each circuit and the condition of each load feeder. Based on this data at the time of the service loss, the battery controller can initial a re-powering of the down-stream island load. Restoration of service occurs within a few seconds with as many circuits possible based on the load prior to the service loss. Once crews restore service to the substation the battery controller re-synchronizes the island load with the source and restores normal utility service in a seamless fashion.

III. THE NEXT STEP IN DISTRIBUTED ENERGY

STORAGE The deployment of battery storage systems in the

distribution grid have shown an improvement in system reliability is possible. The next step is adding stored energy even closer to the load may have even greater value. In the recent U.S. Department of Energy Energy Storage Demonstration Stimulus Awards, funding was provided to show how localized storage packages deployed in the low-voltage utility grid could provide even greater benefit to a smart grid system.

This concept is called Community Energy Storage (CES)

and is based on deploying small pad-mounted battery energy storage units in residential neighborhoods to cope with customer loads, roof-top photovoltaic systems and eventually the impact of Plug-in Hybrid Electric Vehicles (PHEVs) on utility demand. These factors present a lot of unknowns for future utility load forecasting. Large concentrations of PV roof systems could disrupt utility voltage control as clouds pass through an area of high PV concentration utilities with large amounts of small CES units (typically 25 kW each) could be controlled collectively to react the same as larger systems installed in substations.

IV. CONCLUSION The future of distributed storage will play a major role in

smart grid development. The size of these systems and their point of deployment in the grid will depend on the unique requirements on a case-by-case basis.

V. BIOGRAPHY

BRADFORD P. ROBERTS (M-1966, SM 2005) holds a BSEE from the University of Florida. Mr. Roberts is currently employed with S&C Electric Company in the Power Quality Products Division.

Mr. Roberts has held senior management positions in two of the

major UPS manufacturers during his career. Brad has published over 40 technical papers and journal articles on critical power system design and technology.

He is a past chairman of the IEEE Power Engineering Societys

Emerging Technologies Coordinating Committee, current Executive Director of the Electricity Storage Association and a member of the CIGRE Working Group C6.15 Electricity Energy Storage Systems. He is the 2004 recipient of the John Mungenast International Power Quality Award and 2009 recipient of the Phil Symons Electricity Storage Award.

NAS Battery Station

Two 1 MW NAS Units

PCS Transformer

Genset

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