Case studies from operation of a nationwide PQ&R ...

NDUSTRIAL AND COMMERCIAL ELECTRICITY CONSUMERS

are increasingly impacted by poor power quality and reliability

(PQ&R). A utility distribution system fault, even hundreds of miles

away, can cause widespread voltage sags that shut down susceptible

process equipment [1]. Correlating process interruptions with voltage disturbances

requires prompt notification of such PQ&R events. Effective communication with the

utility company and assessment of mitigation equipment options are greatly facilitated

when local historical PQ&R data are available, but only if the information is put in a

form that the customer can act on.

A Web-based, near real-time PQ&R monitoring system is continuing to

be put in place to provide such information, both locally and on a

nationwide basis [2]. Low-cost monitors record PQ&R event char-

acteristics and, using an internal modem, transmit event data

via the Internet to a central database. The database servers

are a component of the system, and no additional hardware

or software is needed by the end user. The monitor system

infrastructure, shared by all monitor owners, provides capa-

bilities for data aggregation and display, e-mail and pager

notification, site administration, and summary reporting of

the data using a Web browser.

The system provides real-time notification of PQ&R events

at single or multiple facilities and access to statistical informa-

tion and trends related to PQ&R events as well as voltage regulation

and imbalance. A principal goal is deployment of a vast network of moni-

tors, which cannot be accomplished unless the monitors are affordable and the infra-

structure is scalable.

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1077-2618/05/$20.00©2005 IEEE

Case studies from operation of anationwide PQ&R monitoring system

B Y W I L L I A M E . B R U M S I C K L E , D E E P A K M . D I V A N ,

G L E N A . L U C K J I F F , J O H N W . F R E E B O R G , & R O G E R L . H A Y E S

I

© DIGITALVISION, LTD.

The monitor system architectureallows deployment of thousands ofmonitors at industrial, commercial,government, and utility sites at rea-sonable cost. In cooperation with theU.S. Department of Energy (DOE),utilities, and leading manufacturers,the deployment of system monitorsis underway, with a target deploy-ment of over 50,000 nodes across theUnited States and Canada.

This article briefly reviews thesystem architecture and presentsselected case studies from the firstyear of system operation, focusinghere on industrial sites.

Web-Based Monitor System OverviewThe end-to-end system comprisesthe many deployed monitors, the public telephone sys-tem, the existing nationwide network of local Internetpoints of presence (POPs) that bridge the gap betweenthe telephone lines and the Internet, the Internetitself, the monitor system servers and database, andfinally, the end user’s Web browser. The low-cost mon-itors function only as an integral part of the monitorsystem, in which much of the intelligence is placed onthe system servers. This allows for advanced dataanalysis, display, and aggregation capabilities, whileminimizing the cost per monitoring node.

These monitors record both time stamped PQ&Revent data and 10-min average rms voltages. An inter-nal modem, together with a long-life rechargeable bat-tery, allow the monitors to communicate data over theInternet with the central data-base servers, even during powerinterruptions. Immediately fol-lowing data upload, the centralservers e-mail event summarynotifications to user-designatedaddresses. Commonly available“e-pager” services can forwardthese messages to alphanumericpagers or text-capable mobilephones. The e-mail text includesa direct Web link (URL) to viewdetailed event waveforms on thesystem Web site. Both recent andhistorical data can be viewed atany time from any Internet-con-nected PC using popular Webbrowsers.

All system monitors are regu-larly synchronized with the cen-tral server, which is itselfsynchronized to NIST Coordinat-ed Universal Time (UTC). Eachmonitor can record voltage sagsand swells, brownouts, over volt-ages and sustained interruptions.

It also has limited capability for tran-sient monitoring. Available monitorscan directly monitor single or three-phase voltages at 120, 120/208 or480 V; 15-kV class (or higher) moni-toring is accomplished using externalpotential transformers. Detailed sys-tem and monitor specifications weredescribed in an earlier paper [2]. Themonitor firmware is stored in flashmemory and can be automaticallyupgraded as system improvements aredeveloped. Nonvolatile event datamemory is cleared after confirmationof successful data upload to the cen-tral database.

The end-to-end system is opera-tional in the United States and Cana-da. A limited number of monitors inSingapore, Malaysia, Australia, and

Brazil have verified the potential extension of thisWeb-based system to a worldwide monitoring network.

Monitoring System Case Studies A prototype end-to-end PQ&R monitoring systembegan operating in February 2001, with approximately30 monitoring nodes distributed around the UnitedStates. More than 10,000 event reports were transmit-ted to the alpha system database and Web server. Thesystem monitors are now in normal production. Morethan 600 production monitors were shipped in 2002,and more than 1,100 units are now operating in 47states. More than 30,000 PQ&R events were reportedin 2002 alone; that total increased beyond 250,000events by mid-2004.

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Single-phase monitor’s 320-min periodic rms voltage report (June 2002): Maximum

(top) and minimum (bottom) single-cycle rms voltage per 10-min period, immedi-

ately following installation.

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CONSUMERSAND THE UTILITY

COMPANIES THATSERVE THEM

NEED ACCESS TORELEVANT ANDTIMELY PQ&R

INFORMATION.

Here, we discuss actual casestudies from the productionmonitoring system. Precise datesand locations are omitted toassure monitor owners’ anonymi-ty. Voltage profile and waveformfigures are identical to those onthe system Web site, but arereplotted here for improved reso-lution in print.

Tracing Facility PQ Problems

Facility Wiring ProblemPQ problems range from theoccasional voltage sag to ongo-ing, yet intermittent, voltagevariations. In one case, buildingtenants were experiencing con-tinuing equipment failures onsingle-phase lines. In June 2002,the utility company installed amonitor at several locationsthroughout the building. Severalvoltage swell and voltage sagevents were captured, yet themore telling information camefrom the periodic root-mean-square (rms) reports , whichshow the maximum and mini-mum rms voltages recorded ineach 10-min period throughoutthe day. Figure 1 shows a period-ic rms report over one five-hourperiod. Wide variation in voltageis evident.

From these reports, the utilityengineer narrowed the cause toeither a defective utility voltageregulator or a neutral bondingproblem at the site. Subsequentinvestigation showed that a looseneutral wire connection at thesite was the root cause of thesevoltage variations. A monitorsystem upgrade in October 2002added 10-min average rms volt-age measurements to the period-ic rms records; these can besummarized to provide utilityservice voltage regulation andimbalance reports.

Utility Voltage Regulation ProblemA company running a seasonal24/7 process installed monitorsafter experiencing repeated equip-ment shutdowns over severaldays. Periodic rms records, exem-plified by Figure 2, showed thatthe utility supply voltage, nomi-

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Three-phase monitor periodic rms voltage report: maximum (blue) and minimum

(red) single-cycle rms voltage per 10-min period.

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Normalized PQ&R event severity density, for 32 large industrial plant monitors, over a

two-month period of 2002.

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Decreasing Duration (in Cycles)

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nally 480 V, varied from under 460 to over 530 Vthroughout a period of many days.

The facility engineer used this information to nego-tiate with the utility company, which subsequentlyrescheduled local substation maintenance to improvevoltage regulation during the peak processing season.

Multiple-Facility PQ&R StatisticsManagement of information on facility power systemsstatus and history at multiple locations is simplifiedusing a PQ&R reporting system with a central data-base and Internet-wide access. A number of companieswith multiple facilities, many with dual feeds at trans-mission or subtransmission voltage, are using thismonitor system. In those cases, a 120 V three-phasesystem monitor is connected to the preexisting serviceentrance potential transformers (PTs); the monitor pre-sents less than 6 VA of load per channel to the PTs. Amajor manufacturer has installed over 100 monitors inthis manner at its facilities across the United States

and Canada, on its way to monitoring all of its NorthAmerican facilities. Both local and corporate facilitymanagers, as well as the local utility companies’account managers, receive pager notification when aPQ&R event occurs. The notification address list isdistinct for each monitor site, and the notification cri-teria can be set separately for each address.

Data from 32 monitors at large U.S. industrial sitesover a two-month period is normalized and plotted in

TABLE 1. VOLTAGE SAG EVENT SUMMARY DATA(SUMMER 2002).

Worst Case RMS Channel Min. as % of Nominal

1 72.8 V-rms 60.6%

2 74.2 V-rms 61.9%

3 35.3 V-rms 29.4%

(a) Voltage waveform around event start (Summer 2002). (b) Cycle-by-cycle rms voltage profile during sag event.

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Event 1695 Detail (4 November 2002). (a) Voltage waveform. (b) RMS “voltage profile” or similar.

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I–Grid Power Quality Event

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Figure 3 to demonstrate the relative density of therecorded voltage sag severities. It is evident that shortduration shallow voltage sags are by far the mostprevalent PQ&R events at these sites. This is in keep-ing with the basic results of the Electric PowerResearch Institute (EPRI) Distribution Power Quality(DPQ) Study [3] and the Canadian National PowerQuality Survey [4]. Such site-specific statistics can

help guide corporate investmentin cost-optimal mitigationequipment, whether a backupgenerator, flywheel or batteryUPS, or dynamic voltage sag cor-rection device.

Individual Large Industrial PlantMonitoringInformation on a specific eventfrom one multimegawatt manu-facturing site is provided inTable 1. Figure 4(a) and (b)shows the voltage waveform atthe start of the voltage sag eventand the rms voltage prof i lethroughout the event. Thereported event duration is 13.8cycles (230 ms). It is apparentfrom examination of Figure 4(b)that the utility system fault thatcaused this sag was cleared afterfour to five cycles (70–80 ms),yet restarting of large loads onthe system kept the voltage sup-pressed for nine cycles (150 ms)more. The abrupt return to near-

nominal voltage following a voltage sag is known tohave damaging effects on motors and many powersupplies [5].

Recorded waveform data spans four cycles aroundthe event start time, one cycle before the detected starttime and three cycles after, and another four cyclesaround the event end time, two cycles before and twocycles after. Events shorter than six cycles duration are

TABLE 2. EVENT LOG FOR WISCONSIN, 4 NOVEMBER 2002, AROUND TIME OF PLANE CRASH.

Moni- Event Worst Case Worst Case tor # ID Local Time Event Type Duration RMS Voltage % of nominal

1 111 11/4/2002 5:35:31 PM Instantaneous Sag 5.8 Cycles 101.3 84%




4 2980 11/4/2002 5:35:32 PM Instantaneous Sag 1 Cycles 104.4 87%











MAG-DUR plot of all I-Grid events recorded over six months in 2002 at a major man-

ufacturing location.

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PQ EventsITI/CBEMA-LowerDySC-EO 53 Aggregated Events

Magnitude Versus Duration

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captured in their entirety. Figure 5(a) shows such ashort event voltage waveform.

The ability to review historical data is critical forevaluating cost-effective solutions to PQ&R problems.Figure 6 shows a “MAG-DUR” scatter plot from theWeb site, covering all events recorded in a six-monthperiod at a major manufacturing plant. These datainclude the voltage sag event of Figure 4. For eachrecorded PQ&R event, one point is plotted for theworst-case phase voltage (the worst of the three phas-es). The total number of distinct three-phase eventsrecorded over this period was 53, encompassing twomonitors on site. The events from the two monitors aretemporally aggregated, i.e., if both monitors reportedan event in the same time window, only one point isplotted in Figure 6.

It is notable that no voltage swells or long interrup-tions occurred during this six-month period. Narrowvoltage transients, less than 30- to 50-µs duration, arenot captured by the monitors. The need for coordinat-ed surge protection is well established, and manyplants include this protection routinely. The need forsag protection is much more site dependent. Forinstance, this site, typical of many industrial locations,validates that a voltage sag correction device wouldhave provided adequate process protection.

The Web site includes options for plotting theMAG-DUR data alongside standard industry voltagesusceptibility curves, such as SEMI F47 [6] and ITI(CBEMA) [7].

Definite Grid Event DeterminationOn 4 November 2002, a single-engine aircraft struck345-kV transmission lines near Fond du Lac, Wiscon-sin. Monitors located within the same transmissionzone, as much as 50 miles distant, recorded resultingdistribution system voltage sags. Of approximately 25monitors deployed in Wisconsin at the time, fivedetected the related events as PQ events, i.e., with rmsvoltage falling below the voltage sag detection level,while other monitors recorded reduced minimum rmsvoltages in the periodic rms reports.

The system event log for Wisconsin during thisperiod is listed in Table 2. Detail from one event, ID1695, captured on a nominal 480 V three-phase line, isshown in Figure 5. In such a case of voltage sag on theEHV transmission system, all related 69-kV subtrans-mission lines will be affected as well.

Examination of event summary data from sitesacross a region can be used to identify “definite gridevents,” i.e., those PQ&R events that were definitelypropagated on the utility grid, as opposed to “inter-nal events” that are limited to a single facility. Fur-thermore, events with nearly simultaneous timestamps and known geographic proximity can be clus-tered and reported as single physical events. Thesepowerful event clustering and data aggregation capa-bilities are only possible from a monitoring systemwith a central database. Knowledge of which eventsare definite grid events greatly aids in troubleshoot-ing PQ&R problems.

Conclusions Industrial and commercial electricity consumers andthe utility companies that serve them need access toPQ&R information that is relevant and timely. Fromimproving the utility-customer relationship to trou-bleshooting facility wiring problems and selectingPQ&R mitigation equipment, better and more com-plete information are vital to process reliabilityimprovement efforts.

The PQ&R monitoring system described here pro-vides the means to gain this information by removingprevious cost barriers and moving system intelligenceto a central computing server. The approach also allowsfor a monitor evaluation period to be immediately fol-lowed by scaling to company-wide deployment.

This article has presented several case studies fromindustry applications, providing a glimpse at thepotential uses of corporate-wide PQ&R informationgathering, aggregation, and reporting. The system hasbeen independently tested by several industrial users,utilities, and EPRI-PEAC. Deployment of monitorscontinues through individual industrial and commer-cial sites, corporate and utility programs, and a cooper-ative program with the DOE.

System enhancements are under continual develop-ment and firmware upgrades can be automaticallyrolled out to all installed monitors. The system isexpected to expand to cover all of North America andseveral overseas countries.

References [1] IEEE Recommended Practice for Design of Reliable Industrial and Commer-

cial Power Systems, IEEE Standard 493, 1998. [2] D. Divan, G. Luckjiff, W. Brumsickle, J. Freeborg, and A. Bhad-

kamkar, “A grid information resource for nationwide real-timepower monitoring,” IEEE Trans. Ind. Applicat., vol. 40, pp.699–705, Mar/Apr 2004.

[3] Electrotek Concepts, Inc., “An Assessment of Distribution SystemPower Quality, Volume 2: Statistical Summary Report,” EPRI Tech.Rep. TR-106294-V2, May 1996.

[4] D.O. Koval, R.A. Bocancea, K. Yao, and M.B. Hughes, “CanadianNational Power Quality Survey: Frequency and duration of voltagesags and surges at industrial sites,” IEEE Trans. Ind. Applicat., vol.34 pp. 904–910, Sep/Oct 1998.

[5] A. Bendre, D. Divan, W. Kranz, and W. Brumsickle, “Equipmentfailures caused by power quality disturbances,” in Conf. Rec. 2004IEEE-IAS Annu. Meeting, vol. 1, pp. 482–489.

[6] Specification for Semiconductor Processing Equipment Voltage SagImmunity, Semiconductor Equipment and Materials International(SEMI) standard, SEMI F47-0200, Aug. 1999.

[7] Information Technology Industry Council (ITI), ITI (CBEMA)(revised 2000) Curve Application Note . [Online]. Available:http://www.itic.org/technical/iticurv.pdf

William E. Brumsickle ([email protected]) is withSoftSwitching Technologies in Middleton, Wisconsin. Deepak M.Divan is with Georgia Institute of Technology in Atlanta, Geor-gia. Glen A. Luckjiff is with Citadel Investment Group, LLC,in Chicago, Illinois. John W. Freeborg is with Sony PicturesDigital Networks in Madison, Wisconsin. Roger L. Hayes,Ph.D. is with Orbitz, LLC, in Chicago, Illinois. Divan is aFellow of the IEEE. Brumsickle is a Member of the IEEE. Thisarticle first appeared in its orginal form at the 2003 IEEE/IASAnnual Meeting.

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