arrester placement.pdf

1742 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 25, NO. 3, JULY 2010

A Practical Evaluation of Surge Arrester Placementfor Transmission Line Lightning Protection

Karthik Munukutla, Member, IEEE, Vijay Vittal, Fellow, IEEE, Gerald T. Heydt, Life Fellow, IEEE,Daryl Chipman, and Brian Keel, Senior Member, IEEE

Abstract—The use of metal–oxide varistor surge arresters(MOVs) in lightning protection of overhead transmission lines toimprove reliability is of great interest to electric utilities. Howeverdue to economic reasons, it is not possible to completely equip anoverhead transmission line with surge arresters at each transmis-sion structure. In this paper, an evaluation of lightning protectiondesign on a 115 kV transmission line using surge arresters,utilizing a model based on field data, is presented. The modeldeveloped is used for computer simulation using the AlternativeTransients Program. Various design procedures aimed at maxi-mizing the reliability of service on the transmission line using aminimal number of surge arresters are analyzed. Different designsconsidered for transmission line lightning protection using MOVarresters include: the use of a different number of surge arrestersper tower, distance between towers with surge arresters and thedependence of these configurations on tower footing resistance.The lightning protection designs are analyzed using ‘lightningflashover charts,’ proposed in this paper. Also, an analytical modelof two 115 kV transmission lines in Southwest U.S. has beendeveloped and different surge arrester location strategies used onthese transmission lines have been analyzed. Practical experiencesand effectiveness of various lightning protection designs used onthese transmission lines are discussed.

Index Terms—Backflashover, lightning protection, overheadtransmission lines, surge arresters, surge arrester location, trans-mission engineering.

I. LIGHTNING PROTECTION OF OVERHEAD

TRANSMISSION LINES

E XPERIENCES of various utilities have proven that theuse of line surge arresters is an efficient technique in

improvement of lightning performance of overhead transmis-sion lines [1], [2]. Surge arresters avoid lightning flashoversby maintaining the voltage across insulators on a transmissionline below the insulation withstand capability. In general,for transmission lines without shield wires, the use of surgearresters at every insulator location is an alternative for shieldwire protection [3]. For transmission lines with shield wires,line surge arresters are used at remote locations where line

Manuscript received June 01, 2009; revised November 02, 2009, December16, 2009, December 18, 2009. First published April 05, 2010; current versionpublished June 23, 2010. Paper no. TPWRD-00417-2009.

K. Munukutla is with Entergy, Jackson, MS 39205 USA (e-mail: [email protected]).

V. Vittal and G, Heydt are with the Department of Electrical, Computer,and Energy Engineering at Arizona State University, Tempe, AZ 85287 USA(e-mail: [email protected]; [email protected]).

D. Chipman and B. Keel are with the Salt River Project, Phoenix, AZ 85034USA (e-mail: Daryl.Chipman)@srpnet.com; [email protected]).

Digital Object Identifier 10.1109/TPWRD.2010.2040843

maintenance is difficult or at places of high ground resistivity(e.g., rocky terrain, sand) [4]. In contemporary transmissionengineering, line surge arresters are used on several key trans-mission lines to improve the reliability of service. Howeverdue to economical reasons, it may not be possible to equip theline with surge arresters at each transmission structure. Theserequirements motivate a study to design a strategy aimed atminimizing the number of surge arresters to achieve a desiredlightning protection.

Several studies [2], [5]–[8] have been performed to assess thelightning protection of transmission lines. However, the effec-tiveness of surge arrester installation location in transmissionline lightning protection has not yet been fully quantified. Inthis paper, the lightning performance improvement offered byvarious surge arrester location strategies and use of differentnumber of surge arresters per tower on transmission lines withshield wires is discussed.

This paper presents a non-statistical deterministic studyon the Alternative Transients Program (ATP), which is thecommonly used and the public domain version of the Elec-tromagnetic Transients Program (EMTP), to estimate theimprovement of lightning performance of transmission linesusing different surge arrester location strategies. Analyticalmodels of two transmission lines in the Southwest U.S., con-sidering the characteristics of each line section, are constructedbased on field measurements. Accurate tower-by-tower repre-sentation of transmission line components is developed basedon the modeling guidelines given in [9]–[12]. Surge arrestersare modeled using the frequency dependent equivalent circuitrecommended by an IEEE working group [13].

Arrester location strategies that can be used on the trans-mission lines were analyzed using parametric and sensitivitystudies. These studies help in identifying the strategies usefulin locating line surge arresters on transmission lines. Variousstrategies analyzed in this study are: installation of differentnumber of surge arresters per tower, distance between towerswith surge arresters. The lightning protection design strategiesare analyzed with the help of tables described in this paper as“lightning flashover charts.” These charts are a graphic repre-sentation of those components that are expected to flashover fora given lightning strike event. In effect, the lightning flashovercharts present the probability of an insulator back flashoverwhen a lightning stroke of a specified magnitude strikes atransmission tower.

This paper is organized as follows: the modeling details anddata for the study transmission lines are presented in Section II.In Section III, an illustration of a case study on a 115 kV line

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MUNUKUTLA et al.: PRACTICAL EVALUATION OF SURGE ARRESTER PLACEMENT 1743

Fig. 1. Steel lattice-type tower design and conductor arrangement (A, B, C arephase conductors and D, E are shield conductors).

section showing the effectiveness of various strategies involvingsurge arresters in transmission line lightning protection is pre-sented. Sensitivity study with respect to different modelingmethods is presented in Section IV. Analysis of results obtainedfrom studies, similar to those in Section III, performed on twoactual 115 kV lines in the Southwest U.S. and suggestionsbased on practical experience are discussed in Section V.

II. MODELING DETAILS AND DATA USED

A. Study Transmission Lines

Two transmission lines from the Southwestern U.S. arechosen as test beds for analysis. The first is denominated KRSand this is a 115 kV line largely built with steel transmissiontowers. The second is denominated FM and this too is a 115kV line largely built with wooden transmission structures.The basis for the selection of these transmission lines is thesignificant reduction in number of outages and trips causedby lightning activity in the region after the installation of linesurge arresters. Data for these transmission lines such as theconductor arrangement, line length, line parameters, towerstructure and location, tower grounding resistance, line outageand tripping data, line elevation data, lightning data in theregion was collected to analyze the line lightning performance.Figs. 1 and 2 show the conductor arrangement and details of thetransmission towers used on these lines. Table I describes theparameters corresponding to KRS 115 kV line and FM 115 kVline, respectively.

B. Modeling Guidelines

The modeling guidelines used for the analysis performed areselected from various [9]–[12]. Modeling details used for repre-senting various transmission line components are described asfollows.

• Overhead lines: Overhead lines (phase conductors andshield wires) are modeled by means of several line spansof multi-phase untransposed distributed parameter fre-quency dependent line model (this is the so-called “Jmarti

Fig. 2. Steel windmill-type tower design and conductor arrangement (A, B, Care phase conductors and D is the shield conductor).

TABLE ITRANSMISSION LINE DATA FOR LINES KRS AND FM

model”). The line terminations are modeled as longenough line sections to avoid reflections that could affectthe overvoltage at the insulator location [9].

• Steel and wooden transmission towers: Transmissiontowers are modeled by using separate sections between thecross arms. Since on all the transmission towers of woodpole construction, the shield wires are grounded througha steel wire, the equivalent surge impedance of the steelwire is used to represent its surge impedance. For steeltransmission towers, each section of a pyramidal shapedtower is approximated by an equivalent cone whose surgeimpedance is calculated from (1) and [12]

(1)

where is the height of the tower in meters, is the radiusof the base of the equivalent cone in meters. The shieldconductors are assumed to be earthed through the tower.

• Tower footing resistance: Tower footing resistance isassumed to decrease with increase in discharge currentthrough the grounding electrode. The footing resistance


TABLE IIMOV ARRESTER DATA (TAKEN FROM [15])

is therefore modeled as nonlinear current changing resis-tance given by [9], [10] shown as

(2)

where is the tower footing resistance (in ohms) atlow current and low frequency, is the lightning currentthrough the footing, and is the limiting current that caninitiate soil ionization given by [9] as

(3)

where is the soil ionization gradient which is a fixedvalue (about 300 kV/m) and is the soil resistivity inohm-m. Note that is in A in (3).

• Lightning stroke: a lightning stroke is modeled as a cur-rent source with parallel impedance equal to the lightningchannel surge impedance. The magnitude of a lightningcurrent is a probability function. This study assumes aworst case scenario (since this is a lightning protection de-sign problem) using the concave wavefront described in[10] (referred as CIGRE-type waveform in [14]) with typ-ical lightning stroke front time, s and tail time,

s (represented as a 1.2/50 s waveform). Theconcave wavefront described in [10] is called as the stan-dard lightning impulse in this paper.

• Insulator: insulators are modeled as a capacitance in par-allel to a flashover switch. The flashover switch is mod-eled based on two methods: standard withstand capabilitycurve (SWCC) and leader development method (LDM), asdescribed in [10].

• Surge arrester: a nonlinear - characteristic of surge ar-rester is modeled by a frequency dependent model sug-gested by IEEE [13]. An 84 MCOV (maximum contin-uous operating voltage) metal–oxide surge arrester is usedfor the analysis shown. The parameters used to obtain themodel are shown in Table II.

III. TEST RESULTS: THE USE OF A LIGHTING FLASHOVER

CHART FOR LIGHTNING PROTECTION EVALUATION

The approach used to analyze the effect of different surgearrester configurations on the transmission line is as follows.

1) Critical sections of KRS and FM transmission lines withprior lightning activity and with improvements in lightningprotection using surge arresters were represented in ATP

TABLE IIILFC FOR LINE A WITH NO SURGE ARRESTERS INSTALLED

(50 kA, 1.2/50 �S STANDARD LIGHTNING IMPULSE)

using the modeling procedures described in the previoussection.

2) Using ATP simulations, the critical stroke currents pro-ducing back flashover were calculated and “lightningflashover charts” (LFCs) were drawn. Lightning currentmagnitudes producing back flashover for different valuesof footing resistance are estimated.

3) The improvement in lightning protection by the use ofsurge arresters was estimated repeating the simulations dis-cussed in step 2.

4) Finally, the sensitivity of the study performed was analyzedfor different modeling procedures involved in designinginsulators.

To illustrate the analysis performed on the two transmissionlines under study, a line section comprising 11 spans of KRS115 kV transmission line (referred as line A) designed in ATPusing the data obtained from field measurements is considered.

A. Effect of Surge Arrester Location Distance

For the analysis of surge arrester location strategies, tablessimilar to Table III called ‘lightning flashover charts’ are used.Table III presents the lightning flashover chart for a 50 kA,1.2/50 s standard lightning impulse with no installed surge ar-resters on the line.

Lightning flashover chart for a specific line section depictsthe effectiveness of lightning protection design when a lightningstroke of specific intensity hits a transmission line. They aredrawn as follows: For a specific stroke location, the transmissiontower at which flashover occurs is noted; a tower at which aflashover occurs is denoted by F (unshaded box in the chart)while a tower at which no flashover is observed is denoted byN (lightly shaded box in the chart). LFCs for different lightningstroke intensities and different lightning protection designs aredrawn and compared to obtain the best possible configurationrequired for a specific lightning performance. LFCs are usedonly to offer a visual depiction of the results of the flashoverstudy and may not be of any further significance.

The effect of the surge arrester location with respect to thepoint of impact of lightning stroke on lightning protection isstudied with the help of lightning flashover charts shown in Ta-bles IV and V. Tables IV and V present the lightning flashover


TABLE IVLFC FOR LINE A WITH SURGE ARRESTERS TWO SPANS APART


TABLE VLFC FOR LINE A WITH SURGE ARRESTERS THREE SPANS APART

(50 kA, 1.2/50 �s STANDARD LIGHTNING IMPULSE)

charts when surge arresters are located on the transmissiontowers spaced two spans and three spans, respectively.

In case of a lightning stroke on a transmission tower, it is ob-served that the location of surge arresters across all the phaseinsulators of that tower prevents back flashover. Also, it is ob-served that the location of surge arresters on towers adjacent toa tower hit by a lightning stroke prevents the induced travelingwave from traveling further and therefore reduces the numberof insulators that flashover.

B. Effect of Different Number of Surge Arresters Per Tower

The effectiveness of using different number of surge arrestersper tower is studied using lightning flashover charts shown inTables VI–VIII. Table VI is a lightning flashover chart for theline A using a 50 kA, 1.2/50 s current wave with surge arrestersacross all the phase insulators while Table VII is drawn for surgearresters across two phase insulators. Table VIII is a lightningflashover chart with surge arresters across two phase insulatorsfor an 80 kA, 1.2/50 s standard lightning impulse.

The following three observations are from Tables VI–VIII:• Usage of surge arresters on all phases of transmission tower

provides protection to the transmission tower for all valuesof lightning current.

• Usage of two surge arresters per transmission tower pro-vides complete protection to a transmission tower againstlightning stroke of magnitude 50 kA. However, this methodis ineffective for a lightning stroke of magnitude 80 kA

TABLE VILFC FOR LINE A WITH SURGE ARRESTERS ON ALL PHASES


TABLE VIILFC FOR LINE A WITH SURGE ARRESTERS ON TWO PHASES


TABLE VIIILFC FOR LINE A WITH SURGE ARRESTERS ON TWO PHASES


since flashover is expected to occur on the unprotectedphase.

• LFCs are not symmetrical owing to the nonuniformity ofthe line configuration (e.g., change in footing resistances,tower surge impedances across the line).

C. Effect of Tower Footing Resistance

Fig. 3 presents the effect of tower footing resistance on light-ning stroke magnitude that produces back flashover for a defi-nite number of surge arresters per tower. It is estimated that withsurge arresters on all phases of a transmission tower, a lightningstroke of magnitude 85 kA or higher at the tower can produce a


Fig. 3. Effect of footing resistance on lightning protection designs.

TABLE IXEFFECTIVENESS OF USAGE OF DIFFERENT NUMBER

OF ARRESTERS PER TOWER FOR LINE A

Fig. 4. Plot showing the expected number of back flashovers versus spacingbetween poles with surge arresters for different configurations of surge arresterplacement (for 50 kA, 1.2/50 �s standard lightning impulse).

flashover at the adjacent tower. Table IX summarizes the min-imum lightning current handled by a transmission tower withouthaving insulator back flashover using different number of surgearresters on a tower (as shown in the plots in Fig. 3).

D. Comparison of Various Arrester Protection Designs

Figs. 4 and 5 show the plot of the expected number of flashedinsulators as a function of spacing between the poles havingsurge arresters for different lightning current magnitudes. Thesefigures present a comparison of lightning protection offered bythe two configurations: 1) surge arrester on every phase of atransmission tower and 2) surge arresters on two phases of atransmission tower.

Fig. 5. Plot showing the expected number of back flashovers versus spacingbetween poles with surge arresters for different configurations of surge arresterplacement (for 80 kA, 1.2/50 �s standard lightning impulse).

TABLE XCOMPARISON OF BACK FLASHOVER RATE FROM

THE STUDY WITH IEEE FLASH PROGRAM 1.9

Plots in Figs. 4 and 5 indicate that spacing of surge arrestersevery 1, 2, or 3 span lengths apart on a transmission linecan help in improvement of lightning protection. However,installing surge arresters on two phases of a tower can onlyhelp with partial improvement in lightning protection (which isobserved to be 50 kA lightning stroke for the line A).

IV. RESULT VALIDATION AND DESIGN SENSITIVITY STUDY

Using the actual distribution of footing resistances for thetransmission lines, the back flashover rate was computed usingthe IEEE flash program (Version 1.9, described in IEEE Stan-dard 1243 [4]). This back flashover rate was compared with anapproximate back flashover rate computed from the study re-sults using CIGRE guidelines [10]. The results for the analysisare presented in Table X for a keraunic level of 40 thunder daysper year. A slight overestimation of the back flashover rates fromthe study results is due to the usage of 1.2/50 s lightning wave-form and neglecting corona for the study.

A sensitivity study aimed at estimating the effect of differentmodeling techniques associated with insulator strings is per-formed to obtain an estimate of the accuracy of the study per-formed. The modeling techniques used for comparison are stan-dard withstand capability curve (SWCC) (defined in IEEE Std.1243 [9]) and leader development method (LDM) (defined inCIGRE guidelines [10]).

To analyze the sensitivity of modeling techniques, the min-imum current producing back flashover is estimated at everytower along the line designed for the case study (in Section III)using ATP-EMTP for different waveforms. Fig. 6 shows theanalysis for linear ramp 1.2/50 s waveform while Figs. 7


Fig. 6. Minimum lightning peak currents causing back flashover for LDM andSWCC (using 1.2/50 �s linear ramp waveform).

Fig. 7. Minimum lightning peak currents causing back flashover for LDM andSWCC (using 1.2/50 �s standard lightning impulse).

Fig. 8. Minimum lightning peak currents causing back flashover for LDM andSWCC (using 3/75 �s double exponential wave).

and 8 present the results for 1.2/50 s standard lightning im-pulse and 3/70 s nonstandard double exponential waveform,respectively.

The following conclusions can be drawn from the resultsshown in Figs. 6–8:

• The nonuniformity in the lightning currents causing back-flashover at the tower insulators is due to the changes intower footing resistances and tower surge impedances.

• The magnitude of lightning current at which insulatorbackflashover occurs at a transmission tower is depen-dent upon the type of injected current waveform. It canbe observed that minimum lightning peak causing back

flashover at the 115 kV insulators is higher for 1.2/50s standard lightning wave than for 3 s/100 s double

exponential wave.• Different insulator models perform differently for different

waveforms. In case of linear ramp waveform, both LDMand SWCC methods produce similar results; however theyproduce varied results for CIGRE-type waveforms. SWCCis a method modeled for linear ramp-type waveform whileLDM is a generalized method and is applicable to any typeof waveform.

• SWCC produces conservative estimates for lightning cur-rents and is computationally less burdensome than LDM.

V. ANALYSIS ON THE KRS AND FM LINES

A systematic analysis was performed on the KRS and FM 115kV transmission lines to determine the improvements offeredby surge arrester protection designs similar to those used in thecase study discussed in this paper. Lightning flashover chartsfor various sections of the line are used to determine the perfor-mance of the line for previously recorded lightning activity atthe vicinity of the line. The following observations were madefrom the analysis:

• Location of surge arresters in a regular span of 1, 2, or3 span lengths can result in optimal improvement in linelightning performance. These surge arrester location con-figurations not only reduce the failure rate by insulatorflashover on a tower with surge arresters but also reducethe number of flashed insulators on towers without surgearresters due to a lightning stroke.

• The probability of flashover is less for KRS line than FMline due to the use of surge arresters two span lengths apart(i.e., on every alternate pole). Such a configuration of surgearrester arrangement also helps with the reduction of theoverall outage rate due to lightning.

• Digital fault recorder (DFR) data on the lightning inducedfaults on the transmission lines suggests that most fault lo-cations are local high altitude locations (observed from theline altitude data). Therefore, it is suggested that transmis-sion towers at local peaks or high altitude locations be pro-tected with surge arresters locations which are one spanlength apart.

• The effect of lightning stroke on a transmission tower or thesurge arrester location design is independent of the trans-mission tower type used for construction.

VI. CONCLUSION

Determination of effective surge arrester locations is depen-dent on the analysis of over voltages caused by lightning strokeson overhead transmission lines with and without existing surgearresters. Accurate determination of over voltages generated duea lightning stroke necessitates the accurate equivalent represen-tation of electrical equipment such as overhead transmissionlines, tower footing resistance, insulators, and existing surge ar-resters. In this paper, systematic flashover analysis has been per-formed for a case study involving a 115 kV overhead line usingvarious possible surge arrester arrangement techniques such asusing different number of surge arresters per tower and varyingthe distance between towers with surge arresters. The effect of


factors such as footing resistance, model design accuracy on ar-rester arrangement design on a transmission line was illustrated.

The lightning flashover chart is proposed to obtain a conve-nient visual depiction of simulation results. This chart shows theeffectiveness of arresters by showing which insulators flashoverfor various lightning stroke intensities.

A similar approach was implemented in a tower by towerrepresentation of two transmission lines in the Southwest U.S.to estimate the improvements offered by the lightning protec-tion design using surge arrester. Based on practical considera-tions and study results, possible lightning designs using surgearresters were suggested.

REFERENCES

[1] A. Schei, “Application of metal oxide surge arresters to overhead lines,”Electra, no. 186, pp. 82–114, Oct. 1999.

[2] L. C. Zanetta, C. Ede, and M. Pereira, “Application studies of line ar-resters in partially shielded 138 kV transmission lines,” IEEE Trans.Power Del., vol. 18, no. 1, pp. 93–100, Jan. 2003.

[3] IEEE Guide for the Application of Metal Oxide Surge Arresters forAlternating Current Systems, IEEE Std. C62.22-1991, Jul. 1998.

[4] IEEE Guide for Improving the Lightning Protection of TransmissionLines, IEEE Std. 1243-1997, Jun. 1997.

[5] J. A. Martinez and F. Castro-Aranda, “Lightning performance of over-head transmission lines using the EMTP,” IEEE Trans. Power Del., vol.20, no. 3, pp. 2200–2210, Jul. 2005.

[6] I. M. Dudurych, T. J. Gallagher, J. Corbeit, and M. V. Escudero,“EMTP analysis of the lightning performance of a HV transmissionline,” Inst. Elect. Eng. Trans. Gen. Transm. Distrib., vol. 150, no. 4,pp. 501–506, Jul. 2003.

[7] L. Ekonomou, I. F. Gonos, I. A. Stathopoulos, and F. V. Topalis,“Lightning performance evaluation of hellenic high voltage transmis-sion lines,” Electric Power Syst. Res., vol. 78, no. 4, pp. 703–712, Apr.2008.

[8] H. Schmitt and W. Winter, “Simulation of lightning overvoltages inelectrical power systems,” presented at the Int. Conf. Power SystemTransients, Rio de Janeiro, Brazil, Jun. 24–28, 2001.

[9] IEEE Task Force on Fast Front Transients, “Modeling guidelines of fastfront transients,” IEEE Trans. Power Del., vol. 11, no. 1, pp. 493–506,Jan. 1996.

[10] CIGRE Working Group 33-01, “Guide to procedures for estimating thelightning performance of transmission lines,” CIGRE Tech. Brochure63, Oct. 1991.

[11] J. A. Martinez-Velasco and F. Castro-Aranda, “Modeling of overheadtransmission lines for lightning studies,” presented at the Int. Conf.Power System Transients, Montreal, QC, Canada, Jun. 2005, paper47-24b.

[12] M. Darveniza, M. A. Sargent, G. J. Limbourn, L. A. Choy, R. O. Cald-well, J. R. Currie, R. H. Holcombe, and R. Frowd, “Modeling for light-ning performance calculations,” IEEE Trans. Power App. Syst., vol.PAS-98, no. 6, pp. 1900–1908, Nov. 1979.

[13] IEEE Working Group 3.4.11, “Modeling of metal oxide surge arrester,”IEEE Trans. Power Del., vol. 7, no. 1, pp. 302–309, Jan. 1992.

[14] “Alternative Transient Program Rule Book,” Can/Am EMTP UserGroup, 1997.

[15] Hubble Power Systems, Protecta Lite Systems. Columbia, SC.[Online]. Available: http://www.lightshine.ae/pdf/polymer/Pro-tecta%20Arrester%20Application.pdf

Karthik Munukutla (S’07–M’09) received theB.Eng. degree in electrical engineering from Os-mania University, Hyderabad, India, in 2007 and theM.S. degree in electrical engineering from ArizonaState University, Tempe, in 2008.

Currently, he is a Planning Engineer with Entergy,Jackson, MS.

Vijay Vittal (S’78–F’97) received the B.E. degree inelectrical engineering from the B.M.S. College of En-gineering, Bangalore, India, in 1977, the M.Tech. de-gree from the Indian Institute of Technology, Kanpur,India, in 1979, and the Ph.D. degree from Iowa StateUniversity, Ames, in 1982.

Dr. Vittal is a member of the National Academyof Engineering and the Director of the PowerSystems Engineering Research Center (PSERC),and is Ira A. Fulton Chair Professor in the De-partment of Electrical Engineering at Arizona

State University, Tempe.

Gerald T. Heydt (S’62–M’64–SM’80-F’91–LF’08)is from Las Vegas, NV. He received the Ph.D. de-gree in electrical engineering from Purdue Univer-sity, West Lafayette, IN, in 1970.

His industrial experience is with the Common-wealth Edison Company, Chicago, IL, and E. G. &G., Mercury, NV.

Dr. Heydt is a member of the National Academyof Engineering. Currently, he is the Site Director ofa power engineering center program at Arizona StateUniversity, Tempe, where he is a Regents’ Professor.

Daryl Chipman received the B.Sc. degree in elec-trical engineering from Montana State University,Bozeman, in 1999.

He participated in a three-year rotating engineerprogram followed by six years specializing intransmission maintenance engineering. Currently,he is a Senior Engineer with the Salt River Project,Phoenix, AZ.

Brian Keel (M’98–SM’08) received the B.Sc. andM.Sc. degrees in electrical engineering from theUniversity of Illinois, Champaign, in 1988 and 1989,respectively.

Brian has 20 years of experience in the power in-dustry and is the Manager of Transmission SystemPlanning with the Salt River Project, Phoenix, AZ.

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