power systems of the future 1

7/29/2019 Power Systems of the Future 1

1/6

M ario ll abinowitz

Power Systemsofthe Future (part11he assets and working philosophy of individual util ities willT n large measure be reflecled by the modernization of theirpower systems in the next2decades. There is apotcnli al forsinartcables that can aid in thc locatioii of a fault, and possibly (by nomeans out ofthequestion) aid in tlie detection and location ( i t in-cipient faults. This will cnable repair in lhc course of routinemaintenance rather than after they have caused expensive fail-ures. Substanlially more compacl transformers are possible if wearewilling to do the necessary KBID lo develop them. A conse-quent advantage may bc lower losses. New developments usingcombinations of additives show grcal promise i n solving thetransformer oil flow clcclrificatioii problem. We will be iihlc to

supply cusloin power for clicntcle that require and value it.Superconducting fault current limiters that not only protect thcsystem but that alsoease the burden oncircuit breakers areadeli-nite possibility. Greatly improvcd rcsloration pveparcdncss willbe widely adapted. Excavation Cor undergroundlines will reach new heights of sophisticationHyperconducting materials may greatly re-duce power losses and increase power density.Propcr precantions have bccn developed for theirmanufiictuve, a s is the case for highly toxic mate-rials in semiconductor produclion. Even if theywil l bc proven to he safe in the field, lhere arc Ic -gitimate questions of public acceptance lo whichutilities will have to be increasingly responsive.Heightened public awareness of electromagneticfield issues will also continue to be addressed.Distribution automation will receive a Cavorablepublic reaclion, and enhance power delivery.The,power system of the fiitirre should cnableutilities to:* Be more competitive wilh lhcir overall strate-

e Provide better servicce Better managc their assetsExlcnd equipment lifeImprove diagnosticsDevelop reliability-centere(~maintenance.In looking ahead atthe ncxl 2decades, we willconsider various options [hat are available, pointout the less likely, and highlight those that have

the potential of achieving major improvements.A lthough thenext 20 years is a litllc soon forclis-persed generation to have a significant impact,someof the implications of dispersed generationare considered. Thc Preview of Contents thal ac-coinpanies this article is indicative of the broad

gies

rmge of topics that will hc covered in this ;ind subsequent parlsof this article, which will appear in Iuturc issues olthc IEEEPowe r Engineering Review.IntroductionDuring the I960s, thc gcneraling capacity of the U S . elcclricpower indiislry almost doubled, growing from 175 Lo 325 GW(gigawalt= 10W).In 1974.itsloodat474GW.By 1980,ithadreached 600GW. By the end of 1993, it reached 700 GW. I t isexpected that over 210 GW ol new capacity will be requii-cd by2010, bringin Ihc U S. capacity fiir the first lime inlo the TW(lerawatt=10 W) rdngc. Only about 20percent ofthi s nccdednew clectric capacity isunder construction.Increased electricity consumption has generally fol lowcd tliegrowth of the gross domestic product, even when lotal energyconsumption remains flat. With lhcpronounced movement of

$2 ;


2/6

the industry toward deregulation, intensified competition mlretail wheeling, these increased demands need lo bc accuratelyforecast. Rcgulation with respect to rights-of-way and large cap-ital outlays fiirther adds to the need to anticipate increasedpower delivery well in advance. Since these and many other fac-tors apply to both transmission and distribution systems, astrong distinction will not be made hetween tlicni at this time,and the more general term delivery will o h i be used.Prior to the worldwidc cncrgy crisisof 1974, electrici ty con-sumption i nboth the United States and in wcslcrn Europe nearlydoubled every 10years, at an annual growlh rate of about 7per-cent. For a number of years fol lowing 1974, inany combinedfactors reduced this growlh rate to 3 pcrcent annually in theUnited States. Currently, the average growth rate in domeslicelectric demand hovcrs aroond 2percent. This relatively modcslgrowth in demand could dramatically increase should electricityconsumption grow from [he present 30percent to an expected50percentol all forms of energy consumption by the year 2030.Increased population, with a corrcsponding increase in popula-tiondensity, wil l contribute to this greater rate, due significantlyto the lower cost, versatility, convenience and safety of electricenergy. General increase in the standard of living will alsobe animportant driver in the growth in use of electrical power.Transmission and DistributionAlthough traditionally high capital costs have been accept-able for transmission l ines(>35kV), they havenot been lor dis-tribution lines (535kV) with capital costsas low as.$ I-to-2 perfool ($SO00 to $10,000/mi). Thus inany new power deliverytechnologies which are capital intensive are usually eliminatedfrom consideration as potential distribution systcms. However,with increasing demand for greater reliability, decreased powerlosses, lower operating atid maintenance costs, awareness o lpossible biological effects of electroinagnetic fields, and greaterlongevity of the lines, we should also look at emerging technol-ogies that may have application to distribution despite their ini-tial high costs.Wehave learned a lessonfrom all of the questionablc distri-bution cable that was put in service 20 to 25 years aga that ini-tially low capital costs may be misleading, sincc rcplacemenlcosts canbe quite high. For those utilities that must consider theshort term, lower initial capital cost inay dominate their pcr-spcctivc. Howcvcr, for those util ities that have the foresight andcan afford to pursue the long-term, considerations of reliability,lifetime, convenience, and the entire genre ol maintcnancc, op-erations, and installation as well as initial capital costs will dom-inate their implementation of a truly modern power deliverysystem.Since the beginning oi the utility industry, insulation hasbeen the flesh and a simple good conductor such as copper oraluminum has been the backbone of power delivery. Sodiumhas been iised successfully on a small scale,but has notreceivedwide acceptance because it burns when exposed to air. Desir-able conductor properlies includc IOWcnsily, reasonably highconductivity, low cost, and chemical stability. In simple termsasa figure of merit, it is desirable that the conductivity dividedby the dcnsily be a s largc as possiblc. This f igure can be lurtherdivided by cost for an economic comparison. In this framework,amaterial like sodium would look good if it didn't burn, sincc itis about 119 asdcnsc with aconductivity about 113that of col>-per, giving it a figureof merit 3times better than copper. Sinceair is the main diclcclric for overhead lines, tensile strength isalso an important factor in this case because there isnomechani-c

cal support lrom a solid dielectric. Hcrc conducting polymer:might look good, were it not for their chemical instability. Thirwill be discussed in a later issue.Power delivery has and will play an increasingly importan)role in the utility industry. In the first half of this century, growtkin transmission line capacity was directly proportional to the in-crease in turbogenerator and power plant sizes. Due to econo-mies of scale and increased demand, turbo-generators increasecin ratings from about 1M V A and 10kV terminal vol tage in theearly 1900s to the present 1,500M V A and 25 kV with few sub-stantial changes in technology. As the generating units ancpower plants incrcascd in s i x , so too did the capacity of thetransmission lines. Toreduce losses,a s more power was carriedby a given line, i t became dcsirablc to deliver the power at eve1higher voltages. Thus voltage ratings of traiismissioii lines in theU.S. increased from 10 to 765 kV . This required high capacitystep-up transformers to connect the genelators to the transmis-sion grid, and high capacity step-down transformers atsubtransmission and distribution stations. I n less than a century.transmission linecapahilities increased from I M V A to over1,500M VA. This levcl rcprcscnts about thc largest amountopower thatautility is willing to carry onone line hecauseof reli-abili ty coiiccrns. Thc risk of losing [his much power due to linefailure, together with other contingencies, is too great aliabilityfor most util ities.

Comparing Overheadand Underground DeliveryExcluding rights-of-way costs, the installation (and presum~ably maintenance costs also) of overhead lines has been, andprobably will continue to be, less than that of underground lines.Because power line corridors come atapremium due to the bur-densome cost of rights-ol-way, overhead lines canbcas cxpcn-siveasunderground lines in densely populated areas. However;overhead lines are not a form of higli-density power transmis-sion. Any kind ol high-density power transmission, especiallyunderground l ines, requires expensive cooling. A n overheadline is effectively cooled by the large air space surrounding it,which is required for dielectric strength, and to keep the electricfield within code at ground level. However, despite the lowelcost of mostoverhead lines, it is likely that a decreasing propor-tion of power will be transmitted overhead because o lccologi-cal, practical, and aesthctic coiniderations which arc reflected intlic difficulty of obtaining new rights-of-way. So,except for tip-grading existing overhead lines, much of the new delivery ca-pacity in the future will bc underground, possibly sharing thesame corridors with overhead lines.Due i n part to their simplicity, lower cost, and caseor repair,overhead lines have been the dominant forin of delivery fromtlic carli csl days to llic present. Ncvcrlhelcss, underground lineshave seen increasing application in inany areas of the UnitedStatcs due to their greater rcliahility. However, such reliabilitycomes at substantially greater installed cost per mile. Thoughfaults may occur inore frcquently on overhead lines, they arcmore easily detected, located, and repaired. I t may be dif fi cult tomake a meaningful coinparison of fault frequency, fault dura-tion, cost of fault repair, and operating costsbetween overheadand underground delivery because the comparison needs to besite specific. Even it' we normalize with respect to aults/mile,laiilts1MVA-mile, or repair coststmile, i t may turn out to be likecomparing apples and oranges because of differences in terrainand weather.

IREE Power R?t@nrerir@Reuieui,Jat~unry o00


3/6

Overhead faults last from seconds todays depending on the cause, with the lon-ger duration caused by extremes ofweather such a s heavy ice loading, torna-docs, etc. Overhead outage rates for 138kV and lower voltage lines arc about4to6per 100miles per ycar. Thc design targctfor higher voltage ovcrhcad lines is not toexceed one outage per 100miles per yearfor lightning, and one outage pcr 1,000switching operations for switchingovervoltage operations. In both cases, anoutage is a brcakcr operation, not totalline disconnect. There is a paucity of in-formation available on outage rates, dura-tion, and costs in the open literature Corboth overhead and underground. T hereappears to he no publicly available reli-able source of this data for either trans-mission or distribution, except that keptby individual utilities and providedthrough their good auspices.According to Tom Rodenhaugh olEPRI, overhead faults probably occur ap-proximately 100 times more often thanunderground. This is usually due to windloading, lightning strikes, and tracking ondirty insulators. Salt spray also is amajorcause of faults along the coastline. M ostoverhead line faults last only a second ortwo. Most arc iutcrccptcd by h i l t limitersand relays, and easily cleared. Under-ground transmission circuits have a filultabout once per I000 miles per year. Thiswould be for 138 kV and above, whereas46, 69, and I15 kV have more faults be-cause they are either directly buried, orare placed in common duct banks withlower voltage distribution cables. Theirfrequency ol faults is roughly double atabout one per 500 miles per year. A s acomparison, distribution cablcs fail aboutonce per 100miles per year.Rodenbaugh observes that under-ground faults have a much longer averagerepair time of about a week: aiid that thecost associated with repair of an under-ground circuit can be much greater thanfor an overhead line. This is due to loca-tion difficulties, excavation if needed, aiidthe fact that most splicing can only bedone by spccializcd rcpair crcws, whomay not be immediately available. He es-timates that a single phase fault in apipe-typc transmission circuit would cmt$15,000 to $50,000depending on the se-verity.Pros and Cons ofUndergroundDeliveryAlthough convcntional self-cooled orforce-cooled undcrground high-densitypower delivery does not always have theIEEE Power En&xwin,q Keoiew,.lanemy2000

Power Systems of the FutureTable of Contents* Introduction

Transmission am1 DistributionComparing Overhead and Underground DeliveryPros aiid Cons ol Underground Delivery* Superconducting Transmission* Cryoresistive Delivery:Conventional cryorcsistivcHyperconductivityMetalized fibersJust the plain FA CT SFA CT S operating systemCustom powerImprovcd capacitorsElectrical Insulation

0 Distribution Cables:Extruded cablesImproved polymeric insulationUnderground vault explosionsAttacking the undcrgr~undexplosion problemFault locationSmart cablesNeutral and ground corrosion and protection

0 Transformers:ConventionalCoinpactFerroresonanceSolid Statc Transformer* Current L imiters:GeneralSuperconductingEmission Limited

* FACTS:

Restoration Preparedness* Compressed-Gas-I nsulated Deliverya Evaporative Cooling Delivery* Advanced Delivery Technologies Requiring Big Breakthroughs:Conducting polymersElectron-beam deliveryM icrowave deliveryLascr-beam delivery* Direct Current, Grid Stability, and Superconducting Generators* Energy Storage, Voltage Sags, and Grid Stabil ity* Power System Planning and Operations0 Biological Effects of Electromagnetic Fieldsa Dispersed Generation* Information Superhighway Synergy* Distribution Automation* Conclusi~in

7


4/6

ccological and aesthetic drawbacks of overhcad transmission, itcan have other disadvantages. I1 s expensivetomanufacture, in-stall , and operate; and its high capital and lrenching cosls resultmainly from the technical complexily ofhigh-vol lage nsulationtechnology and its associated cooling requirements. (Leakageofcooling oil caii beaserious ecological problem.) T he high opcr-stingcosts result from rclalively high charging currents associ-ated with the high voltage and high capacilance characteristicsol'underground lines; and cooling (refrigeration) ineff iciency nthe case ol' forced-cooled lines. Excavation of large trenches,special accessory equipment, and the introduction of high-ther-mal-conductivity materials to prevent thermal runaway oftenmake the installation cos1ol' underground transmission as highas the cost of the cable alone. The signil icantly lower powerdcnsity of underground distribution cahlc greatly reduces the in-stallation costs relative to transmission cable.As available corridors become saturated and power dissipa-tion increases as fast or faster than the increase in capacity, moreattention will need to he given to the lhcrinal conductivity of thebackfill. Presently,aweak concrclc slurry mix somewhat allevi-ates this prohlem. A special universal light-wcight hygroscopicbackfil l, that can easily bc shipped anywhere, is worth pursuing.EPRI helped to dcvclop a slack wax that can stabilize the thcr-mal couductivily of soil. During dry hot periods, the moisturebetween backfill parlicles evaporates away, eaving air gaps thalresult in a high thermal resistivity. T hc wax fil ls in lhcse pores,providing a thermal bridge between grains. Slack wax isan in-expensive hyproducl of oil rcfining that is stable in the ground,and is readily available in all parts cif the U.S. It can bc added tobackfill in emiilsiricd form, or by heating.Because an underground linc incurs more kinds of lossesthan an overhead linc and their impact is grealer, it may requireas much asfi ve times the cross-sectional area dconductor a s anoverhead linc to carry the same power. T hus by an inverse con-volution oi'cause and cf kct, many underground lines have totallosses lower than overhead lincs. A typical loss factor of an acoverhead line is 4.4 percent per 100milcs at345kV . Coinpasa-ble ac underground lines have losses (if about 3.5 perccnt perIO0milcs. However at500kV, the ac overheadlossesare downto 2.5 percent per 100miles. Thc losses for400 kV dc ovcrhcadare lower than 1 percent per 100milcs.Superconducting TransmissionSincea good condnctor is a key cleiiient of power delivery,le1us look at thehestconductors known, superconductors.Untillate 1986, superconductivity win considereda very low temper-aturcphenoinenon near absolutezero(0K = 273.2" C=-459.7'F).Thc accepted highest transition lemperature, T c (lempera-tiire at which a inaterial becomes a superconductor, also calledthe crilical temperature) was found Cor NbnCe at 23.2 K in 1973,where it stayed for nearly 13years. T hcrc were many reports ofhigher temperature superconductivity from I973 to 1986,butthese l'indings could iiot be replicated. Thus Tc only increasedby I9 K , from 4.2 K i n 191 , in 75 years. T his suggests a pro-jected increase of aboul 25 K per cenlury. From a inislcadiuglinear extrapolation, onc might have expccled the present, easilyrcproducedTc=125 K for TlCaHaCuO to be achieved in aboutanothcr four centuries. Insiead, to the scicntil ic world's amaze-menl, a gain of aboul 70 K occurred in a matter of months he-tween late 1986and early 1987. Such revolutions, though theydo not occur frequently, do occur regularly in science.Superconductors only have infinile conductivity Cor dc be-low a critical current density, .IC,at which point resistivity sets

in. High temperature superconductors generally are very poorconductors in the normal state, and have poor thermal conduc-livity i nboth states.For ac, there is apower loss in superconduc-tors for all values of current density. In a coaxial transmissionline, with the conduclor exposed to only itsrclativelyma l l tan-gential self-magnetic field, the power loss can be iicceptablysmall . Intercstingly, thishysteretic power loss is inversely pro-portions! to Jc. So Cor both dc and ac, it is important to have ashigh a valueoC Jcas possible. However, not21s much progress inbulk superconductors has been achieved with critical currentdensity, .IC, a s with Tc.What is iiot well known is that supercon-dnctors are ralher poor conductors in the normal state, whichculty of incorporating them into high power ap-plications.L etusexplore whether thc near-term statusof superconduct-ing technology is relevanl to the power delivery needs of theelcclric utility industry. Low-tempcrawre superconducting lines(L TSL ) have already proven to he technically fcasible. L TSL 'seconomic viahility, however, remains in doubt. For alarge sur-face-lo-volume application likea delivery line, refrigeration ef-fi ciency is crucial . T he approximately 700 Watts ofrccrigeration per watt of power dissipated (700W/W) needed forL TSL at abool4 K operation tends to make il economically nn-competitive. Thc higher the Tc ol the superconductor, thehigher the operating temperature of the cable, with obvious re-ductions in refrigeration costs. A Cringe benefil oC higher tem-perature operation is that the heat capacity of both snper-conductor and cryogen scales approximately as the cubc of theabsolnte temperature. Thus with new materials, higli-tempera-tore superconducting lines (HTSL ) operating around 77 K withonly about 1O W N of needed refrigeration inay offer an attrac-tive alternative to conventional underground delivery.Bi , , ~P ~" . ~ S L . ~ C ~ ~C U ~O I Ond its variations (commouly re-ferred to asBSCCO)with B Tc of about IO7K are being consid-ered HTSL . Because of the low thermal conductivi ty and lownorinal state electrical conductivity of HTSC, superconductingfi laments are embedded in a silver matrix (sheath) where thereisabout 4 times as much silver as superconductor by volume. Forutilities, power dclivery applicalions may have the least numberof technical obstacles lo overcome in ulilizing HTSC. (AI-though superconducting lines are inherently high current andlow vollagc, they have nolcustomarily been considered Cor dis-trihutioii because or their intrinsically high capital cost.) Never-theless, technical problems remain formidable, and even apromising delivery application may not become acommercialreality within the next 20years.For a new matcrial to be suitable for an ac HTSL , key issuesthat need to be addressed are brittlencss, ac power loss,and criti-cal current density Jc.So far, all the high temperature supercon-ductors are quite brittle. Even if a sufficiently high J c (> IO 5A/cmZ overall) can he attained in cable rorm, the power lossesinay still he cxccssively high for non-coaxial designs being pur-sued for retrofit applications. (Bear in mind that for low leinper-attire superconductors, IC> I O6 A h ? in cable form, and thedesigns were coaxial.) Power losses are exacerbatedif the mag-netic Cied seen by thc conductor is not tangential. In a coaxialdesign, the only magnetic field that aconductor sees is its a7,i-muthal self-field which is tangential to the conductor. Thus for acoaxial cable, the power dissipation Cor the threc phases is justthree times that of one phase. because there is no coupling be-tween thc phases.In a noncoaxial design, becausc of normal components ofmagnetic field and coupling between the phases, the power dis-

8


5/6

sipation for the three phases is inucli morethan lhree times thalof one phase. Superconducting filaments in ahelical tape struc-ture add to the losses. Even if the design wcre coaxial, Ihe fila-mcnts would produce normal (perpendicular) cornpoiients ofmagnetic field on each other aswell as largeeddy current lossesin thc normal silver matrix. Thisisbecause the filaments do notshield the silver from the field as would a superconducting?apewhere the superconductor shields the normal conductor. T he he-lical conductor geometry produces greater losses than would amonolithic cylinder. The presence of many filaments (ratherthan just one) hasa sinal1advantageaswell as i large disadvan-tage associated with it. The advantageis that if oneor more fi la-ments break, the currenl can be shunted throughashortdistanceof the normal silver to the other broken end, andlor other fila-ments. However, this bridging fnnction is oulweighed by con-siderably higher eddy current losses. When there are two ormore fi laments, the induced eddy current is much higher as thecurrent goes up one li lament and down the other, bridgingacross through thc silver. The eddy current loss would be muchsmallcr in the silver wilhout the many superconducting lila-mcnts, as the current would then be resistance limited. Theinii ltif ilainentary design isgood for dc magnets, hut not for ac.Becauseof this far-from-optimal design, the original hope thatpower loss for a superconducting cable will be lcss than for anormal cable wil l be d cult Lo achieve, especially while at-tempting Locarry signif icantly more power than anormalcable.Despite the formidable handicaps for the superconductingnoncoaxial design that is somewhat like a three-in-oneoil-fi lled pipe-type cable, it does haveadielectric advantage.The insulation can be at ambient temperature, T his simplifiesthe terminations (potheads), and makes it easicr to makesplices. However, the disadvantage of much grcater powerlossesinay well outweigh this advantage, and limit the applica-tions of this design to retrofitting the insides of existingpipe-type cables. Pulling the three fragile superconductingphases throughthetight space ofthc cxisting pipe will bc adif-ficult matter, particularly around bends.Subslanlial R& D expenditures on large prototypeshavebccnjustified with the argument that this isncccssary to determinecompatibility with existing syslcins. This isccrtainly necessarywhen the technology is proven. However, it inay be prematureto do so when it is not cvcn clear that the power losses will belcss than for conventional systems.If reduction in losses wcrc tlie only consideration, this couldbe done with conventional lines by going to higher vol lagcs (thetraditional approach), increasing the amount ol conductor in agiven line, or increasing the number of lines. However, powerdensity, reliabil ity, and capital cost arc foremost considerations.Thus in spite of its greater complexity, a superconducting lineneeds to be equally reliable, be no inorc expensive than its con-ventional counterparts at the same power rating, have higherpower density, and hopefully have lower power loss.For prcs-ent niiiterkals and designs, a superconducting line will likelyhave higher power density, hut may not have lower losses thanthe much cheapcr and simpler cryorcsislive cable which will bediscussed ncxl.Cryoresistive DeliveryConventional CtyoresistiveEleclrical conductivity is proportional to the electron incanfree path in a conductor, which increases as the lattice vibni-tional (phonon) scattering of the electrons decreases with dc-crcasinglemperature. In going from 300 K to about 77 K, the

electron mean free path (and hence the conductivity) iiicrcasesby apprnximatcly i i factor of 10for almost all materials, fairl yindepcndcnt of impurities and othcr lallicc defects becausephonon scattering cloniinatcs for them. (There is one exception,and that exccplioiial increase in conductivity will he discusscdin the next section.) L iquid nitrogcn (LNI ), which boils at77Kat atmospheric pressure, is tlie coolantof choice for both HTSLand cryoresistive delivery.The increase in conductivity by a lactor of 10permits a ten-fold increase in power carricd, but not without increase in powerloss. In addition to resislivc and dielectric power losses, therearealsoheat leak losses associated with thc cryogen. The rcason

for thc increased overall power loss (despite thc increased con-ductivity) relates to power loss in the refrigeration system,which requires about IOW of refrigerator powcr for every wattdissipated at 77 K.All cryoresistiveprojects Lodate have been ac at liquid nitro-gen temperature, The ininst activc work has been in J apan. In theUnitcd States, the General Elcctric Company and UndcrgronndPower Corp. have worked in this arca, but thcse projects havebeen abandoned due to technical and economic barriers.A simi-lar fate seems to have bclallcn such projects worldwide. A lum-num (AI) was the conductor of choice, although copper (Cu)wasalsoconsidered.Bothwould givean increase in conductiv-ity of only a fistor - 10a117 K . 1.et.s takea look ;II IWO novelsystems that could do much hcttcr than this, bot that were no1considered when the cryoresistive research was heing done.I iypercondnctivityOneclementstands outa s having the highest gain i n conduc-tivity, by a wide margin, coinpared toall the res1whcn cooled loLN2temperature, This is beryll ium (Be),which has R conducliv-ity at room temperature that is comparable to AI , hut which in-crcascs its conduclivily by a factor of-IO0 at 77K. Soat77K,Bc has aboul I O limes the conduclivily or AI or Cu. This wasiiotcd by Rabinowilz for cryogenic powcr iipplicalions in I977I 1 1. 1111990,Mueller el a1argued that hcrylliuin should bccoli-sidered for mine conduction applications [at 77 K], despite itswell known toxicity problems 121. They poinl 0111that Be isonly hiizardous in the form of fine airborne particulates, rcquir-ing careful control during thc inanufiicturing process, but thatBe would be rclalively safe asa finishcdproducl inelectrical q -plicalions.The low density of Be of I .8g111/cm3 s mother property thatmakes it outstandin 1 forcondnctors. This is lcss llian the densityginkm ). I t I S ICSShan lwice the dcnsily of sodiuin (0.97gm/cin), and docs not burn in air. Hcrylliuins conductivityeven at room temperature isalinosttwice thatof sodium. There-fore at 77 K,Besconductivitylgm issosuperinr tu other metal-lic conductors lhat i t shonld bc considered carefully lorcryorcsislive delivery aiid other cryogenic applications, bearingi n mind its toxicity and expense. The toxicily is possibly only aproblem i n fahrication, where carcfiil control in compliancewith some of the ciirlicsl cnvironmental laws secins to haveovercome this problem. T he cmt of Be may well go down if asufficiently large market dcvelops. A serious look at the potcn-tial of hyperconducling Be has not ycl been taken.Metul-PlatedGruphiteFibersIn going from300K lo below 4.2K (Ihe boiling poiiil of liq-uid helium st 1 atmiisphcrc), the conduclivily of most metals

of AI $2.7 g!n/cm,), y d 5 ,times lcss than that of Cu (8.9

(co,rtinued U11 page 16 )


6/6

tial amount of income redistribution through crowsubsidization.Reliability will increasingly bc sccn not merely an engincering is-sue, but also as an economic and social policy issue.T o attempt to determine who might be legally responsiblc forreliability under the new market structure, I have posed thequestion: Who do1sue if the lights go ont?The answer to thisis still rather speculative. Neverthcless, the courts might wellhold suppliers of electricity legally responsible for reliabilitythat is cither unreasonably low (and, therefore, imposes unduecosts on customers) or unreasonably high (and, thcrcfure, alsoimposes unduc costs on customers).About thePanelist

has also provided legal ad-vice to energy clients i nAlberta, as well as the Al -berta Department of Energy.He has appeared before theNational Energy Board, theOntario Energy Board, andnumerous other boards, andall levels of court, includingthe Supreme Court of Can-ada. He is the author of morethan 80 published articlesand a book, Ef f ecti ve Aduo-Andrew Roman has beenamember of the Ontario Bar for 25years and is a partner with Miller Thomson, Toronto, in its En-ergy Group. His clectricity practice includes legal work forIPPs, utili ties, and regulatory agcncies. For example, he hasbeen a legal consultant to the M acdonald Committcc, the On-lario Ministry of Energy in preparing i ts white paper on elcctric-

cacy Before AdministrutiveTribunuls. He has been asessional lecturer at four law schools,and, in spring 1998, held the chair of Natural Resources L aw atthe University oCCalgary, where he taught an advanced seminaron energy law.ity restructuring, and counsel to the Ontario Energy Board. He +

Power Systemsof the Future (continuedfrompage 9)can increase by as much as a Cactor of 100to 10,000, dependingon purity and degree of lattice perfcction. An increase in con-ductivity by a factor of 1,000 or more could result in a corre-sponding increase in deliverable powcr for dc transmission.This increase would not be as readily achieved in the ac case, be-cause the skin depth is inversely proportional to the square rootof the conductivity. Thus, thc clfective gain increases only asthc square root of the resistivity ratio, unless very thin trans-posed wires are used. A nother problem is that the degree of lat-tice perfection required to yield a large gain in low-temperatureconductivity results in a material that has extremely low tensileand shear strength. In addition to the greater expenseof makingit, thcrc would be the additional expensc oC mechanical rein-forcement. Y et the very large gains in conductivity may warrantlow tcmperature operation in certain circumstances.High purity AI is rcadily available. AI and other high puritymetals such as Cu have a very high increase i n conductivity of afactor of 10,000 at

power systems of the future 1

Documents