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Berkeley ENE,RES C200 - TRANSMISSION AND DISTRIBUTION

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~;;.rl~.....)JbJ(/)t!IVtffl.~._-v.CUrt/1?U''l~,.CJ.~tdglt.{iclL~Zsi,jSiel'7/S,(;LOa'!).TRANSMISSION AND DISTRIBUTION 1453.10 TRANSMISSION AND DISTRIBUTIONv ., I \,"',t \, \I \r \I ,I '." \I '.~I- - - Generation- Transmission and distribution1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 19961998Year",re3.33 Transmission and distribution (T&D) construction expenditures at U.S.r-owned utilities compared with generation. Except for the anomalous spurt inplant construction during the 1970s and early 1980s,T&Dcosts have generallyed generation. From Lovins et al, (2002), using Edison Electric Institute data.While the generation sideofelectricpowersystems usually receives themostattention, the shifttowardutility restructuring, along with theemergenceofdis-tributed generation systems, is causing renewed interest in the transmission anddistribution(T&D)sideofthe business.Figure 3.33showsthe relative capital expenditures onT&Dovertimecom-pared with generation by U.S. investor-owned utilities.Themost striking featureof the graph is the extraordinary periodofpowerplant construction that lastedfrom the earlyI970s through the mid-1980s, driven largely by huge spending for':>.nuclearpowerstations.Exceptfor thatanomalousperiod,T&Dconstruction has;:, generally cost utilitiesmorethan they havespenton generation.Inthe latterhalf;\i;:;,:of the 1990s,T&Dexpenditures were roughly double thatofgeneration, with',;, most of that being spent on the distribution portionofT&D.A\~jr)The utility gridsystemstarts with transmission lines that carry large blocksi;wl~ofpower, at voltagesrangingfrom 161 kV to 765 kV,overrelatively long, ..\ -,\.~isH{distances from central generating stations towardmajorload centers. Lower-.W}~:voltagesubtransmission lines may carry it to distribution substations locatedi\QiY.Ioser to the loads. At substations, the voltage is loweredonceagain, to typi-',N:'yaIly 4.16 to 24.94 kV andsentoutoverdistribution feeders to customers. AnIi:J~,\~xampleofasimpledistribution substation isdiagrammedin Fig. 3.34.Notice"'ii·i.'~ecombinationofswitches, circuit breakers, and fuses that protect keycom-':,:rents and which allow different segmentsofthesystemto be isolated for".intenance or duringemergencyfaults (short circuits) that mayoccurin the:Stem.; J,'146THE ELECTRIC POWER INDUSTRYTRANSMISSION AND DISTRIBUTION1473.10.1 The National Transmission GridFigure 3.34A simple distribution station. For simplication, this is drawn as aone-linediagram,which means that a single conductor on the diagram corresponds to the threelines in a three-phase system.EasternInterconnectWesternInterconnectOvercurrentFeeder Relay Discon.ne;rctDisconnect.~,.Radial.orDistribution~Feeders.~'YYJ~416kVf2494kV'-~-rm{J--<¥--f FeederVoltageoBreakers RegulatorsMain BusLightningArrestorsIDistrtbutionSubstationTransformerYS~UbstatlonA.jDisconnectL....::::,.~_n-TI.~~~Bus Breaker~I.(i'fiY'J1-=f~Overcurrent- RelayISubtransmissionSystem34.5 kV -138kVThe United States has close to 275,000 miles of transmission lines, most of whichcarry high-voltage, three-phase ac power. Investor owned utilities (IOUs) ownthree-fourths of those lines (200,000 miles), with the remaining 75,000 milesowned by federal, public, and cooperative utilities. Independent power produc-ers do not own transmission lines so their ability to wheel power to customersdepends entirely on their ability to have access to that grid. As will be describedin the regulatory section of this chapter, Federal Energy Regulatory Commission(FERC) Order 2000 is attempting to dramatically change the utility-ownershipof the gridaspart of its efforts to promote a fully competitive wholesale powermarket. Order 2000 encourages the establishment of independent regional trans-mission organizations (RTOs), which could shift transmission line ownership toa handful of separate transmission companies (TRANSCOs), or it could allowcontinued utility ownership but with control turned over to independent systemoperators (ISOs).As shown in Fig. 3.35, the transmission network in the United States is orga-nized around three major power grids: the Eastern Interconnect, the WesternInterconnect, and the Texas Interconnect. Texas is unique in that its power doesnot cross state lines so it is not subject to control by the Federal Energy Reg-ulatory Commission (FERC). Within each of these three interconnection zones,utilities buy and sell power among themselves. There are very limited inter-connections between the three major power grids. After a major blackout inthe Northeastern United States in 1965, the North American Electric Reliabil-ity Council (NERC) was formed to help coordinate bulk power policies thataffect the reliability and adequacy of service within 10 designated regions of theU.S. grid.While almost all power in the United States is transmitted over three-phase ac transmission lines, there are circumstances in which high-voltageTexas InterconnectFigure 3.35 Transmission of U.S. electric power is divided into three quite separatepower grids, which are further subdivided into 10 North American Electric ReliabilityCouncil Regions. ECAR, East Central Area Reliability Coordination Agreement; ERCOT.Electric Reliability Council of Texas; FRCC, Florida Reliability Coordinating Council;MAAC, Mid-Atlantic Area Council; MAPP, Mid-Continent Area Power Pool; MAIN,Mid-America Interconnected Network; NPCC, Northeast Power Coordinating Council;SERC, Southeastern Electric Reliability Council; SPP, Southwest Power Pool; WSCC,Western Systems Coordinating Council. (EIA 200 I).de (HYDC) lines have certain benefits. They are especially useful for inter-connecting the power grid in one part of the countrytoa grid in anotherarea since problems associated with exactly matching frequency, phase, andvoltages are eliminated in de, An example of such a system is the 600-kY, 6000-MW Pacific Intertie between the Pacific Northwest and South-ern California. Similar situations occur between countries, and indeed manyof the HYDC links around the world are used to link the grid of onecountry toanother-examplesinclude: Norway-Denmark, Finland-Sweden,Sweden-Denmark, Canada-United States, Germany-Czechoslovakia, Aus-tria-Hungary, Argentina-Brazil, France-England, and Mozambique-SouthAfrica. The control and interfacing simplicity of de makes HYDC links particu-larly well suited for connecting ac grids that operate with different frequencies,as is the case, for example, in Japan, with its 50-Hz and 60-Hz


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