Economics of EHV High Phase Order Transmission

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					3386                   IEEE Transaction on Power Apparatus and Systems, Vol. PAS-103, No. 11, November 1984

                                            ECCNIVICS OF EHV HIGH PHASE ORDER TRANSNISSION

           J. R. Stewart, Senior merber                      E. Kallaur, Mester                     I. S. Grant, Senior               bnerber
                                                         Power Technologies, Inc.
                                                           Schenectady, New York

     Abstract - The economics of high phase order                                                   LINE OPTIMIZATION
transmission (six or twelve phase lines) are compared
to UHV three phase. The comparisons are developed from                          Many interactive variables affect the final cost
optimized line designs, based on realistic lifetime                        of a  transmission line, e.g. voltage, conductor type,
costs. Detailed structure designs were used in the                         size, bundling, structure types, heights, electrical
study, with terminal equipment costs included to de-                       loading criteria, insulators (configuration, electrical
velop a breakeven distance beyond which savings in the                     performance, length, load capability, type), air gap
HPO transmission line offset any increased substation                      clearances, foundation types, soil conditions, and lo-
costs. This breakeven distance is typically only a few                     cal labor and material costs. Optimization is the
miles, i.e. much shorter than projected UHV lines. A                       identification of the least cost combination of these
sensitivity analysis allows the general conclusion to                      variables. For these analyses, an economic optimiza-
be drawn that high phase order is econcmically competi-                    tion program, developed for other line design studies
tive with UHV. Additional advantages are that the HPO                      and including methods of calculating present worth of
structures are significantly smaller, and the ROW                          revenue required (PC'RR), was used [10,11j.
probably significantly narrower.
                                                                           Electrical Loading
                                                                                  Two levels of loading were                  considered for each
                order,, the use of more than three
       High phase
phases for power transmission, has been extensively
                                                                           candidate line:
studied in the last teh years. A number of papers and                              1)   3000 MW. The initial load was assumed to
reports [1-7] have presented technical characteristics                                  be 1339 MW with a load growth of 6.5% per
and benefits to be obtained by the use of more than                                     year, reaching 3000 MW at year 13.
three phases.   Increasdd power transfer over existing
rights of way and reduced electrical enviromnental im-                             2)   6000 MW. The initial. load was assumed to
pact are two of these benefits. However, for a tech-                                    be 2679 MW with a load growth of 6.5% per
nology to be applied, it must be economically as well                                   year, reaching 6000 MW at year 13.
as technically beneficial. Six phase has already been
shown to be an economic uprating tool for double cir-                       Economic Analysis Criteria
cuit lines [81.     In this paper, 462 kV (phase-ground)
six and twelve-phase -lines and 317 kV twelve-phase                                The PWRR analysis            is based on the                     folilowing
lines are compared for relative economics with a                            assumptions:
1200 kV three-phase design.
       The five high phase order schemes studied are:                              1)   All material and labor costs based upon
                                                                                        1982 U.S. dollars.
       Scheme 1 - Twelve-phase 462 kV, two conductor
       bundles, self-supporting (rigid) towers                                     2)   Generation fixed charge rate                  =   16%
       Scheme 2 - Six-phase, 462 kV, four conductor                                3)   Transmission fixed charge rate                    =   16%
       bundles, self-supporting (rigid) towers
                                                                                   4)   Discount rate       =   12. 5%
       Scheme 3 - Twelve-phase, 317 kV, single con-
       ductor bundles,    self-supporting   (rigid)                                5)   Demand charge               =      $250/kW            (assumes
       towers                                                                           combustion turbines)
       Scheme 5 - Same as Scheme 3,              except guyed                      6)   Energy charge       =   $20/MWH
       portal towers
                                                                                   7)   Required generation reserve               =       20 %
       Scheme 6   - Same as    Scheme 3, except guyed Y
       towers                                                                      8)   Economic life for payback of investment
                                                                                        is 30 years.
A Scheme 4 design was found to be structurally indeter-
minate and was not considered further. Electrical and                              9)   Loss factor     =   43%
mechanical design of these lines are given in a com-
panion paper [9].                                                                 10)   Loading of lines            as   given above.
                                                                                  11) Escalation rate           =       8.5% per year.
84 T&D 370-3      A paper recommended and approved
by the IEEE Transmission and Distribution Committee                         Any utility contemplating high phase order transmission
of the IEEE Power Engineering Society for presenta-                         will, of course, use its own economic parameters.
tion at the IEEE/PES 1984 Transmission and                                  However, a sensitivity analysis shown .later in this
Distribution Conference, Kansas City, Missouri,                             paper demonstrates that the general conclusions of the
April 29 - May 4, 1984.   Manuscript submitted                              work presented here are unchanged for reasonable varia-
October 28, 1983; made available for printing                               tions of economic parameters.
March 2, 1984.
                                                  0018-9510/84/1 100-3386$01 .00© 1984 IEEE

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Economic Choice of Conductor                                                                              TABLE I
                                                                                     Optim     Line   Design   Based   on   3000   MW Loading
     Variables in choosing a conductor are:                                                                                         .PWRR
                                                                            SCHEME VOLTAGE SPAN CONDUCTOR         $ x 1000/mi
     1)   Diameter                                                             1   462 kV 1800' 2167 kcmil Kiwi    1209.1
                                                                                   12-0          2 cond/phase
     2)   Conductor purchase price ($/lb.)
                                                                               2   462 kV 1800' 2167 kcmil Kiwi    1177.6
     3)   Conductor stringing and clipping                costs                    6-0           4 cond/phase
           (based upon conductor weight).                                      3   317 kV 1600' 2515 kcmil Joree   1112.9
                                                                                   12-0          1 cond/phase
     4)   Strength-to-weight ratio of conductor.
          This implicitly includes material and                                3A 317 kV 1600' 1590 kanil Lapwing 1065.8
          stranding. (A conductor with a higher                                    12-0          2 cond/phase
          strength-to-weight ratio can be strung                               5   317 kV  1600' 2515 kanil Joree   912.9
          tighter and     thus    requires   fewer                                 12-0          l cond/phase
          supporting structures per given distance
          than a conductor       with    a   lower                             6   317 kV 1600' 2515 kanil Joree    946.5
          strength-to-weight ratio.)                                               12-0          1 cond/phase
                                                                              UHV 1200 kV 1120' 1780 kanil Chukar  1914.3
     5)   Electromagnetic interference     criteria                                3-0           8 cond/phase
          (EMI).     (Conformance with local EUI
          restrictions could necessitate the use of
          a larger conductor     than  is   optimum
          economically).                                                                                  TABLE II
                                                                                     Opti= Line Design Based on 6000 MW Loading
     Ten different ACSR conductors were examined in
this study for each HPO structure [12,13]. The base                         SCHEME     VOLTAGE     SPAN    CONDUCTOR
case conductor was 2156 kanil Bluebird ACSR;     addi-                                                                               $ x 1000/mi
tional conductors range from 1431 koail Plover to                                1     462 kV 1800'        2167 kanil Kiwi
2515 kaiil Joree. 1780 kanil Chukar ACSR (eight con-                                                                                 1594.9
ductors per phase) was used for the UHV three-phase                                    12-0,               2 cond/phase
line. (The base conductor size for the high phase or-                           2      462 kV 1800'        2167 kanil Kiwi           1563.5
der alternatives and the conductor for the 1200 kV                                     6-0                 4 cand/phase
three-phase alternative are discussed in Reference
[9].) AC resistance for all conductors was taken at an                          3      317 kV 1600'        2515 kcmil Joree          2551.4
                                                                                       12-0                1 cond/phase
operating temperature of 500C.
                                                                                3A     317 kV     1600'    2515 kanil Joree          1854.3
Right-Of-Way (ROW) Requirements                                                        12-0                2 cond/phase
    .The required width of ROW is based on electrical                           5      317 kV     1600'    2515 kcmil Joree          2351.4
and mechanical system parameters (e.g. switching surge                                 12-0                1 cond/phase
level, maximum conductor blowout, EMI, line voltage,                            6      317 kV     1600'    2515 kanil Joree          2385.0
etc.). While there is a minimum required width for any                                 12-0                1 coed/phase
transmission line, it would not be correct to assume
that all utilities would use the minimum. Also, the                            UHV     1200 kV    1120'    1780 kanil Chukar         2115.1
cost of ROW varies widely for different locations and                                  3-0                 8 cond/phase
areas, making it difficult to assign a meaningful
dollar-per-acre ROW cost. For these reasons, cost dif-                                             SENSITIVITY ANALYSIS
ferences for the candidate lines studied are presented
only as a single illustration, and are not included in                           The optimum designs in Tables I and II are results
the general case. The ROW requirements of EHV high                          of an analysis where span lengths and conductor sizes
phase order lines are less than those of UHV                                are varied.   Shorter spans.require shorter structures
three-phase lines, and can result in a significant cost                     to maintain the specified midspan clearance but need
advantage.                                                                  more structures per mile. Conversely, longer spans re-
                                                                            quire fewer structures per mile but the individual
Line Optimization                                                           structures are taller and stronger to support the addi-
                                                                            tional conductor weight. Likewise, smaller conductors
     The high phase order schemes were examined                   for   a   cost less, are lighter with resulting reduced struc-
range of spans from 800 to 1800 feet.                                       tural requirements, but have greater losses.
     Tables I and II list the optimum designs for the                       Cost Components
schemes studied for 3000 MW and 6000 MW loadings
respectively, considering the electrical and mechanical                          In addition to conductor, span and       structure
design constraints (e.g. radio and audible noise, max-                      technical parameters, various component costs may vary
imum span length).                                                          from those assumed. The economic parameters used in
                                                                            this study (including material and labor costs) were
Scheme 5 is the economic choice for the              3000    MW     load    chosen to be typical, but obviously there will be con-
($912,900/mile), and Scheme 2 for the 6000 M load                           siderable variations throughout the United States. To
($1,563,500/mile). The effect of terminal equipuent                         assess the sensitivity of the PWRR to changes, a
costs on the optimum choice is given below in Tables IX                     50 percent adder was applied to the following to ex-
and X.                                                                      amine their effects on the overall MWRR:

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                1.    Conductor cost                                                         Different Conductor Bundles (Schemes 3 and 3A)
                2.    Stringing and sagging cost
                3.    Tower steel cost                                                            The analysis shown in Tables I through III is
                4.    Tower erection cost                                                    based on a single conductor per phase for Scheme 3 to
                5.    Generation demand charge                                               provide an extreme comparison of lower phase-ground
                6.    Generation demand escalation factor                                    voltage and small conductors, so losses have the maxi-
                7.    Generation energy charge                                               mum effect. Scheme 3A in Tables I and II uses the same
                8.    Generation energy escalation factor                                    self-supporting steel tower as Scheme 3 except that the
                                                                                             optimization process is conducted over a range of con-
     A summary of the sensitivity analysis appears                                      in   ductors with two conductors per phase. Double conduc-
Table III.                                                                                   tor bundles result in savings of 4 percent for 3000 MW
                                                                                             loading and 27 percent for 6000 MW over the single con-
                                 TRABLE III                                                  ductor bundle case.    The economic choice of Scheme 5
            Sensitivity of 8R, Based Upon 50 Percent Cost Gradient                           for a 3000 MW load and Scheme 2 for 6000 MW remains
                                                                                             unchanged. However, double conductor bundles do result
                                                                                             in 317 kV twelve-phase having lower cost than UHV for
                               3000 MW LINE LQADING             6000 MW LIE LOADING
                                              WEIITGE                         WEICR1'E       6000 MW, and the possibility of overall superiority
                                              $ x 100' 0/rni.
                                                                              $ x 1000/li.
                                                                                             when terminal equipment costs are considered.
    1                                                                                        Design Assumptions: Maximum Ground Level E Field
                      1         14.14           1380.1           10.72         1765.9
                      2          7.12           1294.9            5.40         1681.0
                      3          5.95           1281.6            4.51         1666.8             Other sensitivity analyses are possible by varying
                      4          8.60           1313.1            6.52         1698.9        the initial design assumptions, although these were not
                      5          2.07           1234.5            6.28         1695.1
                      6          3.62           1252.6            9.56         1766.7        included in the cost values above. Spacing and clear-
                      7          3.25           1249.0            9.25         1749.7        ance configurations of the high phase order schemes
                      8          5.68           1278.0           15.01         1854.5        were designed to permit a maximum ground level electric
        2                                                                                    field strength of 8 ky/meter [9]. If this restriction
                      1         14.52           1348.4           10.94         1734.5        were relaxed to allow a higher ground level field
                      2          7.31           1263.6            5.51         1649.6
                      3          5.32           1240.0            4.00         1626.0        strength (e.g., 11 ky/meter), the result would be
                      4          7.69           1268.3            5.79         1654.0        shorter towers with lower overall costs. For example,
                      5          2.13           1202.3            6.02         1663.5
                     -6          3.72           1221.2            9.77         1732.7        if the Scheme 1 tower height were decreased by 5 feet,
                      7          3.34           1216.5            8.77         1716.9        the tower would weigh 1250 pounds less and cost $625
                      8          5.83           1245.9           15.33         1820.5
                                                                                             less. For 1800' ruling spans, this would decrease the
                      1          9.11           1214.2            3.97         2652.7
                                                                                             line installed cost by $1833 per mile.
                     2           8.32           1205.3            3.63         2644.0
                     3           2.90
                                                1145.2            1.26         2583.5        Insulators and Foundations
                     4                          1159.6            1.83         2598.1
                     5           8.38           1206.4           14.63         2924.7
                     6          14.66           1276.5           25.59         3204.3             One set of mechanical loading criteria was used
                     7          13.16           1259.8           22.96         3137.2        for the insulator system designs for the high phase or-
                     8          23.02           1368.9           40.16         3576.0
                                                                                             der structures.   To Lnore accurately model the overall
                     1           9.11            996.0            3.97         2444.8
                                                                                             scheme costs, a series of detailed insulator designs
                     2           8.32            988.7            3.63         2436.8        should have been used. The outcome might influence the
                                                                                             actual PWRR costs, but the economic ranking of line de-
                     5           8.38            989.6           14.63         2695.4        signs is not expected to change, particularly since the
                     6          14.66
                                                1046.7           25.59         2953.1        optimized solution is very close to the base case
                     7                          1033.0           22.96         2891.3
                     8          23.02           1123.0           40.16         3295.7        design.
                                                                                                  As for the insulator loadings, the foundations
                     1           9.11           1032.7            3.97         2479.7        used in the high phase order structures were not
                     2           8.32           1025.2            3.63         2471.6
                     3           2.90            973.9            1.26         2415.1        examined for sensitivities due to loading changes.
                                                                                             Obviously, an actual line design would require detalieo
                     6          14.66           1085.3           25.59         2995.3        foundation costs as a function of loading-changes, and
                                                                               2932.6        the PWRR would change for each individual line, but the
                                                                                             economic ranking would also probably remain the same.


                                  -               _
                                                                                                             ECONOMICS OF LINE TER4INALS
                     3            -               _
                     4            -               _                                               For this analysis, it is assumed that a new
                     5           0.7            1927.3            2.5          2167.2
                     6            -                                                          voltage level is being brought into a substation.
                     7           1.1            1934.8            3.9          2196.9        Transformation will be installed for the full line
                     8            -
                                                                                             capacity to a lower voltage level presently existing in
                                                                                             the station, assumed to be 345 kV (three-phase). For a
    1       -
                Conductor Cost      2 Stringing and Sagging Cost
                                                                     3 - Toer Steel Cost     point-to-point application a terminal will be required
    4       -   Tower Erectic* Cost     5 Generaticn Denand Charge
                                                                                             at each end.
    6       -   Generation Demand Escalation Factor   7 - Generation Enrgy Charge
    8       -   Generation Energy Escalation Factor                                               The economic analysis of substations is even more
                                                                                             camplex than that of transmission lines. The variety
                                                                                             of bus arrangements, protection schemes, other lines
     From Table III, the high phase order Scheme 3                                           that may terminate at the same substation, ground mat
design is still the most economic for 3000 MW loading,                                       requirements, and utility design specifications regard-
while the 1200 kV UHV three-phase option remains the                                         ing switching and reliability, make substation costing
                                                                                             a difficult and highly variable process. However, in
most expensive. The high phase order Scheme 2 is still
the most economic for 6000 MW loading, while the high                                        contrast to transmission lines, substation costs are
phase order Scheme 3 remains the most expensive.   Thus
                                                                                             generally dominated by a few large units             of
a 50 percent increase in the individual cost components
                                                                                             equipment--transformers and circuit breakers-- and er-
leaves the ranking of options unchanged.                                                     rors in properly accounting for protective relaying and

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other smaller items have a minor impact on the overall                                                     TABLE V
cost of the station.                                                                  Transformer Cost Per Terminal ($ Millions)
Major Substation Cost Components                                                                                      LINE RATING (MVA)
     Only two major substation cost components are                            LINE   DESCRIPTION                     -3000         6000
considered in this analysis--transformers and circuit                         1200   kV 3-phase                       14.4         28.8
breaker/protective equipment.   Installed transformer
cost is generally 60 to 80 percent of total substation                         462   kV 6-phase                       15.6         27.5
cost. The costs of transformers and circuit breakers                                                                  18.8         31.3
are derived from discussions with several equipment                            462   kV 12-phase
manufacturers. Accuracy of the costs is tempered by                            317   kV 12-phase                      16.3         28.8
lack of manufacturing experience with HPO and 1200 kV
equipment. The costs of installation, engineering, and
transportation are accounted for by multipliers or ad-                     Other Terminal Costs
ders based upon the experience of several firms who
have extensive EHV substation design experience.                                 Costs associated with purchasing and installing
                                                                           the circuit breakers, protective relaying equipment,
Transformer Costs                                                           instrument transformers, surge arresters, buswork,and
                                                                           switches are determined in terms of the cost of pur-
     At EHV, transformer cost is a linear function of                      chasing circuit breakers because the circuit breaker
kVA in each voltage class and can be estimated as:                         cost dominates the non-transformer terminal costs. It
                                                                           is assumed that standard circuit breakers can be used
           transformer cost ($) = K + S x kVA                              on both the six and twelve-phase high phase order
                                                                           lines. The high phase order cost penalty then is
     where:                                                                simply due to the requirement for additional circuit
                                                                           breakers to handle the additional phases. TChree-phase
           K = base cost (in dollars)                                      SF6 circuit breakers for the 317 kV twelve-phase design
                                                                           are commercially available at a purchase price of
           S   =   rating proportionality constant (dollars/               $350,000 each. Similar breakers for the 462 kV high
           kVA)                                                            phase order tenninals are estimated to be $700,000
                                                                           each. Extrapolating these costs to the 1200 kV
                                                                           three-phase case gives a cost of approximately
                                                                           $1,200,000 each. Since UHV circuit breakers are not
     The constants in the pricing equation are a                           yet commercially available, the initial cost would
function of the transformer turns ratio, the trans-                        probably be somewhat higher due to engineering and
former efficiency, and the high voltage winding BIL.                       manufacturing development.
However, the dependence of the K and S values on these
parameters is different. From a review of the pricing                           The costs of shipping, installation, protective
policies of two major manufacturers, over a range of                       relaying, etc., are considered as a multiplier of the
three-phase unit ratings from 750 to 3000 MVA (FOA) S                      circuit breaker cost. This multiplier is taken as 3.0
is a constant equal to $3.00/kVA. The base cost of the                     [10]. The different continuous and short circuit cur-
transformer, K, depends on the MVA and the voltage                         rent levels associated with the three different line
class (specifically the BIL of the high voltage                            ratings will affect the circuit breaker cost in a
winding) as shown in Table IV.                                             secondary way, but are ignored in this study. Costs
                                                                           for this terminal equipment are given in Table VI.
                               TABLE IV
                                                                                                     TABLE VI
         Transformer Base Cost, K ($ Millions)
                                                                                           Other Terminal Equipment Costs
       (MVA)                          (kV)                                   1200    kV   3-phase installed C.B. etc. =            $3.6   million
                        317            462        693                         462    kV   6-phase               "            =     $4.2   million
                                                                              462    kV   12-phase              "            =     $8.4   million
     750-1250           1.0                1.5             2.0
                                                                              317    kV   12-phase      t=                         $4.2   million
    1500-2250           1.25               1.75            2.25
    2500-3000           1.5                2.0             2.5             Total Substation Cost Comparison
                                                                                The total installed substation cost per terminal
     The costs of transporting, installing, building a                     for 3000 and 6000 MVA capacities is the sun of the
foundation, and filling the transformer with oil are                       costs in Tables V and VI, and is given in Table VII.
accounted for by increasing the cost in Table IV by 25
percent.                                                                                           TABLE VII
Installed Transformer Costs                                                      Tbtal Installed Cost Per Terminal ($ Million)
                                                                                                           LINE RATING (MVA)
     Transformer costs are given in Table V for four
transmission line terminals-two twelve-phase (317 and                            LINE DESCRIPTICN          3000      6000
462 kV    phase-ground),      one      six-phase(462 kV                          1200 kV 3-phase           18.0      32.4
phase-ground), and one        three-phase       (1200 kV
phase-phase) -for 3000 and 6000 MVA ratings.                                      462 kV 6-phase           19.8      31.7
                                                                                  462 kV 12-phase          27.4      39.7
                                                                                  317 kV 12-phase          20.5      33.0

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Discussion of Terminal Costs                                                class, which means that new terminal equipnent is re-
                                                                            quired at both ends of the line to carry the full an-
     Table VII shows that the terminal costs for the                        ticipated line loading for each alternative. This is a
high phase order lines are generally slightly higher                        reasonable approach since the first application of UWV
(about 10%) than the terminal costs associated with the                     will probably be of this nature. One example is a high
1200 kV UHV 3-phase line.                                                   capacity connection across the Cascade Mountains where
                                                                            right of way is environmentally limited, but a high ca-
     The two major reasons for the higher                high phase         pacity link may be needed in the future. Following the
order terminal costs are:                                                   installation of the first line of a new voltage class
                                                                            or phase order, a system will develop where lines are
                                                                            interconnected, and it is no longer necessary to in-
        1)    At low MVA ratings, more      transformer                     clude full transformation at both ends of each line.
              units are assumed for the phase and volt-                     It is reasonable to use the point-to-point scenario for
              age transformation than for the voltage                       this analysis since both UHV and high phase order will
              transformation required by the 3-phase                        be first applied in this manner.       This gives full
              1200 kV line. That is, only one 3-phase                       weight to any terminal cost penalty which may be
              transformer is required to terminate a                        charged against high phase order designs and thus gives
              3000 MVA 3-phase line whereas four 750                        a conservative comparison.
              MVA 3-phase transformers are required for
              the 12-phase alternative. In both cases                            Table IX presents the breakeven distance for
              the voltage is transfonmed to 345/ 1.732                      3000 MW loading for the UHV line and high phase order
              kV to ground, but additional transformers                     Schemes 1, 2, 3, and 5 using the line PWRR from
              are required to convert the 12 phases to                      Tables I and II. A "Scheme 3A" is added to include the
              3. The cost difference is due to the                          optimum double conductor Scheme 3. This provides a
              base cost of the single 3-phase 1200 kV                       comparison of the three self supporting structures for
              versus the base cost of the four 462 kV                       different voltage/phase order combinations and the most
              or 317 kV units.     In reality, it is                        economical guyed structure.
              likely that special 3 to 6 or 3 to
              12-phase transformers will be built that                                               TABLE IX
              would somewhat reduce        this    cost                                 Breakeven Distance, 3000 MW Loading
              difference.                                                             (Cost in Millions $, Distance in Miles)
        2)    High phase order needs additional circuit                                                                 SCHEME
              breakers and associated hardware. For                                                SCHEME SCBE SCHEME      3A  SaHEME
              example, a single 3-phase circuit breaker                                               1       2     3     120     5
              is required for the 3-phase line whereas                                               120     60    120 2-burnd   120
              four 3-phase breakers are required for a                                    WHV      462 kV 462 kV 317 kV 317 kV 317 kV
              12-phase line. The cost of each of the
              four breakers is less than the cost of                        PWRR          44.8      68.2       49.2       51.0       51.0
              the single breaker because those for the                                                                                          51.0
                                                                            For 2
              12-phase line are rated for a lower                           Stations
              phase-to-ground voltage, but the total
              cost is greater.                                              Line          1.914     1.209      1.178      1.113      1.066      .9129
     Despite these differences, as shown in Table VII,                      Mile
in most cases the terminal costs for HPO are comparable
to those for UHV.                                                           Break-                    33          6          8         7          6
     Table VIII gives PWRR installed costs for the line                     Even
terminals to be integrated with the line PWRR.                              Distance

                           TABIE VIII                                            Table IX shows that all the high phase order
                                                                            schemes are more econamical than the UHV line for
              Total PWRR Per Terminal ($ millions)                          3000 M loading and lines longer than 33 miles. Since
                                                                            it is unlikely that applications would be for a dis-
                                     LINE RATING (MVA)                      tance as short as 33 miles, it is reasonable to con-
       LNE  DESCRI 3ON               3000         6000                      clude that at this loading high phase order designs
       1200 kV 3-phase               22.4             40.3                  will at least be equivalent to and may often have an
                                                                            economic advantage over the UHV three-phase option.
       462 kV 6-phase                24.6             39.4
       462 kV 12-phase               34.1             49.4                       Table X gives tne breakeven distance for the same
                                                                            lines for 6000 MW loading.
       317 kV 12-phase               25.5             41.0
                                                                                  From Table X, it can been seen that the 462 kV
                                                                             six-phase schene is always the economic choice for
                                                                             6000 MW loading, while the 462 kV twelve-phase scheme
                                                                             is less costly than UHV for distances greater than 35
Breakeven Distance                                                           miles. Since the six and twelve-phase 462 kV lines
                                                                             both have approximately the same AMRR per mile, the
     A method commonly used for comparison of HVDC with                      difference in breakeven distance is due to terminal
AC alternatives is to calculate a breakeven distance                        costs. The two conductor bundle 317 kV scheme is less
where the savings fram the DC transmission line balance                     costly than UHV for distances greater than 5 miles. It
the additional cost of the DC terminals. The same                           has greater losses than the 462 kV twelve-phase scheme
technique is useful for a comparison of high phase or-                      but lower terminal costs result in a shorter breakeven
der with three-phase UHV.     For this analysis, a new                      distance.
transmission line connecting two points of an existing
system is assumed as the first of its type/voltage

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                                                                                 The purpose of this analysis was to demonstrate
           Breakeven Distance, 6000 MW Loading                              general, rather than specific, economic relationships
         (Cost in Millions $, Distance in Miles)                            between HPO and three-phase. The sensitivity analysis
                                                                            proves the generality of the conclusions developed.
                                            SCHEME                          These general conclusions are:
                       SCHEME SCHEME SCHEME    3A SCHEME
                          1       2     3     120     5                            1)   Terminal equipment costs for HPO are
                         120     60    120 2-bund    120                                generally slightly higher than those for
               UHV     462 kV 462 kV 317 kV 317 kV 317 kV                               UHV, although in certain instances they
                                                                                        may be lower.
PWRR for 2     80.6     98.8      78.8      82.0      82.0      82.0
Stations                                                                          2)    Transmission line PWRR is generally less
Line PWRR/     2.115 1.595        1.564     2.551     1.854     2.351                   for HPO than for UHV, for the same power
mile                                                                                    capacity.

Breakeven          _     35          0         *         5          *             3)    For lines longer than a      few miles,
Distance                                                                                savings in the line offset the terminal
                                                                                        equipment costs, making HPO the economic
Notes: (detailed discussion belcw)                                                      alternative.
                                                                                  4)    HPO is an alternative to UHV, at similar
*up to 20% more expensive than UHV for typical line                                     or possibly less cost. In addition, HPO
 lengths, iqnoring RiW costs                                                            lines will be smaller than UHV, and will
                                                                                        probably require less ROW.
     The single conductor bundle 317 kV schemes are
always more costly than UHV for 6000 MW lQading.                                These qualitative conclusions are unchanged by                  the
Terminal costs are comparable          between  317 kV                     sensitivity analysis or by other variables, such                      as
twelve-phase and UHV; the difference is due to the-in-                     slight differences in structure design conditions                    [9]
creased cost of losses at the lower phase-ground volt-                     and the possibility of refinements to both HPO and                   UHV
age with only one conductor per phase.                                     designs as these technologies mature.
Example Effect of ROW Cost                                                                          ACKNOWLEDGEMENTS
     The analysis of the data in Tables IX and X does                           The work reported in this paper was sponsored by
not include right of way cost, because right of way                        the Division    of     Electric    Energy     Systems,
costs vary widely, and any attempt to introduce them on                    U. S. Department of       Energy     under    contract
other than a specific basis is open to criticism.    As                    DEAC-01-78-ET-29297, Kenneth Klein Program Manager.
an illustrative example, however, if right of way width                    Mechanical structure design was developed by SAE and
were dictated by an edge of right of way ground level                      H. Brian White.
electric field of 1.5 kV/m, the 317 kV twelve-phase
schemes would require 145 feet less width than the UHV                                                  REFERENCES
line, or 17.6 less acres per mile. At $5,000 per acre,
this is an installed cost saving of $88,000 per mile or                      1.   J. R. Stewart and D. D. Wilson, "High Phase Order
a PWRR saving of $110,000 per mile for the 317 KV                                 Transmission--A Feasibility        Analysis     Part
twelve-phase lines (Schemes 3, 3A, 5, and 6) compared                             I-Steady State Considerations," IEEE Transactions
to the UHV design.                                                                on Power Apparatus and       Systems,   Vol. PAS-97,
                                                                                  No. 6 , Nov.A/Dec., 1978, p2300
Sensitivity to Terminal Cost
                                                                             2.   J. R. Stewart and D. D. Wilson, "High Phase Order
     Table IX gives the breakeven distance for the                                Transmission--A Feasibility      Analysis    Part
462 kV six-phase scheme as 6 miles. If the PWRR of the                            II-Overvoltages and Insulation Requirements,"
UHV and high phase order terminals were both increased                            Ibid., p2308
50 percent, the breakeven distance increases 50 percent
to 9 miles. If the PWRR of only the high phase order                         3.   Switching Surge Characteristics of High Phase
terminal were increased 50 percent, the breakeven dis-                            Order Lines, U. S. Department of Energy Report
tance becomes 39 miles. If the PWRR of only the UHV                               DOE/ET/29297-1, March, 1982
terminal were increased 50 percent, the six-phase line
would be less expensive for any length. Thus, terminal                      4.    Technical and Economic Characteristics of High
cost variations do not change the general conclusions                             Phase Order Transmission, U.S. Department of
regarding the economic feasibility of EHV high phase                              Energy report DOE/ET/29297-2, 1983
                                                                            5.    EHV High Phase Order Power          Transmission,
                           CONCLUSIONS                                            U. S. Department of Energy report DOE/ET/29297-3,
     An economic optimization study was made to compare
HPO alternatives to UHV transmission.       To   ensure                     6.    I. S. Grant et    al,    "Higher   Phase    Order
realism, specific technical and economic parameters                               Transmission Line Research,," CIGRE 220-02, CIGRE
were assumed and the analysis completed as for an ac-                             Symposium on Transmission Lines        and    the
tual line design. A sensitivity analysis was used to                              Environment, Stockholm, June, 1981
assess the effect of assumptions inherent in this type

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7.     I. S. Grant and J. R. Stewart,      "High    Phase                  10.   I. S. Grant and V. J. Longo, "Ecolnomic Incentives
       Order-Ready for Application," IEEE Transactions on                        for Larger Transmission Conductors,"          IEEE
       Power Apparatus and Systems, Vol. PAS-101, No. 6,                         Transactions on Power Apparatus and Systems,
       June, 1982, p1757                                                         Vol. PAS-100, No. 9, Sept., 1981, p 4291.
8.     E. Kallaur and J. R. Stewart, "Uprating Without                     11.    R. E. Clayton, "Transmission Line Econonics and
       Reconductoring, the Potential of Six-Phase,"                              Optimization,,"   PTI Newsletter, No. 25, April,
       Canadian Comnunications and Energy Conference,                             1981.
       Montreal, Oct., 1982, IEEE 82CH1825-9 p120
                                                                           12.   Transmission Line Reference Book 345 kV and Above,
9.     I. S. Grant and J. R. Stewart,    "Mechanical and                         Electric Power Research Institute, Palo Alto,
       Electrical Charatteristics of EHV High Phase Order                        Cal., 1975.
       Overhead Transmission,," IEEE 1984 Transmission and
       Distribution Conference and Exposition, Kansas                      13.   Aluminum Electrical Conductor Handbook,        The
       City, Mo., April 29-May 4, 1984.                                          Alxuminun Association, Washington, D.C., 1982.

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