four – phase ac connections

8/12/2019 Four Phase AC Connections

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Four Phase AC Connections: An Alternative

Posibility for the Expansion of Transmission Grids

Goivanni Mazzanti, Member, IEEE, and Stefano QuaiaAbstract This paper investigates the economical feasibilit of four!phase "#$% overhead

transmission lines, considered as a possible alternative to the traditional three!phase "&$%

connections' The paper performs an economical comparison bet(een innovative #$

transmission lines and traditional &$ lines, (ith the goal of evaluating the contests (here a #$

connection could become convenient, accounting for different reliabilit, land occupation,

visual impact, energ losses and investment costs'

Inde) Terms *our!phase A+ transmission, po(er transmission, transmission ines'

EE+T-I+A po(er transmission is becoming a ver critical issue in man developed

countries, due to the increase in the demand of electrical po(er and to the raising concerns

about the environmental impact of high voltage lines'

This is particularl true in Europe, (here several countries are facing the opportunities and the

problems involved (ith the liberalization of the electricit mar.et, and (here e)pansion and

reinforcement of e)isting transmission sstems are increasingl re/uired, regarding both

national po(er sstems and interconnection lin.s bet(een neighboring countries'

E)pansion of national transmission grids is strongl opposed b people concerned (ith

environmental impact problems li.e the e)posure to electromagnetic fields and the visual

impact' This translates into big authorization problems and, in the last decades the e)pansionand reinforcement of transmission sstems in man countries has been slo(er than re/uired'

The need for ne( interconnection lin.s comes from the emerging progressive unbalance in

generation capabilities of different European countries "e'g', *rance, the number!one e)porting

countr, and Ital, the number!one importing countr%' E)pansion of European interconnection

(ould also improve the sstem securit, reducing the probabilit of large instabilit phenomena

li.e the blac.outs in Ital "September 011&% and in Mid!Europe "2ovember 0113%'

In this frame(or., transmission privatization could be a chance for the e)pansion of the

transmission grid' This concept has been officiall introduced in Europe b the directive 43540,

(here the term 6merchant lines7 "or 6direct lines7% is used to indicate non!institutionalinterconnections, complementar to the interconnected grid, that can be built and o(ned b

privates or po(er sstem operators' According to the subse/uent European regulation 800951&,

the merchant lines can be partl 6reserved7 or, in other (ords, their o(ners can be attractive for

large industrial customers, that can avoid the pa!tolls due to public transmission grids b

directl connecting private!o(ned production plants to their load centres'


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Ital, importing nearl 01: of the electrical energ consumed, is ver interested in the

development of interconnections (ith the neighbouring countries, as tens of pro;ects for ne(

merchant connections clearl demonstrate


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accessories' This ma.es the comparison more feasible and consistent, also because these

components are of (idespread use in European transmission sstems' An analsis similar to

that performed for the first comparison leads to the follo(ing resultsD the #$ has lo(er phase!

to!phase voltage and transfers the same po(er (ith considerabl lo(er po(er losses and current

"so that the #$ has about &&: higher load capabilit at thermal rating%' The t(o lines have

ver similar surge impedance, their phase!(ires sta on e/ual circles # &" %P Pr r= and the #$

has almost &1: higher SI and &&: higher stead!state stabilit limit MP ' The t(o considered

comparisons "among the several possible% bet(een &$ and #$ are summarized in Table I'

Some authors stated that #$ transmission can be attractive for high!capacit, long and high!

reliabilit lin.s, not onl for ?F applications but also for voltage levels close to the tpical

&91 .F used in Europe


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Investment Costs I!"#

>n the basis of a private communication from TE-2A, the transmission sstem operator "TS>%

in Ital, the p'u'l' "per unit length% investment cost can be assumed, on the average, K 1'0#

M 5.m for a #11 .F K 1'#1 M 5.m for a #11 .F 0 C &$ "these mean values include all

cost itemsD components, installation, right!of!(a, damage, notarial and various technicale)penses%'

The corresponding p'u'l' investment cost far a #$ has been evaluated around 1'&1 M 5.m


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ground circuit of the electrical stations at the t(o ends of the line and on the shield!(ire

connecting the line to(ers is provided' Secondl, for 0 C &$s the po(er transmissible (ith

three phases can be the (hole pre!fault po(er or at least a high percentage of it, depending on

the pre!fault load of the line, the conductor thermal limit, the allo(ed temporar overload and

the duration to the operation (ith reduced phases' *or #$s, even if the conductor thermal limit

is high enough to allo( temporar transmission of the (hole pre!fault po(er, the more limitedoverload capabilit of &$5#$ transformers can ma.e #$s less reliable than 0 C &$s'

Such costs result from the loss of value of the land crossed b a po(er line, o(ing to the

prohibition of building for permanent uses "houses, schools, offices, and so on% (ithin its right!

of!(a' According to


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$ractical e)amples are long lin.s bet(een po(er plants and the transmission grid, so as long

interconnection lin.s bet(een neighbouring countries'

-egarding double circuit lines, on the contrar, the possible convenience of 0 C #$s appears

e)tremel limited'

&eferences

8' S' *ontanot and S' Quaia , 62e( perspectives for po(er transmission in the European open

electricit mar.et7,Electrotech. e!." vol' @&, no' 8, pp' 3# @1, 0113'

0' T'' onders, -'N' -icheda, E' Orizaus.as, N'-' Ste(art and -'A' Bro(n, P?igh phase ordereconomicsD +onstructing a ne( transmission lineP,IEEE Tran#. on Power Del., vol' 8&, no'

#, pp' 808!803, 8449'

&' G' Samorodov, P*our!phase transmission sstems and estimation of effectiveness of their

application for po(er transmission from the three gorges plant to East +hinaP, inPro. Int.Con$. on Power S%#t. Technol." P&WEC&N'()" 8449, vol' 8, pp' 8#3 81'

#' G' Samorodov, T' Orasilni.ova, F' i.o, S' ilberman and -' Iatsen.o, P2on!conventional reliable A+ transmission sstems for po(er deliver at long and ver longdistanceP, in Proc. IEEE*Power Eng Soc. T+D Con$. and E,h--t-on" Asia $acific, 0110,

vol' 0, pp' 490!49@'

' G'R' iu and R'?' Rang, PStud of four!phase po(er transmission sstemsP, Proc. In#t.Elect. Eng. Generation, Transmission and istribution, vol' 8#4, no' #, pp' &4@!#18, 0110'

3' ' Guange and R' Rang, PThree!phase!to!four!phase transformer for four phase po(er!

transmission sstemsP,IEEE Tran#. on Power Del."vol' 8@, no' #, pp' 8189!8100, 0110'

four – phase ac connections

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