guidelines for increased utilization of existing overhead...

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Guidelines for Increased Utilization of Existing Overhead

Transmission Lines

Electra - August 2008

WG 13 Management of Existing Overhead Lines

Keith Lindsey


what are we going to talk about

• background• aim of technical brochure• technical brochure structure• economic considerations• constraints• OHL increased utilisation options• case studies• conclusions


• age of OHL about 50 years• design life 40 to 50 years has been reached• OHL matured beyond the serviceability and or economic life • OHL require some form of life extension• need to increase capacity of existing OHL • difficulties in obtaining approvals for construction of new OHL• emerging opportunities for third party utilisation (eg telecommunication)

background – why


aim of technical brochure

• guidelines for the economic & technical considerations

• transmission line asset renewal & any combination of - uprating- upgrading- refurbishment- asset expansion- life extension

• over 50 case studies are provided

• audience - executives & asset managers


given the task of carrying out a project to increase utilisation

asset managers and executives are interested in

double circuit 110 kV converted to single circuit 275 kV structure


technical brochure structure

general technical and economic considerations

expansionrefurbishment orlife extension

upgradinguprating

asset management

decision


• OHL fails to perform within the normal operating requirements without abnormal maintenance OR

• OHL is no longer fit for the original purpose

asset life definitions – technical end of life


economic model of a transmission line – whole of asset life

capital cost of OHL


time

time from nowcum

ulat

ive

NP

V c

osts

asset life definitions – economic end of life

cumulative NPV of future annual cost of the line including losses, maintenance, depreciation & risk costs per year of service is a minimum


optimum time for renewal

maximum savings in renewal costs

asset renewal economic optimisation

average long run marginal costs of

asset renewal project

asset renewal project ΣNPV with a designated financial and/or technical planning horizon


• financial constraints (budget or revenue)• labor resource constraints (internal or external)• outage constraints• technical constraints• timing constraints (approvals and public consultation)• sequential dependence on other network projects

constraints


uprating – increasing capacity

net result - risk increased

driver action propositionthermal rating by installing larger conductors

additional conductorsactive line rating systems

increasing conductor tensionconductor attachment height

adopting probabilistic ratingsredesign high surge impendance performance

voltage rating by increasing insulation strengthconductor attachment height


upgrading – improving reliability

net result - risk decreased

driver action propositionstructural performance by increasing structure strength

foundation strength

electrical performance by improving insulation pollution performancelightning performance by improving insulationlightning performance by improving earthinglightning performance by installing earthwires

reducing structure potential riseelectrical induction

installing surge diverters


refurbishment – restoring to design working life

net result - risk decreased

driver action propositionarrest degradation by restoring structure strength

foundation strengthconductor strength and capacityinsulation pollution performancefitting strengthlightning performanceinsulation pollution performance


asset expansion

net result - risk varies

driver action propositionimprove availability by increasing maintainability by adopting live line designproviding third party access by installing telco equipment


case studies – uprating thermal capacity

increasing capacity of 345kV line from 1251 MVA to 1972 MVA while energized

• replacement existing ACSR with ACSS/TW

• 52 km, 234 H frame structures• existing structures used• temporary wood poles used to

support fourth phase• mobile CB used to transfer load• special techniques for voltage induction

TW = trapezoidal wire


case studies – increasing voltage rating

uprating double circuit 69 kV line to a single circuit 138 kV line

• crossarms replaced• double circuit conductors

arranged in twin bundles• number of insulators increased

from 5 to 9• line capacity increased from

100 MVA to 200 MVA• cost is 20 % of new line


case studies – upgrading structural

lattice steel towers following wind storm of 1999 in France

• towers &foundations to be reinforced using kits• panel bracing & increase to size of angles• micropiling foundations employed• some 18,000 converted to anti-cascading towers

example of 225 kV tower upgrade


case studies – upgrading electrical

steel towers for improved lightning performance

• reduction of line outages due to lightning strikes• selection of differing OHEW shielding angles• adjustment of geometry of the OHEW peak

OHEW – overhead earthwire


case studies – refurbishment

concrete foundations of 150 kV OHL

• degradation of concrete due to ASR (alkali-silica reactivity)

• foundations excavated• temporary foundations used to

support load• in some cases existing foundations

removed• new foundations installed


case studies – refurbishment

ceramic long rod insulators on 400 kV OHL

• non visible cracks develop up to complete peeling off of a slice of ceramic body

• duplicate insulator design avoids dropped conductors

• replacement of failed insulators during an outage


case studies – asset expansion

adding communication equipmenton top of existing towers

• structural analysis• mounting of platform• mounting of antennas• installation of control equipment• require external AC supply• revenue income commence


questions

• difficult, time consuming & expensive to construct new OHL• third party interest in using existing OHL assets• optimum technical and economic options• consideration of optimum time for project• many different options to increase utilization of existing OHL

conclusions

TB is for Asset Managers and Executives


acknowledgements

Keith Lindsey, WG Convenor, USA; Gary Brennan, TF Convenor, Australia; Rob Meijers, Secretary, Netherlands

Regular membersRegis Clerc, France; Rafael Garcia Fernandez, Spain; Detlef Hussels, Germany; Zibby Kieloch, Canada; Henning Øbro, Denmark; Yrjö Ojala, Finland; Steinar Refsnæs, Norway; Jiri Steinbauer, Czech Republic; Fernando Witbooi, South Africa

Corresponding membersRikus Bekker, Australia; Magdi Ishac, Canada; Peter Tarczy, Hungary; Irena Kuczkowska, Poland; Glen van der Wijk, former WG Convenor, Netherlands; Gilbert R Marshall, United Kingdom; George Niles, USA; Finn Rimmer, Canada; Jan Rogier, Belgium; Marius van Rensburg, South Africa; Ed Shantz, Canada; Anand Goel, Canada; Peter Fiers, Austria, Andy Stewart, USA.

ReviewersJoao Felix Nolasco, Brazil and Sven Hoffman; United Kingdom.

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