Guidelines for Increased
Utilization of Existing Overhead
Transmission Lines
Electra - August 2008
WG 13 Management of Existing Overhead Lines
Keith Lindsey
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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
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background – why
• 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)
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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
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given the task of carrying out a project to
increase utilisation
asset managers and executives are interested in
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double circuit 110 kV converted
to single circuit 275 kV structure
technical brochure structure
general technical
and economic
considerations
asset
management
decision
uprating
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upgrading
refurbishment or
life extension
expansion
asset life definitions – technical end of life
•
OHL fails to perform within the normal operating requirements without
abnormal maintenance OR
•
OHL is no longer fit for the original purpose
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economic model of a transmission line – whole of asset life
capital cost of OHL
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asset life definitions – economic end of life
cumulative NPV costs
cumulative NPV of future annual cost of the line including losses,
maintenance, depreciation & risk costs per year of service is a minimum
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time from now
time
asset renewal economic optimisation
asset renewal project ΣNPV with a
designated financial and/or
technical planning horizon
maximum savings
in renewal costs
average long run
marginal costs of
asset renewal project
optimum time for renewal
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constraints
•
•
•
•
•
•
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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
uprating – increasing capacity
driver
thermal rating by
action
installing
increasing
adopting
redesign
voltage rating by
increasing
proposition
larger conductors
additional conductors
active line rating systems
conductor tension
conductor attachment height
probabilistic ratings
high surge impendance performance
insulation strength
conductor attachment height
net result - risk increased
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upgrading – improving reliability
driver
action
proposition
structural performance by
increasing
structure strength
foundation strength
electrical performance by
improving
insulation pollution performance
lightning performance by improving insulation
lightning performance by improving earthing
lightning performance by installing earthwires
structure potential rise
electrical induction
surge diverters
reducing
installing
net result - risk decreased
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refurbishment – restoring to design working life
driver
arrest degradation by
action
restoring
proposition
structure strength
foundation strength
conductor strength and capacity
insulation pollution performance
fitting strength
lightning performance
insulation pollution performance
net result - risk decreased
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asset expansion
driver
improve availability by
providing third party access by
action
increasing
installing
proposition
maintainability by adopting live line design
telco equipment
net result - risk varies
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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
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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
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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
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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
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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
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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
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case studies – asset expansion
adding communication equipment
on top of existing towers
• structural analysis
• mounting of platform
• mounting of antennas
• installation of control equipment
• require external AC supply
• revenue income commence
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conclusions
• 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
TB is for Asset Managers and Executives
questions
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acknowledgements
Keith Lindsey, WG Convenor, USA; Gary Brennan, TF Convenor, Australia; Rob
Meijers, Secretary, Netherlands
Regular members
Regis 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 members
Rikus 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.
Reviewers
Joao Felix Nolasco, Brazil and Sven Hoffman; United Kingdom.
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