Transend - Appendix 5 Renewal capital expenditure - Australian ...

Burnie-Waratah 110 kV Transmission Line Wood Poles
TNM-CR-808-0888
Issue 1.0, November 2008
EXECUTIVE SUMMARY
This document assesses the condition of Transend’s population of wood poles currently installed on the
Burnie–Waratah 110 kV transmission line.
The Burnie–Waratah 110 kV transmission line was commissioned in 1967 and was constructed as a
single circuit ‘H’ pole line with each support structure comprising two treated hardwood poles and a steel
crossarm. The transmission line currently has 422 treated wood poles (two per structure) and 14 steel
poles (one per structure) installed at 223 locations. The wood poles have installation dates ranging from
1966 to 2001.
The wood poles are tested every three years, with the next test regime to commence during summer in
2010-11. These tests are undertaken by contractor Aurora Energy Pty Ltd (Aurora). Aurora is considered
by Transend as the treated wood pole experts in Tasmania; in that it successfully manages a population of
over 250 000 wood poles. Transend consequently utilise Aurora’s proven pole testing methodology.
The treated wood pole failure rate for this transmission line when compared against the HEC/Aurora
historical and estimated treated wood pole failure rate shows that the wood poles on this transmission line
are failing at a faster rate (Trim Ref D08/68430). The earliest installed treated wood poles on this line are
now 42 years old, and the estimated failure curve indicates that the last original treated wood pole on this
transmission line will be replaced in 2033 (67 years old) as against 2039 (73 years old) from the
HEC/Aurora data. The actual failure curve when forward estimated indicates that at least thirty poles,
installed in 1966, are expected to require replacing in each future three yearly inspection cycle.
During the 1980s the wood poles were reinforced by attaching a separate shorter pole to the existing pole
as a support. This approach was found to be ineffective in providing sufficient support when it was
identified that the internal weakening of the original pole was not only at or below ground level but also
extended well into the upper portion of the pole. The internal weakening was also not limited to rot, but
included a fungal attack through cracks of the outer surface of the pole as it weathers and ages. As such,
reinforcement of an existing weakened pole, either by a separate supporting pole or metal stakes at
ground level, is no longer recognised as a technically viable life extension option. Since the 1980s and
until 2006, all condemned poles and the existing reinforced poles have been replaced with new treated
wood poles.
In 2006, an evaluation was conducted into replacing the wood poles with steel poles, as and when they
were condemned. The report considered replacing both wood poles in the structure with steel poles. The
report found that there was a whole of life premium of 14 per cent in replacing two treated wood poles
with two modern steel poles. Further analysis has identified that replacing two wood poles with a single
steel pole (for suspension structures) and two steel poles (for strain structures) is approximately 16 per
cent cheaper than the traditional method. This revised pole replacement methodology was adopted and is
currently being utilised.
The future management strategy is to progressively replace the wood poles on this transmission line with
steel poles, one at a suspension structure and two at a strain structure, as and when the wood poles are
confirmed condemned through testing.
Historical inspection and test results indicate that approximately 70 structures will be condemned and
require replacement in the next planning period at a total cost of approximately $4.6m dollars.
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