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

Burnie-Waratah 110 kV Transmission Line Wood Poles
TNM-CR-808-0888
Issue 1.0, November 2008
In 2006 an evaluation 1 was conducted into replacing the wood poles with steel poles, as and when
they were condemned. The report looked at 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. However, the benefits of steel structures in
comparison to wood structures are numerous including:
(a) improved resistance to fire (both pole and pole top);
(b) unlike some wood poles, steel poles do not leach chemicals into the soil;
(c) greater availability; and
(d) significantly lighter than wood poles.
The only negative aspect of a steel pole is the potential for corrosion. However, through the
utilisation of galvanised surfaces, top and bottom pole caps, and HDPE sleeve at the ground to air
interface, the risk of corrosion is sufficiently mitigated, resulting in a life expectancy of
approximately 75 years.
Due to these advantages, Transend investigated whether further cost savings could be obtained
through the replacement of two wood poles with a single steel pole. It was found that this was
technically feasible and the cost per suspension tower replacement was approximately 16 per cent
cheaper than utilising two wood poles.
Based on this evaluation it was decided that a new structure using only one steel pole would be a
viable alternative for suspension structures with the two steel pole replacements being adopted for
the strain structures.
2.4 SPARE PARTS AND CONTINGENCY PLANNING
Transend has a small number of steel poles to cater for contingency events and can source wood
poles from local suppliers in emergencies.
2.5 SAFETY
As detailed within Transend’s Transmission Line Support Structures Asset Management Plan
(TNM-SY-808-0223), the risk of some aged wood poles failing and causing the transmission line
conductor to fall and either cause a fire or expose line workers or the public to a safety hazard is
high. The risk mitigation actions recommended in this instance are to inspect, test and replace
(where needed) affected structures.
2.6 ENVIRONMENT
Environmental risks include the possibility of a bushfire start and the inappropriate disposal of the
Copper Chrome Arsenate (CCA) 2 impregnated wood poles.
3 ASSET MANAGEMENT OPTIONS
The costing comparisons associated with the following options are contained in the 2006
evaluation report (see footnote 2).
1 Hydro Tasmania Consulting report ’110kV Burnie-Waratah transmission line comparative cost study of
Sureline Steel poles as an alternative replacement for condemned wood poles’ dated 7 June 2006.
2 CCA is a mixture of inorganic components containing the elements copper, chromium and arsenic. Lebow
(1996) explains that the primary role of chromium is in CCA fixation, through a complex series of reactions
driven by its reduction from the hexavalent state to the trivalent state after it is applied to the wood. Copper
and arsenic provide the efficacy of the preservative, copper primarily as a fungicide, and arsenic more for its
activity as an insecticide, and also for activity against copper-tolerant fungi. Cookson (2001) claims that
while arsenic was originally thought to be needed for insect control, the latest theory is that arsenic is more
useful in controlling copper-tolerant brown rotting fungi.
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