RECENT PROJECTS - BETS-CTN 66 kV LINE.

AVS provided a project report to Powercor in May 2005 which highlighted our conditional assessment of the assets and our recommendations. The report demonstrated capital cost savings of approximately $336,000 or 43% of the project cost to remediate these structures.

To quantify the maintenance requirements of the line we defined the safety and reliability boundaries. We developed a measure of Line Reliability (LR) that is a new and important attribute in the management distribution structures. As a result of this measure, asset managers can realistically endeavour to maintain the line so that the serviceability indexs are all kept above 1.1. This category now exceeds the normal serviceability spotlight and allows management to also focus on the reliability of a line.

We modelled the poles in our engineering system (Best Engineering ®) and observed that, with variations, in general the Charlton line was typical for well designed sub-transmission lines of similar age.

Thirty-four of the sampled poles (70%) had undergone special ground line preparation when first erected. The process involved chipping away the natural surface wood about the ground line zone, treating the exposed timber with creosote, and charring the new surface with a gas torch. Measurements taken for this study indicate that the practice removed an average of 3.5% of the original ground line strength, and reduced the service lives of the poles by 3 to 5 years.

We calculated the linear rate of decay (strength loss per year) of the structures to be 1.3 %. This rate is consistent with other distribution companies using the system of measurement, i.e. Auckland (1.25%).

From this data we modelled the strength groups, age profiles and the linear rate of decay. We predicted pole replacements, by our model, with the actual replacement numbers over the past 40 and 50 years. The predictions have a proved average accuracy of better than 90%.

Application of this modelling has high value for ongoing maintenance management and in the reliable forecasting of short and medium term capital requirements, and for planning and setting budgets.

Our assessment and analysis confirms that the Line was in serious need of major refurbishment and reconstruction works. Our model suggested that over the entire line, twenty-eight percent of the poles (staking excluded) were in need of urgent remediation work and only six percent were considered reliable.

We modelled the gains of staking, using a 120 kN system, which provided both a serviceability and economic benefit to these assets. Pole previously categorised as unserviceable had reduced by ninety-five percent (95%) and pole categorised as both unserviceable and limited life had reduced by fifty percent (50%) in total. Forty-five percent (45%) of the structures were now reliable.

We again introduced an innovative and complex equation for maximising life extension through staking. We included the BETS-CTN Line parameters to find the minimum residual SIs (and corresponding life extensions) for which the integrity of degraded poles can be restored by staking.

If the process above demonstrates that a structure, or group of structures, could not delivery an acceptable Line Reliability (LR) measure (have an SI of greater that 1.1) over a life extension period that is economically justified under normal business rules then replacement is the next option.

We now had the ability to define the actual new pole specifications. The natural average degradation rate of 1.3 (%Loss/Yr) gives us a basis on which to specify a standard pole of sufficient cross-section to deliver an acceptable service life.

We also plotted the reliability of the standard 70 year and 50 year poles over their lifetimes. We observed that the targeted reliability level (SI > 1.1) was exceeded for the first 60 years out of the forecast 70 year service life; and 40 years for the 50 year service life.

The BETS-CTN radial 66kV line is critical to the supply of Powercor's north-west area. Its importance is reinforced by its remoteness, customer sensitivity and lack of supply contingencies. This strategic course of action is focused on targeting critical CAPEX and OPEX funds to optimal outcome where the performance of this line is enhanced with every dollar spent.

This study proved the worth of this system in assessing the assets and defining the rates of decay and condition of the structures based on the Australian standard.

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