Transmission & distribution |
Tasmanian wedge-tailed eagle. This is among the challenges faced by the TasNetworks grid. Photo: Thomas Webster, TasNetworks
was because the insulation was damaged on a steel crossarm. In the other cases, we only had to switch the power off for as long as it took to cut the trees away. That means the impact on customer supply was reduced significantly as the outage was for only around one hour, rather than the four to six hours that is normally needed to repair an overhead line. Most importantly, none of these incidents resulted in a fire start.
full-scale installation of New Generation Covered Conductor (NGCC) from Amokabel, the Swedish cable manufacturer. This covered conductor has three layers of covering. A semi-conductive inner layer provides flexibility, a high-grade electrical insulator in the middle gives electrical performance and a tough polymer jacket provides protection. The outer layer needs to be particularly tough to withstand mechanical abrasion, as well as intense UV light. This fully sealed cable system prevents water ingress and meets the EN 50397-1-2006 international standard for covered conductors. An important feature is that the design life of NGCC is more than 40 years, which is comparable to bare wire.
The use of advanced lightweight insulation materials means that NGCC can be restrung on existing poles. This could help save TasNetworks, and ultimately our customers, the cost of replacing or adding infrastructure. We estimate that using NGCC is around 10% of the cost of undergrounding.
A study by CSIRO (Commonwealth Scientific and Industrial Research Organisation) found that this type of covered conductor reduces bushfire risk by 98%.
First field installation, at Neika The first full scale installation of NGCC was carried out at Neika, a rural locality about 10 km southwest of the city of Hobart. This rugged and heavily treed area is on the side of a mountain. It was selected for its significant vegetation, which has given it a reputation for outages and reliability issues.
The installation by our TasNetworks crew went very smoothly. Initially, the team was concerned about the NGCC being fragile, but they came to appreciate that it is quite robust. They found it easy to work with, appreciating that it was clean to handle and used the same tools as bare wire. The job took about the same time to install as bare wire, with no changes to equipment such as recovery trailers.
Since the installation was carried out in February 2024, we have had five instances of trees falling on the overhead line. One of these trees weighed 700 kg – according to the loadcell on the crane we used to lift it off – and it still didn’t result in an outage.
Only one of these treefalls resulted in a fault that caused an extended{?} outage, and that
NGCC cable drums. Photo: Amokabel/TasNetworks
Performance and cost Following on from the Neika project, we’ve started replacing HVABC with covered conductor. The first HVABC replacement was carried out at Ansons Bay, in the northeast of Tasmania. The feedback from the crew was so positive that they asked to set up additional NGCC lines in the area using the materials remaining from the original project.
It is too early to report in detail on
performance. However, the initial feedback is that outages have been reduced.
The trial projects have used 62 mm NGCC. Overall, the cost increase was estimated at around 20% compared with bare wires. This provides an excellent return on investment (ROI) in terms of improved network resilience and security of customer supply and reduction in risk to wildlife and fire start incidents.
At Neika, TasNetworks is well on the way to
recovering the additional cost of NGCC over bare wire.
Next steps
TN is currently planning NGCC installation at two more sites: Sisters Beach in northwest Tasmania to replace HVABC; and Launceston, a city in north Tasmania, to protect heritage trees. Overall, TN will replace 18 km of HVABC and 10 km of bare conductor to evaluate NGCC.
Then, providing there is positive feedback from the trial sites and distribution system designers{?} become comfortable with using NGCC, TN will focus on additional areas where wildlife is at particular risk or where salt pollution is a challenge. TN is interested at looking at NGCC for recloser leads and droppers, where it should be easier to work with.
A viable alternative
The experience from TN’s full-scale trials shows that the Amokabel covered conductor is easy to install and work with. It will allow TasNetworks to mitigate many of the potential risks that traditional open wire networks pose, at a reasonable cost, making it a viable standard replacement alternative. Reasons to install Amokabel covered conductor include reducing customer outages and their duration (reliability) and the incidence of fire starts.
NGCC, Neika. Photo: Amokabel/ TasNetworks
18 | September 2025|
www.modernpowersystems.com
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