A 52 kV transmission line replacement project currently underway in the southern part of the island of Öland will see E.ON’s first deployment in Sweden of covered conductor in a high voltage application (having previously been used by E.ON predominantly for 20 kV lines).
The covered conductor for the 12 km Öland line is being supplied by Amokabel and the installation contractor is ONE, with completion expected in October.
Why covered conductors?
One driver behind the Öland installation, which is in a protected area, is reducing the potential harm to birds and other wildlife arising from bare conductors. The covered conductors are also better able to cope with severe weather and the coastal location.
E.ON will be looking for a significant improvement in line reliability, with the existing, bare conductor, line experiencing no less than six outages in the past year or so.
System reliability is of course a key preoccupation for E.ON, and E.ON spokesman Björn Persson notes that even if you are in deep countryside (as the Öland line is) you are entitled to reliable power and increased amounts of it as electrification gathers pace.
The design of the new cable for Öland, builds on Amokabel’s extensive experience worldwide with what it calls “new generation” covered conductor technology.
Thanks to its low weight it has proved possible to use the existing poles and cross arms of the Öland line, and installation has proved to be straightforward, as confirmed by ONE, with a team of just three people able to carry out the work on each pole.
The insulation is highly effective but relatively thin, enabling electrical connections to be made using insulation-piercing connectors, able to penetrate the covering and contact the conductors without the need to strip the cable – meaning that making connections is more or less the same as working with bare wire.
For Peter Eriksson, CEO of Amo Kraftkabel, the significant thing about the Öland installation is the voltage. Amokabel’s covered cable has been widely perceived to be a medium voltage technology and “I think the market has not been aware that we have products also for high voltage,” he says.
In an ideal world, cables would be placed underground, but this is expensive and not always feasible. Peter notes that covered conductors deliver many of the benefits of undergrounding, but without the exorbitant costs. He also notes that the cost of underground cable increases roughly exponentially with voltage. “For high voltages the insulation has to be really thick, and the cable manufacture entails a vertical extrusion, requiring you to build high towers.”
In contrast, for covered conductors installed overhead there is only a “slight” price difference between the 20 kV and 52 kV cable, he says.
Overall, installation time for the 12 km Öland line was around seven weeks and the total project cost was around 4.7 million SEK.
Cable design
The Amokabel covered conductor employs three layers, Peter explains. The first is a semi conductive layer applied to the aluminium strands. This creates a more evenly distributed electrical field, reducing electrical stress on the insulation. The second layer consists of high-grade electrical insulation, while the third is a robust outer jacket tailor made to suit local conditions, eg high UV in Australia and the Middle East, low temperatures in Sweden.
A USP of the Amokabel process is a “water blocking” step, so the cable is “100% water tight from the beginning,” notes Peter. With other covered conductor designs water can find its way in and propagate quite a long way, even as far as the midspan. In cold conditions, such as those encountered in Sweden, “this water can freeze and potentially crack the insulation.” But this certainly won’t be happening in the Öland line.
E.ON views the Öland covered conductor project as a pilot and “we will see how it works”, says Björn Persson. “If, after one or two years of operation, we get good results, then of course there will be opportunities to carry out similar projects at other locations on the island and elsewhere in Sweden.”
Amokabel covered conductors worldwide: some recent developments
Looking at the adoption of covered conductors worldwide, the drivers, which vary from country to country, can include the following: distribution network outage reduction; bushfire prevention; wildlife protection; electrical safety (not least for line crews); avoidance of conductor corrosion, in particular for seaside sites; and, last but not least, the possibility of more compact installations because insulated lines allow phase-to-phase distances to be reduced.
The technology is well established in Scandinavia, Amokabel’s “home turf”, particularly for power lines serving remote communities in heavily forested regions, with the aim of avoiding faults due to weather, trees falling and wild life (as in the Öland case).
Among key potential markets is Australia, where the focus is on reducing bushfire risks and improving grid reliability. Replacement of bare conductors in the country’s extensive SWER (single wire earth return) network represents a significant opportunity to eliminate bushfire risk in large parts of rural Australia at an extremely attractive cost, says Amokabel.
In the past, Australian DNOs have tended to focus on pilot projects, rather than full commercial roll-out of covered conductors.
But the technology is now considered proven. Cost is perceived as a barrier for some projects, but Amokabel would argue that in many instances a rigorous cost benefit analysis has not been done.
Recently, the company has been working on the provision of covered conductor to the Neika area of Tasmania, which is known for vegetation related distribution system outages.
In New South Wales there is also currently a covered conductor project in full roll-out mode, albeit at relatively small scale.
One factor working against adoption of covered conductors in the Australian state of Victoria has been the major investment that has occurred there in REFCL (Rapid Earth Fault Current Limiter) technology, but this has its limitations says Amokabel and is only applicable to three phase supply, and not to SWER.
Looking to the longer term, in 2022 Amokabel acquired Euro-Tech Cables as part of a plan for Australian production of covered conductor.
Meanwhile, in India, very positive experience has been reported by Karnataka Power Transmission Corp with 66 kV Amokabel covered conductor, including a right-of-way reduction from 18 m to 5 m in urban areas.
Covered conductor has also been adopted in India along wildlife corridors, where, for example, elephants feed on leaves growing at a level similar to power lines.
In the Middle East covered conductors are employed in coastal desert areas to address erosion/corrosion problems, eg arising from sand storms.
The USA is proving very conservative and slow to adopt “new generation” covered conductor technology, with the power distribution industry working to standards that result in much heavier covered cable, making it difficult to use in reconductoring projects. But, potentially, it of course represents a very large market.
