Most discussions relating to birds and power lines tend to focus either on bird mortality or on bird-induced outages. Past INMR articles on the topic, for example, have highlighted that the problem at distribution voltages is much different than on transmission lines and requires different solutions. In the case of distribution systems, the key problem is electrocution. One investigation estimated a density of electrocuted birds at 15 for every 10 km of line per year. By contrast, the central problem on transmission lines is flashovers caused by bird behavior after perching on a tower cross-arm. Before taking-off, they often release up to 60 cm of excrement mixed with conductive urine emitted at high pressure. This creates a conductive path that bridges the air gap between tower and conductors. The result is a flashover either in parallel to or near the insulator string. There is also the troublesome issue of ceramic insulator strings becoming progressively covered by conductive bird excrement and requiring washing to reduce flashover risk.
But not all bird problems involve threats to protected species or impact a line’s performance. In the case of woodpeckers, the key issue is progressive deterioration in sheer and bending strength due to holes pecked into wood pole framing. There are several theories as to why these birds find utility poles so attractive but most researchers conclude that they present a convenient vantage point for announcing territory and detecting predators.
One power utility that faces the challenge of woodpecker damage is FortisBC, located in Canada’s westernmost province of British Columbia. INMR meets with engineers to review how this problem is being assessed and addressed.
According to Engineering Manager, Aram Khalil-Pour, the normal life of a wood pole in the service area of Fortis- BC is between 50 and 60 years. However, in extreme cases of woodpecker damage, some wood pole structures have seen woodpecker damage and this potentially could impact lifetime of wood poles. This makes these birds more than just a nuisance and in fact an asset management challenge that must be dealt with properly.
Khalil-Pour explains that FortisBC conducts assessments of all its overhead lines on an 8-year cycle. This includes both below grade and above grade inspections of each structure. Apart from checking samples of wood poles below grade for issues such as moisture penetration, visual assessment is performed of structures, cross-arms, line hardware and conductors.
Recently, this inspection protocol highlighted what appears to be a growing problem with woodpecker damage. For example, during the 2015 and 2016 condition assessment of lines, a large number of structures were identified as having woodpecker holes. This initiated broader discussion about how woodpeckers may be affecting the system. Khalil-Pour states that current practice is that line inspection personnel in the field assess the extent of woodpecker damage to poles and decide whether to replace an affected structure or whether more detailed inspection may be required. Moreover, starting 2017, data on numbers of woodpecker holes is being systematically collected and will be studied each year to determine whether the problem is stable or increasing, due to possible factors such as climate change.
Another topical issue is how best to deal with poles where there are already holes but where there is no perceived urgency for replacement. Khalilpour points out that up to now there have been no cases of poles that failed mechanically due specifically to woodpecker damage. This suggests that the problem is not at a critical stage but rather still a potential threat that must be monitored and assessed.
One remedial approach tried elsewhere in Canada has been to fill holes with a special compound to prevent the pole’s interior being exposed to climate and ageing prematurely. But Khalil-Pour sees little real benefit along with several possible problems. “The filler material does not contribute to restoring the lost mechanical strength of a pole,” he says, “and may actually result in new holes in the future if woodpeckers come back to nest and find earlier holes filled. There are environmental concerns as well.”
In terms of measures to prevent the problem in the first place, a number of devices have been evaluated to discourage woodpeckers from alighting on pole framing. These include so-called ‘eagle eyes’ as well as rotating shiny wheels since it has been suggested these birds avoid reflected silver light. However, one photo captured by Khalilpour shows a woodpecker in the process of pecking a hole only a few feet above just such a wheel. Moreover, his experience is that these devices are not durable and fall off over time.
Another potential measure to protect wood poles from woodpecker damage is wrapping them in steel mesh, as proposed by other utilities. However, Khalilpour expresses concern about how a steel fabric wound over a wood structure will impact its electrical properties and worker safety. “It effectively turns the wood pole into a steel pole and changes its BIL. There are also related grounding and bonding issues. Finally, the mesh could affect ease of climbing. It’s not cost but rather perceived risk that tips the balance against such a solution.” Khalilpour has also evaluated using a plastic mesh but wonders how long these will survive if damaged by repeated climbing. Another doubt is whether the material can stand up to high UV and weathering.
Wood pole framing is common on transmission networks in Canada and indeed across the globe because it offers easy access for lines workers. Changing to steel or concrete is an obvious solution to avoid woodpecker damage but for FortisBC comes with the challenge of transporting and erecting much heavier structures, often at remote sites. Moreover, both materials offer less BIL than wood and thereby change a line’s electrical characteristics.
Yet another option, notes Khalil-Pour, is composite fiberglass poles that are light and offer lower installation costs but can be up to three times more expensive than wood. Delivery lead times can also be problematic due to fewer suppliers. Apart from these disadvantages, such structures are also more difficult to climb and often require use of a bucket truck for maintenance. Nevertheless, Khalil-Pour feels they do present a longterm solution for high problem areas, looked at on a case-by-case basis.
In the meantime, even as data is being collected to evaluate the number and growth rates of woodpecker holes, a pilot project has been launched to investigate another solution – wrapping poles in a special polymeric material, purpose designed for this type of application. Sourced from a supplier on the U.S. west coast, Khalil-Pour says that these wraps are easy to install, it is believed they have no impact on a pole’s BIL and create no new grounding or bonding concerns. The wrap, which has been tested in the lab for UV and weathering performance, also it seems it does not affect worker access to the pole or create additional safety issues. As part of this pilot project, FortisBC will evaluate the effectiveness of this wrap. With this new remedial measure in place, Khalil-Pour explains that FortisBC will have a range of options once poles with woodpecker holes have been identified during inspection cycles. “We may decide that the problem is too small to worry about or that it is better to wrap the pole because it seems a target for ongoing damage. In more critical cases, where there is already significant damage, we can replace the pole either with wood or composite types. The choice here will depend on criticality of line and ease of access to the site for our installation crews.”