Around the world, the availability of electricity has become part of the standard of living. The transport of electricity from power plants to end users is mainly through overhead transmission lines. Worldwide population growth is resulting in the spread of habitation even in some of the most remote areas. The majority of overhead transmission lines constructed to date can pose increased risks for birds, significantly affecting their habitats, namely, in their breeding, staging and wintering areas.
The government of Uganda, through the Uganda Electricity Transmission Co. Ltd. (UETCL), proposed extending an existing 132-kV transmission system from the planned 220/132-kV Mirama Hills substation to a new 132/33-kV substation situated about 10 km (6.2 miles) northwest of Kabale. Due to a combination of factors, only a few remnants of the rich wildlife in the form of birds and smaller animals can be found in the area proposed for the Mirama-Kabale transmission line in Uganda.
During preliminary line route surveys, several specimens of Crested Crane, the official bird of Uganda, were observed in valleys in the hilly areas near Mirama and in the mountains near Kabale. The utility considered it mandatory to protect these birds. Therefore, to ensure the proposed transmission line complied with the environmental requirements of the area, the geometry of the line had to be adapted and the conductors had to be equipped with special devices to provide bird protection.
Bird Impacts with Lines
Migratory birds can suffer mortality as a result of a collision with structures built to provide public services and amenities. Three such entities are increasing nationwide: communications towers, transmission line supports and wind turbines. Collisions with transmission system and distribution network overhead lines can kill many birds annually, in addition to birds that get electrocuted. However, utilities are generally poorly monitored for both strikes and electrocutions, so no annual statistics are available.
The three main impacts of transmission lines on birds and their relevance to this project are habitat destruction and human disturbance, collisions and electrocutions.
• Habitat destruction and human disturbance. Because of the routing of overhead lines adjacent to main roads, there is no destruction of the important habitats for birds. However, some woodlands and individual trees will be removed. Since most of the bird species recorded in the project area were widely distributed, the clearing of vegetation along the overhead line corridor was unlikely to cause a major impact on the species’ habitats. Furthermore, the only near-threatened species recorded in the wider region, the Crested Crane, has its home range in wetlands, a type of habitat not common in the project area.
The transmission line passes eight small wetland areas. The first six spans, identified with lengths between 350 m and 1,800 m (1,148 ft and 5,906 ft), were combined in one environmental section with a total length of about 8,500 m (27,887 ft). The towers in this section are designed to support a horizontal conductor arrangement, and the anti-bird devices will be installed on the six spans in the environmental section of the transmission line. The seventh span, some 1,700 m (5,577 ft) in length, is located in the middle of the line while the eighth span, of about 700 m (2,297 ft), is located close to Kabale substation. Thus, the initial eight spans comprise three sections.
• Collisions. A bird collision occurs when the bird physically strikes either the overhead line conductor or ground wire of the transmission line. It is generally accepted that birds usually avoid the highly visible bundled conductors but often fail to see the thin ground wire. The most important factor in determining collision impacts are the location of the line with respect to the roosting and breeding sites of birds. Because the most threatened species, the Crested Crane, does not have its most typical habitat in the project area, it is unlikely there will be an increase in the number of collisions involving this particular species.
The type of line also may be important for the extent of impacts. The proposed transmission line has a conductor height of about 30 m (98 ft) above ground level and is supported by lattice towers. Therefore, the 132-kV transmission line is likely to have a bigger impact on birds because of the large metal tower constructions at a height that may interrupt birds’ migratory patterns. However, other bird species tend to fly below a height of 10 m (32.8 ft) when moving around the savannah and bush land habitats.
• Electrocutions. Birds of prey are most commonly electrocuted on power lines because of their large wingspans. However, because of the type of double-circuit overhead line under consideration — 30 m (98 ft) in height — and the area it passes through, it is likely this impact will be moderate. There is a risk some common species of birds may be affected by the overhead line, mostly through collisions with the power line. This impact is likely to be negative and may be mitigated.
The 10.9-km (6.77-mile) 132-kV double-circuit Mirama-Kabale transmission line is designed with lattice-steel self-supported-type towers supporting a three-phase vertical conductor configuration to minimize the width of the line corridor. For bird protection, the towers were specially designed to accommodate a horizontal conductor configuration, equipped with protection devices installed on all conductors. This type of tower has two levels, the lower level for the phase conductors and the upper level for ground wire and optical ground wire (OPGW).
On all the towers with the phase conductors in a horizontal-plane arrangement, the top conductors, the ground wire and OPGW, and the extreme phase conductors were marked by the accepted bird protection devices. In situations where the ground wire peaks above the horizontal crossarms on the anchor towers, the steel structures of these peaks are painted black and white.
This transmission line for the Uganda project minimized the electrocution problem, the collision risk of birds and the impact of the overhead line on the quality of the line habitat. It is clear that sensible consideration of the routing of transmission and distribution overhead lines coupled with changes to tower constructions can effectively reduce the risks posed to birds.
Mitigation Bird Impact Measures
Consideration should be given to the installation of an inexpensive type of bird diverter, for example, markings or flappers on the transmission and distribution overhead line. The utility’s operator responsible for overhead lines should be tasked with the monitoring of bird migratory patterns to assess whether there is a risk of these being affected. If they are clearly affected, the operator should have a commitment to install the anti-collision devices.
Bird flight diverter fittings are a sensible and effective contribution to the protection of wild birds, since overhead transmission lines equipped with such devices substantially minimize the hazard caused by these lines. Markers on the ground wires and conductors enable large birds to see the line at a distance and take early action to avoid it. Bird flight diverters are available from numerous clamp and fitting manufacturers, offering the opportunity for competitive product marketing.
Bird Flight Diverters
Bird flight diverters can be static devices, dynamic devices, reflective devices and illuminated devices.
• The static device solution is installed at intervals of a few meters so they can be seen by birds. Static devices are mechanically more durable than dynamic devices because they lack the element of wear and tear inherent in equipment with moving parts. The static devices, called bird flight diverters, have had limited success.
• The dynamic device solution is installed at 20-m (66-ft) intervals so they can be seen by birds. Dynamic devices, usually called bird flappers, have moving parts as opposed to static devices. Dynamic devices are effective in reducing collisions because the birds seem to see them, probably because the movement attracts their attention.
When choosing between the static and dynamic solutions, the dynamic solution is recommended because it has been designed to minimize adverse effects on overhead line conductors. This also ensures the conductor remains visible in the event of conductor torsion. Optimized surface finishing reduces the risk of voltage discharges on the bird flight diverters, which would destroy the fitting.
• Reflective devices comprise a reflective stainless-steel sphere of 70 mm (2.75 inches) in diameter. Experiments have shown the visibility of this device to be superior to objects with other colors (red, yellow, white and black), especially during the low-light conditions at dawn and dusk, when birds may be flying from roosting areas to feeding areas and back. Because of the spherical shape, the device reflects any available light in all directions and, therefore, is visible from all directions, including above or below the diverter.
• The illuminated device solution is used for birds that fly at night. The device available for this problem is the Mace Bird Lite, which is a Perspex tube containing a fluorescent tube inside. In case of high-voltage overhead lines, only the middle 60% of each span needs to be marked, as this is where most of the collisions occur. The other parts, close to towers, are protected by the tower forms.
The proposed solution for the Uganda project was the bird flight diverter flags, which is a dynamic bird model. The bird flight diverter flags have been developed based on the findings of ornithological research and are considered to offer optimum effectiveness. As birds notice vertical structures better, all these fittings are designed with distinct vertical lines. The bird flight diverter flag has separate moving marking straps with a blinking effect and maximized contrast to make it even more noticeable.
The 132-kV transmission line project in Uganda crossed three main sections of an area that provided a habitat for special species of birds. To minimize the risk of collisions with the overhead line conductors, tower configuration was modified in these sections. A special family of towers was designed for these sections for the double-circuit overhead line. The towers had extended horizontal crossarms that could accommodate the three-phase conductors on each side of the tower.
The top conductors (ground wire and OPGW) and the extreme phase conductors were marked with acceptable bird-protection devices, usually a black-and-white warning-flag system. Additionally, insulator strings should be protected against pollution caused by birds by installing bird guards on tower members immediately above the insulator strings.
The durability of many bird-protection armatures must be significantly improved. Materials used must withstand all weather conditions and ultraviolet light for decades. Markers on high-voltage conductors also must be compatible with high electric fields and high heat input. In practice, worn out and damaged protective caps or markers are a nuisance. Until materials of acceptable long-term stability and durability for use on insulators and conductors are available, the construction measures employed on the transmission line for this UETCL project is likely to remain the preferred solution for all new overhead lines.
Stephen Kyeganwa ([email protected]) holds a BSEE degree from Makerere University and a MBA degree from Makerere University Business School. Since joining the Uganda Electricity Transmission Co. Ltd., Kyeganwa has gained extensive experience in grid planning, energy supply and demand analysis, major feasibility studies and construction management by being responsible for the 220-kV, 137-km (85-mile) Kawanda-Masaka transmission line. Currently, Kyeganwa is the principal monitoring and evaluation officer at UETCL.
Ecaterina Dragan ([email protected]) is a project manager at Fichtner Consulting Engineers, having worked as a professional in power transmission for more than 35 years. She specializes in preparing technical specifications, engineering, technical documentation, assessment of manufacturers, quality assurance and material inspections. She was a member of the CIGRE committees B2 — Overhead Lines and B2 WG 15 — Line Cycle Assessment.
Stefan Bühler ([email protected]) holds an engineering degree from Diplom Ingenieur TU Karlsruhe, and is a senior consultant and project manager at Fichtner Consulting Engineers. Bühler has worked on a number of varied major turnkey contracts that include high-voltage air-insulated and gas-insulated substations with Siemens and ABB, high-voltage transmission lines with NOK and combined-cycle gas power plants with Alstom, in addition to projects for the oil and gas industry.