BIRDS ARE A MAJOR PROBLEM FOR UTILITIES. They collide with overhead structures and conductors, contaminate insulators and equipment, and damage facilities leading to customer interruptions. On the flip side, birds don't always get hospitable treatment from utilities either. They are electrocuted, maimed and not so gently encouraged to stay off certain areas of our T&D system.
Utilities need to find better ways to cohabitate with birds so that the impact of their flight, perching and nesting habits leads to minimal power disturbances. Preventative measures also should be taken to safeguard birds, especially the more than 800 species of protected migratory birds in North America.
Birds cause damage and disruptions in many ways. Their size, type and habitat all contribute to the potential negative impact they can have on the power grid. Larger predatory birds like raptors cause some of the more challenging problems.
The Edison Electric Institute identified reasons why raptors are attracted to power lines: Poles increase their range of vision and attack speed when hunting; they provide good hunting and roosting platforms; they are favorable sites for raptors to broadcast territory boundaries; and a good prey base exists along rights of ways.
The contributing factors for raptors becoming electrocuted were identified as:
Large raptors like golden eagles, red-tailed hawks and great-horned owls are more susceptible to electrocution.
Juvenile raptors lack the experience and flight control of adult birds and, as a result, are more frequently electrocuted than adults.
Compared to the wingspan of raptors, the relatively close separation between conductors and conductors-to-ground is one of the leading causes of electrocutions.
Other large, heavy-bodied birds such as herons, cranes, swans and pelicans are also frequently reported casualties because of their large wingspans and lack of agility. Many species of ducks are vulnerable when flying at low altitudes because of their high flight speed. Flying in flocks also restricts maneuverability.
Woodpeckers destroy wood poles, causing structural failures. Parakeets are known to destroy the housings of polymer insulators. In stations, birds cause outages by attracting predators like cats, raccoons and snakes. On distribution lines, birds are responsible for nearly 25% of all outages in the United States. A 1990 IEEE survey reported that 86% of the utilities that responded indicated birds caused major problems in substations, second only to squirrels.
Birds can cause insulator flashovers due to their long streams of stringy, conductive and semi-liquid excrement. Contamination flashover of insulators occurs due to the accumulation of bird droppings. Many times this also might be due to birds building nests in the gaps and on the structures in substations. Nesting causes outages in other ways as well, such as when birds drop nesting materials, contact live conductors while flying in and out of the nest, and attract predators and animals or bring large prey items to the nest, which bridges insulators.
Discussions about these kinds of problems led to the formation of a task force within the IEEE working group on Insulator Contamination and Dielectric Aging. The objective was to provide recommended practices to mitigate bird-related outages.
A common rural, three-phase 7.2-kV/12.5-kV distribution pole is a wooden tangent structure (Fig. 1a). Three-phase distribution tangent structures, without pole-top grounds or pole-mounted equipment, generally provide adequate separation for all but the largest raptors. Additional protection is required in areas with eagles and other large raptors.
The tangent structures can be framed to provide an additional 16 inches (40 cm) of clearance, bringing the total phase-to-phase separation to 60 inches (152 cm). Additional clearance required for eagles can be obtained by lowering the crossarm on new poles. Dropping a crossarm may require shorter spans or taller poles to maintain clearances, adding to the structure cost. Figure 1b shows a common alternative to dropping the arm is using a 10-ft (3-m) crossarm and lowering the arm only an additional 12 inches (30.5 cm). This provides the recommended separation without using taller poles and is the most economical method.
Where collisions are likely to occur, for example at river and wetland crossings, using crossarm construction with horizontal line-post insulators versus vertical conductor construction will reduce the incidence of collisions. If possible, sag multiple crossings to the same elevation and use specular conductors so the lines will be more visible to birds.
On transmission lines where overhead ground wires are often smaller wires than the phase conductors, and so are more likely to cause bird collisions, eliminate static wires and protect energized conductors with surge arresters where feasible. An alternative to removing overhead static wires is to mark the wire with devices like aerial marker spheres, spiral vibration dampers, conductor cover-up, swinging plates, bird-flight diverters and flappers.
Often, adequate separation cannot be achieved through spacing, so, alternative measures must be taken. These include bushing covers on apparatus, heat-shrink insulation, insulated wire, cover-up insulation, insulating paint, pole caps, insulated wire and fusing tape on bare conductors.
Some dead-end structures have directional changes and lateral taps. These structures can be especially dangerous to birds due to the bare jumpers used between circuits (Fig. 2). Insulating the jumper wires is the most common retrofit method but cover-up insulation can also be applied. Many of the poles require cover-up on the center phase jumper to allow safe perching. On some structures, jumper wires may need to be re-routed under crossarms to eliminate potential phase-phase contacts.
Transformer structures also can be lethal to birds due to exposed transformer bushings, jumpers, exposed grounds and cutout/arrester contact points. Retrofitting two- and three-phase transformer banks includes installing perch guards on the top crossarm, covers on the transformer bushings, insulated jumper wires, bird spikes between cutouts and arresters, and fusing tape on exposed connectors (Fig. 3).
Perch management attempts to control where birds land or nest on structures. These devices include various designs of perch guards, elevated perching platforms, metal needle wire spikes, nesting platforms, insulated disk barriers and plastic bird spikes.
Several devices are designed to discourage birds from landing at dangerous structure locations. It is important to note that perch guards do not always keep raptors off structures. Placing perch guards on the top of vertical construction can contribute to electrocutions since the birds may choose to roost lower on the pole, near energized conductors. Perch guards can also shift problems onto other line segments.
It is more desirable to allow raptors to safely use the structures rather than shifting them off preferred perches to other structures that may be more lethal. It is also difficult to predict if artificial perches will be successful. Nesting platforms have been used successfully throughout the Western states.
Installing after-market products can lead to new problems. For example, bushing covers are used to cover up exposed bushing termination points on transformers, regulators, capacitors and reclosers. These are generally made of track-resistant polymers that either snap on or slide over a bushing top. No uniform standards exist for bushing covers. Some are more resistant to UV and environmental degradation than others. Some bushing covers also include a matrix of small holes to allow moisture to drain. Small birds have been observed probing these covers for the insects, resulting in additional electrocutions.
Wire-marking devices that physically enlarge the wire act as wind-catching objects, encouraging icing in the winter and increasing the risk of wire and power breaks due to line tension and stress loads. The attachment of devices also may cause physical damage through abrasion to the conductors. However, the effectiveness of some marking methods that target specific species can hardly be questioned, and marking is justified if spans are determined to be dangerous to endangered and vulnerable species. If markers are employed, they should be spaced at 5-m (16-ft) intervals since collision frequency decreases when the space between wire-marking devices is short.
Streamer outages are more common on transmission than on distribution lines. Large birds, such as raptors, herons and cranes, cause streamer outages. Streamer outages have been found to exhibit certain characteristics, such as occurring between the hours of 11 p.m. and 6 a.m., where natural roosts such as trees are scarce, where food is abundant and where the center phase is involved; with a seasonal pattern; with an instantaneous relay operation and successful reclose; with flashed insulators; with burned spots on the upper hardware or structures; and with the presence of dead or injured birds near the structure. These can be used as a guide to attribute unexplained outages to bird streamers. If several of these characteristics are present, bird streamers should be suspected.
Figure 4 shows a typical bird-contaminated insulator in Arizona, having bird droppings — thousands of starlings and pigeons have been sighted in this area — over a period of several months. A series of flashovers occurred on a foggy morning. Apparently, natural washing was ineffective in removing the excrement. Very high values of ESDD was measured, 0.4 mg/cm2.
A different utility suffered outages from another scenario: a large flock (thousands) of blackbirds or starlings came to roost in a substation. The overnight accumulation of fecal contamination on the insulators caused an outage. Figure 5 shows the contamination in a substation in Nevada.
Another type of occurrence is a long-term accumulation of contamination at a site that attracts birds, such as at a dairy, which causes an outage with the onset of rain after a long dry season. Accumulative problems also occur at nesting sites. Individual birds can create serious problems in substations during nesting. Small birds, such as starlings and sparrows, are cavity nest builders and will build their nests in any small openings available. Nest-building activities in substations can cause outages in several ways. Bird contacts are possible in tight places where the energized equipment is close to grounded surfaces. Birds will sometimes drop nesting materials when flying into the substation, causing a short circuit. Nesting birds attract predators, typically raccoons, cats and snakes, which often cause outages because they climb through the station looking for nests.
Large birds cause streamer outages as well as nesting outages. Vultures, unlike most raptors, will form large roosts. Although the energized conductors are far enough apart to prevent wingtip contacts, the roosting vultures cause extensive contamination of the insulators with their droppings eventually causing flashovers. Ospreys and blue herons, and to a lesser extent, eagles and hawks, build very large platform nests on transmission poles and structures (Fig. 6).
Fig. 7 shows another illustration of nesting outages, caused by a red-tailed hawk nest. This stick nest is located on a dead-ended structure with a double crossarm, a favorite site for nesting. Leakage currents caused by fecal contamination attributable to the increased activity around the nest resulted in a fire that burnt the pole and crossarms.
If only a few poles are a problem, perching guards can be used (Fig. 8). Perch guards of various designs are available and have been used with mixed results. Large perch guards installed above the center phase are effective in moving the bird streamers away by 1 m (3 ft) or more. Caution is advised in the use of plastic perch guards or spikes because some will severely degrade due to the sun's UV, and once a flashover has involved plastic, the charred surface will become conductive, presenting future flashover possibilities. These burned devices should be replaced. Also, birds have been known to both nest within plastic spikes and break them.
If the structure has numerous places to perch, insulator shields are more effective. Some utilities use both perching guards and insulator shields to prevent birds from roosting directly above their insulators, but allow them free use of the rest of the structure.
Other ways utilities use to keep birds away from their stations include: ultrasonic sirens, gel repellents and visual scare devices such as plastic hawks and owls. These scare tactics have been shown to be temporarily effective, until the birds become accustomed to the devices. According to a 1990 IEEE survey, only 2% of utilities surveyed found them to be effective.
If the outage is due to overnight staging/roosting birds, little can be done to prevent this. The after-the-fact solution involves both wet and dry washing of the insulators. Corncobs along with walnut shells were used for this purpose. Tough areas have to be scrubbed with a brush.
The long-term accumulation of bird contamination by one utility was treated with larger insulators, barriers to prevent nesting and perching, and regular washing at these sites.
Ospreys, as well as vultures, eagles, hawks, owls and falcons, are raptors and protected by state and federal law. Raptor nests on transmission poles or structures cannot be touched without a federal permit. The most successful method of removing ospreys (after obtaining required permits) from transmission poles is to provide them with a nearby alternative, usually a dummy pole with a platform installed near the existing nest site. Figure 9 shows a successful application of this concept. This is an in-service illustration of an osprey utilizing an alternate nesting platform provided by one utility. The dummy pole has no conductors attached to it and is placed generally within 100 ft (30 m) of the power line. The platform is made taller than the line to make it the preferred perch.
Removing roosting birds in substations is tedious, time consuming and labor intensive. Since birds select the substation as a roosting site because it appears safe and comfortable, the utility must convince them otherwise. Regardless of the method, bird discouragers, pyrotechnics, noisemakers, lights or falconry, it will require the presence of a crew every day for a period of weeks. In addition, it will require frequent follow-up inspections to make sure the birds do not return.
Nesting birds require a different approach. Regular inspection of substations and prompt removal of bird nests is not always the answer. Once some types of birds select a nesting site, they will attempt to rebuild their nests as often as the nests are removed. Some utilities no longer remove nests from their substations. Instead, they keep the area cleared of nesting materials dropped by the birds and carefully trim any loose material from the outside of the nests. If the birds have successfully built a nest without causing an outage and the utility chooses not to disturb it, the utility should install climbing guards and “snake fences” to keep out raccoons, cats, opossums and snakes. When the birds have raised their young and left the substation, the nests can be removed and the area can be screened to prevent nest rebuilding the next year.
Birds are persistent and constantly trying to build and locate nests in substation structures and equipment. New and better ways are needed to dissuade nest building. Some of the previous methods tried include the use of propane guns, bird bombs, imitation owls, electronic noise makers and flashing lights, all to no avail to prevent roosting and nesting in the substation equipment.
Birds do not like light in the night. Using floodlights and keeping them on all night was successfully used by one utility to drive away thousands of starlings that were nesting in the substation and causing contamination flashovers on 500-kV capacitor banks.
A similar incidence occurred in another substation involving 500-kV series capacitor support insulators. The utility decided that both capacitor banks would receive dead-washes twice a year, once in the spring prior to peak summer loading and again in the fall prior to peak winter loading. This periodic water washing or cleaning of the insulators has been beneficial in removing contaminants and extending the insulation strength of the insulators. IEEE Standard 957 gives guidelines and methods for cleaning insulators.
Insulator shields (Fig. 10) that completely cover the insulators have been reported to be effective in protecting the insulators from bird contamination. Another utility has been successful by changing out 115-kV ceramic insulators to polymers that have hydrophobic surfaces and longer leakage lengths.
Realistically, there is no practical way to permanently keep birds out of substations or off transmission structures. Knowledge of bird behavior and interactions is essential in understanding the effectiveness of the deterrents.
Transmission outages are costly. Insulators contaminated by bird droppings are expensive to clean. The cost of taking preventive measures is easily justified when compared to the expense of repairing or replacing damaged equipment coupled with outage time and customer impacts. Many utilities do not have adequate expertise with bird-related outages. However, there is good experience available in professional working groups and some of the larger utilities.
The authors would like to acknowledge these contributing members of the IEEE Working Group on Insulator Contamination and Dielectric Aging task force: J. Burnham, R. Carlton, E.A. Cherney, G. Couret, K.T. Eldridge, M. Farzaneh, S.D. Frazier, R. Harness, D. Shaffner, S. Siegel and J. Varner.
Raji Sundarajan is an associate professor at Arizona State University (Polytechnic Campus). She chaired the task force on bird-related power outages within the IEEE working group on Insulator Contamination and Dielectric Aging. She is a senior member of the IEEE. [email protected]
Ravi Gorur is a professor at Arizona State University (Tempe Campus). He served as chair of the IEEE working group on Insulator Contamination and Dielectric Aging at the time of the activity on bird-related power outages. He is a fellow of the IEEE. [email protected]