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. raji@asu.edu

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. ravi.gorur@asu.edu