The term wildlife protective device is relatively new to the power industry and refers to any device used on the network to reduce outages due to the impact of wildlife. Other terms sometimes used to describe these devices include animal guards, bird guards, bird deterrents, to name a few.
This INMR article from 2010, contributed by Jonathan Woodworth, provided an overview of such devices used to reduce power system outages caused by wildlife. Design considerations, testing methods and installation issues are all covered.
Devices used to mitigate the effect of wildlife on power systems have been in existence for many decades now. Figure 1 shows an example of such a wildlife protective device (WPD) used on an arrester.
In fact, WPDs are used not only on arresters, but on all types of equipment where animal contact between earth and the high voltage side of the insulator is possible. Figure 2 shows WPDs on a distribution system recloser bushing as well as on the arresters
Standards & Guides
IEEE 1656 is a Draft Testing Guide for WPDs, as yet not published but already in the final balloting stages. The Guide defines WPDs as “A device, guard or structure providing electrical isolation from high voltage equipment that is intended to prevent contact by wildlife that would result in a momentary flashover or short circuit of the electrical system. Contact by wildlife should not produce physical harm to either the equipment or wildlife.”
This Guide, which was initiated in an attempt to eliminate ineffective designs, will be the first ever on how to test WPDs in order to verify their quality, effectiveness, capabilities and environmental withstand. When published later this year, it will become the only document that covers this important topic anywhere in the world. The focus is entirely on wildlife guards up to 38 kV, which seems appropriate for this type of device since equipment in this voltage range is short enough that the potential for wildlife contact between the HV end of the insulator or bushing to earth is reasonably high. At voltages above these levels, insulator length and spacing is usually great enough to make such a device much less necessary.
A second and equally valuable document is IEEE 1651 titled “Draft Guide for Reducing Bird Related Outages.” This Guide, also in the final balloting stages and not yet published as such, focuses on avian (birdrelated) issues and contact with power systems. It is not a testing guide but rather an application guide and, when published, it will provide an excellent overview for transmission system operators on how to deal with all bird contact issues. One WPD discussed in detail in this guide is the deterrent to the highly conductive streamers caused by defecating birds.
There do not yet appear to be any IEC documents that deal with WPDs but this is likely to change very soon. A presentation on the issue is scheduled at the next meeting of CIGRE Working Group A3.25 (in March of this year) to begin work on the subject.
The Edison Institute in the U.S. has published a comprehensive guide relative to this subject, titled “Suggested Practices for Avian Protection on Power Lines – The State of the Art 2006” and is available at www.aplic.org
Benefits of Wildlife Protective Devices
There are several benefits of applying WPDs on power systems, the first of which is that effective installations will result in lower outage rates caused by animal contact. According to a National Rural Electric Cooperative Association (NRECA) survey in the United States, animals are the third leading identifiable cause of power outages and birds cause more transmission line outages than any other animal. For example, a wildlife protective device improvement program was initiated at Duke Power (a major American utility) more than 15 years ago. Since that time, outage rate due to animals has been reduced significantly. While the robust guards may appear much larger than necessary (as it can be seen in Figure 3) stocking only one size for all applications is more cost effective. Indeed, as per an article in T&D World (Sept 2004), author Joe Kysely at WE Energies claimed a US$ 27,000 savings realized annually by eliminating wildlife flashover on arresters alone by means of effective WPDs
A second benefit is reducing electrocution of animals. This is particularly important for species that are on the protected species list such as certain vultures and raptors. It is illegal to cause the death of an eagle in the United States, yet power systems that are not well equipped with WPDs can do just that.