Performance Attributes for Cover Type Wildlife Protective Devices
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INMR Issue 102.indd 82
Q4 2013
WILDLIFE PROTECTION DEVICES
11/11/2013 10:14 PM
Performance Attributes for Cover Type Wildlife Protective Devices The concept of wildlife protective devices (WPD) is hardly new to the field of power engineering. Products aimed at reducing outages triggered by birds and other creatures have been around for decades and found application on all types of equipment – from bushings to arresters to cutouts, etc – indeed wherever there is risk of wildlife contact between earth and the high voltage side of the component.
Wildlife article
These days, with growing appreciation of the extent of this problem – estimated to cost between US$ 20 to 30 billion each year in the U.S. alone – and faced with possible heavy fines in cases of electrocution of protected species, the power supply industry seems more interested than ever to apply such devices. The recent availability of IEEE application guidelines and test procedures for WPDs has only accelerated this trend.
This article offers examples of the diversity of cover type WPDs now being installed by power companies across the United States and also discusses some of the considerations that determine effective long-term performance.
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Example of impact of wildlife intrusion on unprotected arresters. Similar arresters protected against wildlife (bottom)
Photos courtesy of FortisBC
The scale of the problem of wildlife interaction with overhead lines is alarming. For example, tens of millions of birds are believed to die each year due to contact with power lines and energized pole top hardware. This tragically high bird mortality is however only one side of the problem since such interactions also adversely affect reliability. For example, service experience from countries such as Germany and Russia suggests that up to threequarters of all outages affecting overhead lines can be directly attributed to birds. Even with successful automatic re-closure most of the time, power engineers and maintenance staff are still concerned, given today’s requirements for power quality and availability as well as internal rules among utilities on average outages permitted per 100 km of line each year.
Fortunately, the threat posed to distribution lines by birds and other creatures has been well documented and there is a large body of knowledge on how best to overcome or at least significantly reduce the problem. Typically, this requires insulating conductors and hardware close to towers using a range of protective devices of different shapes. These vary in design, materials and cost from simple generic devices that increasingly come preinstalled on transformers and other equipment to more specialized products, custom-designed for the application and made from high-performance insulating materials. One of the principal requirements for WPDs is that they have a service life similar to that of the components they are intended to protect. In this regard, they must be Photos: INMR Š
These WPD solutions may not win awards for aesthetics but seem to meet key requirements for effective installation and longterm performance. 84 INMR Issue 102.indd 84
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resistant to deterioration and ageing from weathering and UV. Another requirement, given their exposure, is that they be installed so that they do not easily dislodge or shift position under high winds or other loading. A few years ago, IEEE issued two engineering standards that offer guidelines on how best to protect lines and electrical devices from the adverse impact of birds and other wildlife. The first – IEEE 1651 "Guide for Reducing Bird-Related Deaths" – covers methods, techniques, and designs to mitigate power interruptions and equipment damage resulting from interactions of birds with electrical infrastructure. The standard addresses a spectrum of problems from electrocutions to collisions to nesting issues. It also deals with outages caused by fecal contamination and streamers. The second standard is IEEE 1656, "Guide for Testing the Electrical, Mechanical, and Durability Performance of Wildlife Protective Devices on Overhead Power Distribution Systems Rated up to 38 kV". This applies specifically to wildlife protective devices installed on overhead distribution lines and offers recommendations on testing products that are in direct contact with or in the proximity of energized parts and conductors.
Photos: INMR ©
One of the goals of this document was to eliminate ineffectual designs by providing methods to test products for quality, performance and environmental withstand. The focus was placed on wildlife devices up to 38 kV since equipment in this range is short enough that there is sufficiently high risk of potential for wildlife contact between the HV end of the insulator or bushing and ground. At higher voltages,
These WPD installations seems to present potential problems from unprotected components to exposed leads to covers that appear to have shifted under wind.
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WPD seems to have melted leaving arrester exposed (left & bottom).
insulator length and spacing is typically enough to make such a device far less necessary. IEEE 1556 presents effective methods to determine the withstand level of electrical apparatus equipped with wildlife protectors in order to verify that they meet the performance claimed. For example, one simple technique, the moving electrode test method, sees the WPD assembled on a test fixture or in its actual end application and energized. The power frequency voltage on the HV side is raised to 120% of that expected in service. A grounded contact is then moved around the protected side of the WPD. If there is no flashover after covering all protected surfaces, the device is considered to have Photos: INMR Š
WPD must not only cover but also ensure that the critical flash area of the energized component is not compromised. 88 INMR Issue 102.indd 88
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passed. Such a test effectively reveals the impact of even small seams in the product and demonstrates that it is incorrect to believe that covering alone guarantees protection. Also introduced in this same standard is a test that requires the WPD to withstand a continuous 60 mph (100 km/h) wind and remain attached to the component it is protecting. The most common type of WPDs cover the HV end of an insulator or similar component such as surge arrester or fuse cutout. They may appear simple to install but in fact must meet a key requirement that the critical flash area of the component not be compromised. As stated above, a common misconception is: if it is covered, it is wildlife proof.
Installations of WPD covers on a range of components and equipment.
But this is not necessarily true since electric field can extend out beyond the physical limits of the WPD cover between seams and around ends of the material. An animal perched or sitting on a grounded mounting bolt that encroaches this critical flash area will cause a power frequency arc and flashover. The creature does not have to actually come into contact with the HV side – only move sufficiently close to it while at earth potential.
Based on the above, the optimum design for a cover type WPD is one that does not permit any encroachment into the critical flash area. The only way to ensure this in most cases is to use sufficiently large covers, making the installation simple and effective if not necessarily always aesthetically pleasing. ď ¸
Photos: INMR Š
Another possible oversight by users and manufacturers of this type of WPD has to do with leads. If the conductor must pass into the area protected by such devices, it too must be covered and protected for full voltage. Again, just because a lead is covered does not necessarily mean it is insulated for full voltage since the critical flash area extends beyond the insulation of the wires. It is therefore always advantageous, from a WPD perspective, for leads to enter and exit at the top of the cover. If this is not possible, other means may need to be employed to account for potential lead mismanagement.
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