Among the most vulnerable links in any power network are the points of interaction between live equipment and wildlife – from birds to scavenging carnivores. Taken together, these creatures present a constant threat to the safe operation of network assets. There are plenty of anecdotes of squirrels or feral cats being electrocuted and in the process blacking out entire neighborhoods while also damaging or destroying breakers and transformers. In the case of bushings, for example, shock waves from a wildlife-induced flashover can blow their porcelain housings into shrapnel that threatens safety and impacts nearby equipment.
The global economy is said to suffer huge losses each year due to sudden power disruptions and data suggests that as much as 12 percent of these are due to wildlife. If outages classified as ‘source unknown’ are factored in, most of which are thought to involve wildlife, the annual impact is even greater. Moreover, this risk is only growing given the focus these days on lowering costs, saving space and making electrical infrastructure less visible through compaction – in the process also reducing the distances that need to be breached to create faults.
Given the losses from outages triggered by wildlife, one might expect that the majority of installations from 5 kV to 38 kV, where clearances are most at threat, would be equipped with wildlife protection. Yet industry sources estimate the incidence of their application is still less than 20 percent. Many vulnerable substations remain ‘accidents only waiting to happen’. This article showcases one substation in Western Canada that has suffered a history of wildlife problems and which was equipped with protective covers and other wildlife deterrents intended to resolve this problem.
Overview of Wildlife Mitigation Devices
A number of factors are driving growing interest in applying wildlife protective devices at vulnerable substations. One is the universal goal of maintaining high system reliability. Another relates to the consequences of animal interaction with energized structures, which are not just power interruptions but also potentially costly damage to expensive assets. It has been estimated that such risk at substations could be reduced by 80 per cent through selective application of welldesigned wildlife protection products.
Yet another factor behind renewed interest in wildlife mitigation products relates to the potential for fines and penalties should protected species be electrocuted during phase-to-phase or phase-to-ground contact. Raptors typically have wingspans that place them at elevated risk of being involved in contact with energized equipment. This can become a problem at substations where clearances are determined by required flashover performance and not by the wingspans of local birds. In the western United States, for example, a large electric utility acknowledged responsibility in killing endangered eagles due to accidental electrocution. The utility was ordered to invest heavily in system upgrades intended to protect these birds.
Wildlife protection devices now being offered have different designs and are made from a variety of polymeric materials. One of the keys to performance is good fit since power arcs travel through air and the gap between the creature and the live fitting is critical. Any crack or seam in a protective covering could allow a power arc through and the higher the voltage, the greater this risk. Wildlife behavior also requires good fit to achieve best long-term results. This is because bird nesting at substations attracts cats, snakes and other predators that can dislodge loose-fitting covers as they push to the nest. They get electrocuted and the result is a costly outage.
Materials themselves are also important. All animal protection products start with a problem that must be addressed. But users need to be certain that whatever is being applied does not cause more problems than it resolves. For example, materials used must be fire-resistant and one of the goals behind IEEE guidelines for their application has been to assure that wildlife protection devices do not create new problems over the long-term.
One of the considerations when it comes to composition of materials used in these products is suitability to an outdoor environment of electric field and persistent high UV. Materials must be inert and resistant to tracking and erosion as they will face the same stresses as insulators, including dry band formation that can leave carbonized dots on their surface. Users are therefore advised to look at the tracking and erosion performance as well as UV test data for any wildlife protection device they consider installing. This is the only way to be sure these products will survive for years in a potentially hostile service environment. It is also essential to ensure that whatever latches attach the devices to the equipment they protect must not deteriorate over the years. If that happens, the devices can break off or shift under wind, exposing the live ends of equipment to contact by wildlife.