Animal Guarding and Impact on Electric System Reliability

The most common example of an animal-caused service outage involves a squirrel and less frequently involves a bird, raccoon or snake. The figure nearby illustrates a typical example of a squirrel sitting on the top of a transformer  tank (which is grounded) and making contact with the primary lead above the bushing (or sometimes through the lighting arrester attached to the tank). Other less frequent examples involve these same animals on electric distribution lines and substations.

Small Impact on Reliability – Large Impact on Customer Satisfaction

In the case of the overhead distribution transformer, the outage is frequently “self-clearing” where the squirrel (or other animal) is shocked out of position or burned through. However, sometimes permanent damage results or a fuse is blown and a crew must be dispatched. In either case, these outages do not typically impact a large number of customers (perhaps only one to four if there is no secondary rack involved). Therefore, an all-encompassing programmatic approach to eliminate these types of animal-caused electric service outages is not generally cost-effective. Rather, each time a crew does respond to an animal-caused outage, they should deploy an animal guard, particularly since animals tend to repeat and share paths to and from food, water and shelter; and a device that experiences one animal-caused failure is likely to experience it again. Repeat failures at the same device means the same customers will be affected, potentially leading to an increase in customer complaints.

Leverage Tree Trimming to Address Lines and Substations

Animal-caused outages on primary lines and substations impact larger numbers of customers. Protecting (animal guarding) against these outages can be difficult and costly but they are necessary given their potential to negatively impact overall system reliability. Deployment of discs and enhanced fence protection are commonly warranted, but proper tree trimming (which is required as a general reliability measure) has proven to be one of the most effective ways to reduce animal-caused outages. Proper and timely tree trimming restricts animal ease of access to lines and to a lesser extent to substations.