Snakes inside substations is an age-old problem for electric utilities and, until recently, one that has been nearly impossible companies to solve.
Each year, bull snakes by the dozens were slithering into Western Farmers Electric Cooperative’s (WFEC) substations from April to July. During these months, birds were laying eggs in their nests on top of electrical equipment in the substations, and hungry snakes sneaked into the substations. While the reptiles could find their way up to the top of the equipment, they often got into trouble as they tried to crawl back down using a different route.
Bull snakes measure about 5 ft long, feature a speckled, goldish-black color, and go by the names “chicken snake” or “rat snake.” They are not venomous, but they’re skilled climbers, which makes them especially troublesome to have inside of an electric utility substation.
ften, these snakes would go phase-to-phase or phase-to-ground, knocking out the circuit recloser located on the outside of the bus. Then, when a fuse was blown, the entire substation went down, knocking out power for thousands of WFEC’s customers. High-side fuses often cost between $1,000 and $4,000, and one snake could inflict thousands of dollars worth of repair and replacement costs. In addition, WFEC lost income during the snake-caused power outages.
In one of the worst examples, one snake caused a $300,000 transformer to go out of service. The snake slithered up onto the transformer, went phase-to-ground on a bushing and caused a phase-to-ground fault, which blew into another phase. That phase then went into another phase, which sheared up all of the bushings on the transformer and eventually blew it up.
A snake went phase to ground on a recloser
A snake wrapped around the wire on the co-op’s homemade snake guard.
Tired of spending time and money to keep snakes out of the substation, the co-op experimented with different solutions. To this end, WFEC created an in-house snake guard out of an AC fence charger and rubber hosing. To build this guard, the co-op tied the rubber hosing to the tin around the bottom of reclosers, used a black tie to secure the wire on top of it to insulate it from the steel, then electrified the fence with the charger.
When a snake came around the side of the fence, it would get a mild shock and would then back out and curl up. In some cases, when the charger got a good ground on the snake, it would lock it up, eventually killing it. When this happened, it would ground out WFEC’s homemade snake guard. Subsequently, another snake might approach the same fence. This time, however, the snake could easily make its way undeterred into the substation.
To solve this problem, WFEC then installed two guards for an extra line of defense. One guard was close to the ground and another one was up higher.
Another problem with the original snake guards is that when it rained, it would ground out the snake guards. When the charge was down, the snakes would safely enter the substations, eat the bird eggs, and then sit for a day or two digesting them. Then when the AC fence charger began working again, the snakes would try to exit the substation unsuccessfully, creating yet another outage.
After unsuccessfully trying to make its own snake guard work, WFEC found a product from TransGard Systems and learned Oklahoma Gas & Electric was using the technology to protect its substations. WFEC visited the utility to learn how the technology worked and examine how well it was keeping snakes out of its substations.
Seeing the effectiveness of the TransGard systems, WFEC opted to invest in a few of the TransGard fences and specially designed snake panels. This electric fence, which has a 2,000 VDC charge, delivers a mild shock to snakes if they crawl up to the fence and try to get through the first layer. This shock often will be enough of a deterrent, but if the snakes are still determined to crawl up higher on the fence, they will incur a higher voltage, often knocking them down to the ground. The gate has a switch so that the workers can turn it off when they are working inside the substation. They also can enter the substation from an alternate gate that is not energized.
Five years ago, TransGard came to WFEC to install 250 ft of the fence, which is made of metal and PVC pipe. Overall, it took about 3 hours to finish the installation, hook it up, and get it energized and ready to act as a deterrent. The crew had to shovel gravel on to the footings to keep the fence from blowing away. In addition, they placed the guard at an angle so it wouldn’t lean over in strong wind
WFEC has installed Snake Guards at 33 of its substations and plans to install 10 more in the future. The length of the fence varies between 250 ft for the smaller substations to 450 of the larger substations. WFEC has 280 substations, and the co-op is installing the guards in all new substations and any new rebuilds.
Following the installation of the TransGard fencing, WFEC has not had a single snake enter its protected substations. By keeping snakes out of its substations, WFEC has been able to increase its power reliability, minimize power outages and protect its electrical equipment.
Billy Young ([email protected]) is a station specialist for Western Farmers Electric Cooperative.
Editor’s note: To see a video of how WFEC addressed its snake problem, visit http://youtu.be/r_nsp1jXrpA.
Western Farmers Electric Cooperative | www.wfec.com
TransGard Systems | transgardfence.com