Tuesday, June 29, 2010

Havoc Wreaking Obese Raccoons


Last week, an alleged 40lb raccoon made headlines when he caused a major outage in the Medical District. The major hospitals affected had back up generators and were fine. However, the Commercial Appeal's generator wasn't strong enough to run its printing presses, so the Friday paper didn't go out until mid day. That sure got people's attention!

Naturally we've had some questions about how a rodent could cause so many problems. As you can see from our masthead, we have several animal friends who like to make their homes in our substations, play on our electrical wires, and occasionally wreak havoc.

So here's what happened. A giant raccoon was scurrying along on the substation structure. When he (allegedly a "he") decided to climb across a switch that was ~30 ft off of the ground, he became an unwitting conductor for a few milliseconds. Some times (most times) the protective service equipment breaks (opens) the affected circuit and the offending bridge falls away and the circuit can be closed in again. In this case, a lightning-like spark formed over and through the raccoon and destroyed portions of the switch which had to be replaced. This is what caused the long outage. It was a really unusual situation--you might even say it was the perfect storm because it was a critical switch at this particular station and one of the last ones you would think an obese raccoon could get across!

As far as animal mitigation goes, we have a systematic, economical plan in place. We start with the big ticket items, like transformers and breakers, which also add up to long outages. Much like chess, we protect the king and queen first, but we have to choose which of the "back" pieces to protect. (Switches might be considered rooks or knights.) And well, the pawns are often on their own. (i.e. The station class insulators - there are so many of them and they are typically much shorter than a raptor, squirrel or raccoon.)



Breaker with "Big Red Covers"


Before we started our Animal Mitigation Program, we looked at historical records and chose the stations that had the most animal outages. We have stored animal mitigation stock on hand and the field workers cover equipment that is put back into service because animals think alike and will likely use the same path to shelter or food.

Basically, we try to increase the distance between high and low voltage typically around insulators and bushings so that an animal cannot initiate an arc "over" the insulator. All of the possibilities are considered, but economics play heavily into the extent of the implementation. The animal mitigation components are not cheap because they have to have huge insulation properties and have to survive being in the elements for decades without degradation.


Switches with "Clear Polycarbonate Bushing Barriers"

To read more about our efforts, click here.

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