WILLMAR -- A squirrel shorted out a three-phase capacitor bank located in the 1000 block of Willmar Avenue Southwest on Aug. 4. The event led to a power outage that lasted from 39 to 46 minutes in the southwest part of Willmar.
A report on the outage was presented to the Willmar Municipal Utilities Commission on Monday by Utilities General Manager Bruce Gomm and Jeff Kimpling, manager of electric services.
In an interview, Gomm said the squirrel climbed onto a capacitor. A capacitor is a piece of equipment that controls voltage. The squirrel caused "a fairly large arc'' that resulted in a chain reaction leading to the outage.
At the same time, two breakers at the southwest substation tripped, which caused the substation to go off-line. Gomm said the closest breaker to the fault opened to allow the fault to clear and then close.
But the next breaker upstream, which is a heavier duty breaker, also saw the fault and opened, but did not close right away on its own. When a breaker opens, the power is shut off, Gomm explained.
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As a result, Kimpling suggested the utilities hire a consultant to perform a relay coordination study.
A relay decides when and how fast to open a breaker, Gomm explained. Relays are supposed to be coordinated on the system so that only the closest breaker opens for the fault to minimize the amount of outage.
"But we've had a fair amount of growth in Willmar and we've added substations, and it appears as a result of growth that some of the relays aren't coordinated as well they could be,'' said Gomm.
The outage caused a power outage at the Jennie-O Turkey Store plant on Willmar Avenue Southwest. Utilities Commission member Jim Schammel, who manages the Willmar Avenue plant, said the outage resulted in $30,000 to $40,000 in damage to some electrical equipment. Schammel described the problem at the plant as unusual.
Gomm said all electrical industrial-type equipment in general is designed to be turned off and on without any negative effects. Gomm said the cause of the problem at Jennie-O is being investigated by the utilities and Jennie-O.
"We don't quite understand what all happened there, so his engineers are working with our engineers to see if we can figure out what's going on,'' said Gomm.
Attempts are being made to reduce outages caused by squirrels by burying as many overhead power lines as possible and by trimming tree branches, which can also cause outages, according to Kimpling and Gomm.
