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Fallen tree cause for Tuesday night power outage

Nearly 16,000 customers without power for about 1 1/2 hours

Posted: November 2, 2011 - 2:09pm

A fallen tree is to blame for the area-wide power outage that blanketed Juneau in darkness for about an hour and a half Tuesday night, according to a spokeswoman for Alaska Electric Light & Power Company.

Debbie Ferreira, AEL&P spokeswoman, said high winds blew the large tree over, and it came to rest on two main transmission lines and a distribution line on Channel Vista Drive at 8:13 p.m. The incident left 15,844 customers without power.

“It was definitely wind, the same as the other two outages earlier in the day,” Ferreira said, referencing two similar but separate instances around noon and 1 p.m. Tuesday that affected 6,377 customers. “It’s almost like those two lines were supporting the tree.”

Night crews scrambled to cut the tree out of the wires, while the emergency/after-hours office fielded 43 phone calls and took 23 messages during the duration of the 1-hour, 26-minute-long incident. The tree was out of the line by 9:15 p.m., and all hydropower was restored by 9:39 p.m., Ferreira said.

The tree actually did not damage any equipment, such as utility poles or wires, on Channel Vista Drive. She said anything that allows the electricity surging from the wires to find a path to ground, such as a tree in the line, causes a short circuit, or fault, in the flow of the current. That causes large circuit breakers to automatically open the line to prevent the flow of dangerous or destructive current, according to AEL&P power generation engineers.

The opening of the circuit breakers interrupts the flow to electricity beyond the fault. If it happens on the mainline from Snettisham, it results in an area-wide outage.

AEL&P did run its diesel generators for less than an hour, from about 8:47 to 9:35, to provide power to customers out the road and in Mendenhall Valley, Ferreira said. That will lead to only a “fraction of cents” increase on customer’s bills. The cost for momentary outages like Tuesday’s is already budgeted into customers normal cost of power adjustment, she said.

The cost of fuel at the time is one of the main factors that determines how much customers will be charged the use of the diesel units, which has the potential to energize all of Juneau when hydropower is cut off. Customer bills skyrocketed up 400 to 500 percent during a month-long power outage caused by avalanches in April of 2008.

In that case, about 50,000 gallons of diesel per day were burned to meet the community’s electrical demand, and electrical rates rose five to six times the normal rate.

The last area-wide outage that affected all 15,844 customers was in April of this year. It was caused by a failed transformer fuse in Douglas, and that outage lasted 1 hour and 50 minutes.

There have been about 60 brief power outages this year, according to the AEL&P website, most caused by trees, animals, cut-out failures or failed transformers. There were four area-wide and 81 total outages last year.

Most agencies in Juneau are well equipped to deal without its main hydropower source. Bartlett Regional Hospital, for instance, has a 1,000-kilowatt back-up diesel generator that automatically kicks in to provide power everywhere in the building, including surgical suites, birthing centers and all patient areas, except the administration wing and some offices.

By law that generator is required to have 72 hours worth of diesel on hand to power the entire hospital. BRH always keeps a week’s worth, said BRH media liaison Jim Strader.

Strader noted that generator instantly turned on Tuesday evening during the outage as it’s supposed to.

All of Juneau’s power is generated locally since it is not connected to a larger power grid. More than 98 percent of AEL&P’s power comes from the Snettisham Hydroelectric Project, and the rest is generated from the Lake Dorothy, Annex Creek, Salmon Creek, and Gold Creek Hydroelectric Projects.

Two main transmission lines — “a highway of electricity” as Ferreira describes them, since they carry 69,000 kilowatts each — run from Thane Road to Salmon Creek. Electricity runs through both of them at the same time so they share the load of the current, and there are two in case one goes out since they both run through the avalanche zone on Thane Road. Line 1 continues on from Salmon Creek to out the road.

Beneath both lines is a distribution wire with a much lower voltage frequency that distributes power to homes, other locations and feeders.

• Contact reporter Emily Russo Miller at 523-2263 or at emily.miller@juneauempire.com.

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