So, you call in a guy with a line gun.
“For the bulk of the work we’ve done for the last couple of years, we’ve used a helicopter,” Chris Marshall, spokesman for Burns and McDonnell Engineers, said. “But for this, where they only need to do a fairly small crossing, a helicopter is just too expensive.”
Burns and McDonnell is the contractor managing the Maine Power Reliability Program upgrades.
The line gun is a standard naval issue 45-70-caliber rifle-shaped tool, designed to fire a brass dart attached to a string across a gap of open water. Normally used to send lines between boats, it’s one of the handier devices for Central Maine Power line crews and their contractors.
“They make a utility kit, primarily for this purpose,” Josh Teel, project manager for Elecnor Hawkeye, said. “Our application is to use it to get our ropes across spans that we can’t take equipment through.”
Crews from Burns and McDonnell and Elecnor Hawkeye finished their Androscoggin River crossing in Lewiston-Auburn on Monday morning, attaching three conductor lines coming from Lewiston into Auburn just south of the Vietnam Veterans Memorial Bridge with the line gun’s help.
Monday’s project is the last part of the current phase of the Lewiston Loop, an offshoot of the Maine Power Reliability Program. It’s a $1.4 billion upgrade that erected 442 miles of transmission lines across 75 cities and towns.
The Lewiston Loop, a 115-kilovolt transmission line, will connect the Larrabee Road substation to a yet-to-be-built downtown substation on Middle Street, at the foot of the Great Falls on the river.
Now CMP contractors will move to downtown Lewiston, building the Middle Street substation and attaching it to the rest of CMP’s power line infrastructure. That work should start in April, according to Marshall.
Even with the gun, getting a power line across a river is a detailed process. The gun fires a 10-inch long dart, attached to a nylon string. A team on the other side — in this case, on the mid-river island below the Vietnam Veterans Memorial Bridge — collects the dart and uses the string to pull a stronger nylon rope across to them.
The team on the Auburn side then pulls the nylon rope back, attached to a much sturdier rope.That’s attached to the line infrastructure and used to pull a steel cable across the river to the island, up and over a set of existing 34.5-kilovolt lines that power Auburn.
That steel cable is used to pull the power conducting cable that will carry 115,000 volts through the system back to Auburn.
Then, the teams reset and start over again: Line gun, dart, string, rope, bigger rope, steel cable, conductor. Crews used the method to wire the last three of the 115 KV lines Monday.
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