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Final checks being done on Northwest Transmission Line
INSPECTION teams are now going from tower to tower along the 344 kilometre length of BC Hydro's Northwest Transmission Line, methodically checking each one prior to the line being energized sometime next month.
The checks are part of the commissioning of the $736 million 287 kilovolt line, construction of which was officially completed June 7, says Jim Shepherd, the BC Hydro manager in charge of the project.
“They're looking at each of the 1,092 towers – the foundations, testing each of the bolts, the sag on the [conductor] line to see if it's correct,” said Shepherd.
And while the towers are being inspected, so to is the equipment at the BC Hydro's existing Skeena Substation south of Terrace, which connects the line to the provincial power grid, and the new one built where the line ends at Bob Quinn on Hwy37 North.
“There are 40 steps and 85 pieces of major equipment,” said Shepherd of substation work checks.
The Northwest Transmission Line also includes a fibre optic communications system that is also being checked to make sure it works, Shepherd added.
“We're doing all of this very, very carefully,” he said of the transmission line which is engineered for a life span of 70 years.
The actual energizing of the line, when ready, will be fairly low key, Shepherd continued.
“It won't be a switch. It's a button and a qualified BC Hydro technician will be the one pushing that button,” he said.
During construction, workers strung nearly 2,100 kilometres of electrical line, called conductor in the power line business.
That length accounts for three separate phases of two conductor line bundles each which span the transmission line's distance.
Shepherd said the total length was approximately the driving distance from Terrace to Regina, Saskatchewan.
The Northwest Transmission Line's two immediate customers are Calgary-based AltaGas, which will feed power it is selling to BC Hydro into the line from its three run of river hydro-electric projects along the Iskut River west of the Bob Quinn substation, and Imperial Metals which will take power to run its nearly-finished Red Chris copper mine located north of Bob Quinn.
Each company is responsible for its own connection lines to the Bob Quinn substation.
Shepherd expects the Forrest Kerr run of river project, the largest of the three belonging to AltaGas, to be the first user of the Northwest Transmission Line by beginning to feed power in next month.
“As you know, AltaGas is now commissioning Forrest Kerr and we expect that to happen in July,” Shepherd said.
The completion of the Red Chris mine and its taking of power from the Northwest Transmission Line will happen afterward.
First envisioned more than a decade ago with several starts and stops along the way, the Northwest Transmission Line was officially announced in the fall of 2009 with prime contractor Valard Construction and engineering company Burns & McDonnell being chosen in the fall of 2011 as the lead companies for the project.
Also in 2011 BC Hydro began signing benefits agreements with First Nations and the Nisga'a Nation along the transmission line route, setting out contracts for clearing right of way and other economic arrangements.
The line was originally scheduled to be in service at the end of May but a combination of terrain and weather during construction caused some delays.
Work was also shut down on the project in March when a worker fell from a man bucket suspended by a crane about 85 feet above the ground and was killed.
The shut down was not only in respect for the worker but also to check work practices.
“We wanted to make sure we were safe for our workers going forward,” said Shepherd.
Of the nearly 1,100 towers installed, a number of which were airlifted into place by a heavy lift helicopter, two collapsed.
Both were secured temporarily awaiting permanent installation at the time of their collapse, said Shepherd.
“The towers were in the same place and that turned out to be a very windy area,” he said.
The transmission line is engineered to withstand a 1-in-100 years storm with no major damage, a 1-in-50 years storm with no service interruption and a 1-in-2,475 years earthquake.
What this means is that if there was a worst storm condition in a 100-year period, there would be no major damage and that if there is a worst storm condition in a 50-year period, the line will work fine.
And if there was a worst earthquake in a 2,475 year period, there would be no major damage to the line.
If towers are in an avalanche zone, they must withstand a worst avalanche in a 100-year period and if towers are in a flood area, the must withstand the worst flood in a 200-year period.