Yellowknife plunged into darkness yesterday when the Northwest Territories’ Snare Lake hydroelectric power grid went down, cutting off power to the capital, Dettah and Behchoko at around 3:40 p.m.

It was -37 C at the time, and temperatures would reach nearly -40 C before power was completely restored around 7 p.m.

The Northwest Territories Power Corporation hasn't yet confirmed what caused the outage, but systems control manager Ken Dies says they suspect a fault in a power line about 140 kilometres north of Yellowknife. That brought down some of the larger hydro units which cascaded into a complete crash.

“It could be wind slapping lines together, it could be trees, it could be that frost just brought it down like they've had on the east coast,” Dies says. “Hopefully our line crew will discover what it was this morning.”

Dies says the company will also be investigating the delays in restoring power to the city.

During a power outage, the city relies on a backup diesel generating substation at Jackfish Lake. Some of the generators are supposed to start remotely but in some cases, that didn’t happen. Operators had to be called to fire them up.

Power came back up in parts of Yellowknife by 5:45 p.m. but went out again as the power corporation tried to bring all of the feeders out of the Jackfish Lake substation online. All but one of the 20 feeders was back up by about 6:45, but one of the large ones to Yellowknife continued to cause problems. Worried it would crash the grid again, the final circuit was splits into two feeders so it could be brought online gradually.

All customers had power restored by 6:52 p.m.

Dies says the power company has seen an increased load during the recent cold snap. Temperatures in Yellowknife have hovered below minus 30 for at least the last week. Dies says demand is slower over the holidays as offices and workplaces close down.

The power outage caused a lot of buzz online, as Yellowknifers turned to social media to find out what was going on.