For two days, Hydro One and Hydro Ottawa worked on a plan to bypass a storm-ruined power station in western Ottawa, hoping to restore electricity to half the city at once in the early evening.

At about 8 p.m., they put it into action. In neighbourhoods across southwest Ottawa, the lights started to come on.

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Friday’s storm, which spawned two tornadoes and did massive damage in western Ottawa and in Gatineau, wrecked a major power substation near Merivale and Hunt Club roads. Major lines serving Kanata and south Nepean went dark.

The Merivale transmission station is where Hydro One’s electricity feeds into Hydro Ottawa’s system. It couldn’t be fixed quickly, Hydro One’s Jay Armitage said Sunday.

“We’re fairly certain, though we can’t confirm through photos or videos, that the tornado did touch down (on the Merivale station),” Armitage said. “It ripped the roof off of two buildings and the roof slammed into our infrastructure, the insulators, the wires.”

The target time to restore power moved later and later through Sunday — from noon to early afternoon and eventually to 7 p.m. — as workers kept running into new problems as they tried to bring a small but essential part of the damaged station back to life.

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After the storm, insulation, twisted wires and debris were everywhere. The Merivale station normally handles about 1,000 megawatts of electricity, half of what it takes to power Ottawa, and after Friday’s storm it was dead. Repairs will take weeks.

The Merivale station, tucked between a townhouse complex and railroad tracks near the intersection of Merivale and Hunt Club roads, is one of two major ones in the city. The other one is in the east, off Hawthorne Road near Hunt Club and Highway 417.

Those two stations are where Ottawa’s city electricity system connects to the provincial grid. A couple of big fat Hydro One power lines come in, numerous smaller Hydro Ottawa lines go out. They feed neighbourhood-level transformer stations all over the city, which feed transformers on poles (or in boxes, in some places), which feed individual buildings. Like water mains that divide into ever-smaller pipes until they reach a kitchen tap.

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In a storm, any of those wires can go down and since Friday, Ottawa has had power outages at all those levels. Central and northern Nepean, in particular, have power outages that aren’t because of the destruction at Merivale station.

“The problem is that the storm was so quick and so hard, it created so much havoc over the surface area,” said Joseph Muglia, Hydro Ottawa’s director of distribution operations. “First we have to assess the damage, before we can start fixing it … and then the first thing is to restore power to as many people, safely and efficiently, as quickly as we can. We have to co-ordinate what can get up running first.”

But what happened at the Merivale station is the really big deal.

A dozen medium-sized lines come out of Merivale. Some go east or northeast, to areas that can also draw electricity from the Hawthorne station in a pinch. But others are the only lines serving Kanata, Goulbourn, Rideau, south Nepean, south Gloucester and Osgoode. If those wires don’t have juice, whole regions of Ottawa go dark.

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“What the team has had to do is figure out a plan that primarily includes bypassing Merivale,” Armitage said. “So rerouting power through the different transmission stations to get power to the Hydro Ottawa substations through a different path.”

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The Merivale station runs close to its limits even when everything’s normal: in 2016, a Hydro One planning document figured that Merivale would be out of surplus capacity to handle ordinary equipment failures or other weird problems sometime in 2019, and unable to handle routine loads by 2024 or 2025. Hydro One and Hydro Ottawa have been working on plans to reinforce it either by replacing some of its transformers with higher-capacity ones or by building a third transmission station for south Nepean, where a lot of the increased demand is.

In the meantime, a lot of people in southwest Ottawa dangle out on the ends of just a handful of power lines.

(Even such important stations are built outdoors because burying them or enclosing them would be prohibitively expensive, Armitage said. Also, although they’re more vulnerable to the elements outside, they’re also easier to maintain than they would be underground or fully enclosed. A fire in an underground vault could be catastrophic.)

Much of Hydro One and Hydro Ottawa’s work since the storm has been making sure that lower-voltage wires and smaller substations could handle the loads when power was sent to them through back routes. Some power will have to flow through Merivale to make the plan work, too, so some of the equipment there had to be repaired quickly.

With the Merivale station not doing its usual job, the Hawthorne station and other smaller ones will have to work extra hard and the load will increase with every small line that gets reconnected in the days to come. Aside from hoping for good weather, Ottawans can reduce the risk of overloading equipment by restricting our electricity use.

“When you’re in this situation like this, where you lose a large station, you eat away at those redundancies. So if anything else should happen, should another storm happen, you will be more vulnerable,” Armitage said.

With files from Ken Warren