Bringing Back Power a Slow, Tricky Process

Electricity in Demand

Inability to store electricity part of complex challenge Rolling blackouts likely to persist over weekend. When electrical power fails as it did Thursday afternoon across a large swath of Ontario and the northeastern United States, it can take days to restore and large cities, like Toronto, are usually among the last to regain service.

"We're now expecting it to take until Monday (to get power fully restored in the city)," said Karen Evans, a spokesperson for Toronto Hydro, the local utility that supplies 655,000 customers in Canada's largest and most demanding power market.

By late yesterday afternoon, the city had regained between 80 and 90 per cent of normal service, but isolated pockets remained in the dark, and rolling blackouts meant some areas that had electricity lost it for up to two hours.

The city began receiving limited emergency supplies of electricity on Thursday night around 10 p.m. for use by essential services such as hospitals, police, fire and ambulance stations, and water treatment plants, she said.

Homes and businesses connected to lines serving essential services also got service just because they happened to be on the route, Evans said. But service was fleeting in cases as some areas that initially got power later lost it, she said. "As people woke up (yesterday) morning and started turning on their lights, more power was demanded. We couldn't meet the demand so we had outages," said Evans.

In other cases, Toronto was forced to give up supply to meet demand in other parts of the province, another Toronto Hydro spokesperson, Blair Peberdy, explained late yesterday.

Rolling blackouts, as they're called, are expected to persist over the weekend as the Independent Electricity Market Operator, which manages the grid across the province, continues to adjust the supply to meet demand. The blackouts shouldn't last more than about two hours, Peberdy said.

Areas considered essential are less likely to get hit, Peberdy said. They include hospitals and other emergency services such as fire, police and ambulance stations, followed by critical municipal services, such as water pumping stations, then the Toronto Transit Commission, and finally major office towers and shopping centres. Downtown is given priority.

But Toronto Hydro is just one piece of the puzzle. When it comes to restoring power, a huge part of the challenge comes from the nature of electricity itself, experts said.

Think of electricity as a commodity that is manufactured, much like steel or lumber. But unlike other commodities, electricity can't be stored. It's produced at the very instant when it's needed. The lines that transmit power across the province serve as a dedicated point-to-point delivery system. Demand, or load, must be perfectly balanced with supply, or generation, or there's trouble — quick.

Most electrical systems operate on alternating current, which must be maintained at a constant speed of 60 Hertz, or 60 cycles per second. If demand exceeds supply it's like flushing a toilet while taking a shower — the flow of electricity slows. If supply exceeds demand, the flow speeds up.

Few electrical appliances can tolerate even small variations, leading to fried computers, fridges and power generating equipment. That's why most transmission systems are designed to protect electrical equipment by disconnecting generators from the grid when demand and supply get too far apart, said Tom Adams, executive director of Energy Probe.

"If they don't, there will be damage to the system and they won't be able to bring it back even in 24 or 36 hours," said David Drinkwater, energy consultant and former chief economist at Ontario Hydro.

In fact, an imbalance in the system is what caused Thursday night's blackout in the first place, experts agree, though no one can agree on where or how the upset began. All that's certain is that once the problem started it "cascaded" through the vast interconnected transmission systems that serve most of Ontario and the northeastern U.S., knocking out service to some 50 million people.

Once a massive failure has occurred, getting power back up from a "black start" is a tricky business, experts said.

First, Ontario has to be isolated from the other states and provinces that share the northeastern grid. Then specific communities are isolated from the rest of the province because power must be restored gradually to keep supply and demand in balance.

It starts with the handful of generating plants that have their own backup power. The rest join the grid after power begins humming along the transmission lines. The last to come on line are the nuclear generating stations since restarting them is a technologically trickier process. Ontario's nuclear stations account for up to 25 per cent of the province's supply

Initially, power is added in very small increments, as little as 10 megawatts every 10 minutes, a pace Adams called "glacial" for a system that was running 24,000 megawatts when it shut down.

As supply is increased, it must be matched by demand. At first, that might mean a single row of streetlights is added, then a neighbourhood, then a small community. There's little room for error and lots of potential for setbacks, experts said.

"I would compare it to being parked beside the 401 and having to go from a dead stop to full highway speed. You've got very little tolerance depending on whose fenders you want to bounce off," said Drinkwater.

Toronto is one of the last to get service because it is so large, said Toronto Hydro's Evans.

"We don't have priority because of the balancing issues. When you only have so much power available, you tend to target the areas of lower demand because excess demand is what causes failure," Evans said.

The supply of electricity in Ontario involves a number of players, including Ontario Power Generation, which runs most of the generating plants, and Hydro One, which operates most of the transmission lines that run between cities.

Overseeing it all is the Independent Electricity Market Operator, commonly called the IMO, which acts like a broker or middleman. It doesn't own any facilities but is responsible for matching supply with demand.

The non-profit organization decides when and how much power each part of the province, including Toronto, will receive. In an emergency, supply is distributed based on need, said Toronto Hydro's Evans. Carefully worked-out protocols determine who's first in line, Evans said. The IMO has so far refused to make this information public.

However, when Toronto Hydro officials realized Thursday night that the city was too far down the priority list to maintain its essential services, it appealed to the IMO for help.

"The IMO recognized we have essential services in the city, so we got power earlier than we expected," Evans said.

by Dana Flavelle and Madhavi Acharya-Tom Yew
Energy Probe