Relay system prevents massive outage

Manby Station Relay Protection isolated a 920 MW loss on Toronto's power grid, tripping breakers and safeguarding transformers, preventing a cascading failure. IESO and Hydro One contained the outage, avoiding a province-wide blackout like 2003.

When a burst of fire killed a breaker at the Manby Transformer Station in Etobicoke, the lights flickered across the province.

In a flash, the station, a key electricity transmission path for Toronto, lost 920 megawatts — enough to plunge a million homes into darkness, a power expert says.

“It could have daisy-chained throughout the whole northeast, leading to another blackout entirely,” said Frank Finnie, a power consultant with Missouri-based Power Generation Experts.

The station’s relay system disconnected the troubled site from the rest of the grid, isolating the problem to about 250,000 homes and quelling the ripple effect that had disastrous effects in the 2003 blackout when a local Ohio outage led to an international catastrophe that lasted several days.

“It can drag down the rest of the grid. If you lost 250,000 homes after losing 900 megawatts, they stopped it in half the time at least. It should have affected a million people,” Finnie said.

Breakers, transformers and power lines fail, be it from bad weather, a seismic event, capacitor failure in substations, or plain old age. However, utilities are supposed to have relay protection systems in place to nip the problem in the bud.

When the breaker at Manby caught fire, an alarm signal relayed the problem and disconnected that disabled mechanism from the rest of the power system.

“It means it’s contained as a local baby blackout event,” said Alexandra Campbell, spokeswoman for Independent Electricity System Operator, responsible for the day-to-day operations of Ontario’s electrical system.

“When the power went out, it was big enough that there was sort of a blip on the whole power system in Ontario,” she said. “Probably most of the province would have, as Ontario residents did during prior outages, seen that flicker.”

It did what the Ohio company FirstEnergy Corp. failed to do in the summer of 2003 when its gaffe turned out the lights for 50 million people.

In that case, the company’s information technology department knew of the problem and was trying to correct it. However, it never alerted the operators routing power through the wires.

As demand grew in the summer heat, the transmission lines began failing one after another.

It’s still unclear what caused the blaze.

In its 2010 shareholders’ report, Hydro One said the Manby station’s circuit breakers are nearing the end of their life and will be replaced by 2013.

Hydro One’s spokesperson said the faulty breaker had been inspected in 2008, adding that the cause of the fire was still under investigation, though some pointed to faulty sprinklers at the site.

Campbell, meanwhile, said the city wasn’t near its hydro capacity and the fire had nothing to do with a lack of available power. The heat wasn’t likely a factor, either, she added.

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