The complexity of switching lights back on
Globe and Mail - August 20, 2003
Ontario began to emerge from the dark within minutes of the blackout.
Not all the province's hydroelectric units were disabled, which is why places such as Niagara Falls were unaffected, and within minutes they were joined by a variety of hydro units across the river-rich northwest.
By 5:35 p.m., just one hour and 24 minutes after the province-wide transmission system went down last Thursday, one unit of the coal-burning station at Thunder Bay with a capacity of 150 megawatts was pumping out electricity to generating stations across the province that needed power to kick-start themselves.
Ontario was getting back on its feet.
Although, as we have discovered since, it can take days to get back to normal.
At the same time, about a dozen senior Ontario Power Generation staff members converged at an emergency centre at the company's headquarters on University Avenue in downtown Toronto.
A similar group met at a parallel backup centre in Durham Region east of Toronto.
Both groups had secure, open telephone lines to every one of OPG's 77 generating stations and were connected as well to the Independent Electricity Market Operator, Hydro One and the Ontario government's operations centre on Grosvenor Street.
Satellite phones were available if the land lines and cellphones went down.
When the blackout occurred, station operators across the province knew there was massive trouble, and each of them had moved quickly to assess the local situation and check for damage to their equipment.
By 6 p.m., however, each site had full support from the Toronto emergency team, which was staring at banks of computers that showed virtually no electricity generation happening in a province that on such a hot afternoon would normally have been pumping out about 23,000 megawatts.
It was essential that OPG get back on its feet quickly.
The Crown agency, one of the successor companies of the old Ontario Hydro, supplies about 75 per cent of the 155 billion kilowatt-hours of electricity that the province uses annually.
The giant Bruce nuclear station in Kincardine, which has a capacity of 3,160 megawatts and is operated by a private company, and a variety of other non-utility generators provide the rest.
OPG worked closely with the IMO to get electricity moving again. It wasn't simply a matter of turning on the switches and letting it flow, however.
Electricity is a unique commodity in that supply must always be matched by demand and surplus cannot be stored. The task of the system's operators was to ensure that the transmission grid and resulting demand for electricity were expanded in tandem with generation.
Rebooting hydroelectric stations, some of which produce less than 10 megawatts of electricity, was the simplest task. Restarting stations that burn fossil fuels -- coal, oil or natural gas -- is a little more complicated, but nothing compares to the complexity and drama of dealing with nuclear plants.
When the electricity grid failed, OPG had seven nuclear units operating: four at Darlington and three at Pickering B. Two other units, one at Pickering A and another at B, were just hours away from being hooked in.
The loss of the grid triggered an automatic response at all stations that removed them from the grid in milliseconds. Each unit responded somewhat differently, however. Follow-up decisions were made on site by operators who had undergone simulations of such an event, not by the emergency team.
At Darlington, which has a capacity of generating more than 3,500 MW, Unit 3 was stabilized at 60 per cent reactor power after the senior operator on duty determined it was safe to operate. Once the grid was restored, the IMO instructed the unit to return and it came on line at 10 p.m., six hours after the blackout began. It reached full power of about 840 MW the next day about 4 p.m.
At Unit 4, the operator was unable to monitor certain systems and acted in accordance with the operating practices drilled into staff to bring the unit down to the point where it was producing no steam and the turbines that drive the generator were inactive. The unit was reconnected on Monday and restored to full power yesterday.
At Units 1 and 2, managers similarly had trouble verifying that the systems in use at all four units -- those dealing with standby generators and water pumps, for example -- were working properly. They, too, were placed in a zero power state after being at 60 per cent power.
Unit 2 was reconnected to the grid at 30 per cent power on Sunday and has since been ramped up to full power. Unit 1 came on at 30 per cent power on Monday and was expected to reach full power yesterday.
The design at Pickering B, which is about 15 years older than Darlington, is different because units can operate at the standby 60 per cent capacity for only an hour. This is because, unlike Darlington, steam normally used to drive turbines when the grid is operating is not recycled but is vented into the air. Eventually the units run out of the demineralized water they need.
Unit 8 was placed in this position automatically but was reduced to 2 per cent because of low water levels.
At this point, rods that stop fission were inserted into the reactor and it was placed in what OPG calls "guaranteed shutdown state." Because it takes approximately four days to restart from this condition, Unit 8 is not scheduled to be reconnected to the grid until tomorrow.
Units 5 and 6 were shut down automatically when voltage fluctuations were detected on Thursday. Shutdown systems involving rods and the chemical gadolinium were inserted into the reactor to bring it to guaranteed shutdown state.
Unit 5 is scheduled to be reconnected on Saturday and Unit 6 the next day.
Unit 7, which was taken out of service for maintenance last February, wasn't connected to the grid when it failed but was operating at low power in preparation for its return. It was placed in guaranteed shutdown but is scheduled to be reconnected on Aug. 26 and eventually to provide 500 megawatts that wasn't there last week.
Unit 4, which is in the troubled Pickering A station, last contributed electricity in 1996 but was operating at 12 per cent power in preparation for imminent reconnection when the grid failed. It was put into guaranteed shutdown but is scheduled to be reconnected today and eventually produce 500 megawatts.