The number four turbine at the Whitehorse Rapids Dam was shut down Monday morning because of a problem with its governor, causing brief power outages in Porter Creek and Riverdale.

Mike Sage, a system operator who oversees the sophisticated control centre overlooking the dam, said he had some warning from staff that there was an issue, providing him with some lead time to begin bringing backup generators online.

"You just don't flick on a switch,” Sage explained during a tour Monday of Yukon Energy's brain centre which resembles the bridge on the USS Enterprise.

Time – not a lot, but time nonetheless – is required to synchronize the generator with the system, to make sure it is operating at the same frequency and producing the same voltage, added control centre supervisor Guy Morgan.

Sage was in the middle of the firing up the backup hydro unit – and four diesel generators – and had reduced the load on number four by 25-30 per cent when the unit when down, causing breakers to trip at 9:32 a.m.

Morgan and Sage are quick to defend the recent installation of a new digital governor on the number four turbine – the newest and largest single hydro unit in the Yukon with the capacity to generate 20 megawatts – as a positive step forward for the Whitehorse-Aishihik-Faro (WAF) grid.

To some degree, however, Yukon Energy staff are still adapting to and tweaking the improvements, Morgan said.

He said because of the huge cost of hydro and diesel generators, they are fitted with sensitive safeguards that shut them down automatically and quickly at the first sign of trouble to avoid any damage.

It's Sage and the four system operators who staff the control centre in 12-hour shifts, 24-7, to watch over the WAF and Mayo-Dawson grids.

"The control centre operator is the first point of contact if anything goes wrong,” said Morgan. "When we lose generation, it's always a big balancing act here. You have to know what you lost and you have to know what you need to pick it up.”

Sage's work station is surrounded by a dozen or so large computer screens, showing him every little detail about the power being generated on both grids, in real time, second-by-second. He knows how much juice is being drawn by Riverdale residents at any given time, or in Porter Creek.

The Minto Mine was drawing 3.8 megawatts mid-afternoon Monday.

With the information before him yesterday morning, Sage began preparing to lose the 18 megawatts number four was putting out.

He dialed up the output from the Aishihik Dam's two 15-megawatt hydro generators, and fired up four diesels, and started up the third hydro unit, with its capacity to generate a maximum of 8.2 megawatts.

Riverdale was back on in three minutes, and Porter Creek five minutes later.

Number four was back in service at 4:20 p.m., though it was driven back up to capacity slowly.

Three of the four diesels were taken off-line as the morning demand dropped, though a fourth was kept running all day.

Morgan doesn't like to see the diesels burning fuel, because of the enormous cost, financially and environmentally.

For the eight hours the number seven diesel was online Monday, it was going through 700 litres of fuel an hour.

When Dawson was powered by diesel generation until the Mayo-Dawson line was completed in 2003, it cost $10,000 a day to supply the 1,800 or so residents.

The Mayo-Dawson line, Morgan said, may have had its struggles, but it's proving to be a solid investment.

One of the duties Sage and his colleagues are charged with, Morgan pointed out, is plotting the anticipated load on both grids, day-to-day, hour-to-hour, using data from historical consumption and forecast temperatures.

He said with that information, they're able to manipulate water levels in Schwatka and Aishihik lakes to ensure there's enough storage to meet demand with hydro.

It's usually the graveyard operator who starts at about 4 a.m. who sets up the required volume for the next day's demand, which usually peaks about 6 p.m. when everybody's home cooking supper, Sage explained.

"He is trying to do everything he can, not to run diesels,” Morgan said.

"It's an environmental thing for us, and it's a financial cost to us.

"We are trying to make money, we are trying to run a business."

He said there are different options available when the load on the WAF grid reaches near capacity at 55 megawatts, such as shutting off large consumers who buy excess hydro at a cut rate to use for heat, instead of burning oil.

Whitehorse General Hospital, for instance, is such a consumer.

Monday afternoon, Sage was maintaining generation on the WAF grid at 48.3 megawatts, with a little wiggle room to smooth over bumps in the system.

Morgan said as much as Yukon Energy staff – and the staff of Yukon Electrical Company Ltd. – are dedicated to supplying their customers, as much as they understand the importance of their job and the essential service they provide, some things are just beyond their control.

There are, to be sure, changing weather patterns, he said.

Morgan said in the 23 years he's been with the publicly owned corporation, he's never seen as many interruptions caused by lightning as he has in the last couple of years.

"A snow load last April brought down a line."

But with the proposal moving forward to tie the two grids together, and with the planned addition of a new seven-megawatt hydro unit at Aishihik, there'll be that much more flexibility to manage the system, Morgan said.