Yukon Energy has taken its first guess as to what caused Thanksgiving Monday’s “mystery” outage.
A governor in Whitehorse hydro station’s third generator may be the culprit, said the corporation’s vice-president David McDonald.
Representatives of a company that provides governors are in town this week to figure out what happened to unit four, which caused Thanksgiving Sunday’s blackout.
They might also get to the bottom of the following day’s grid-wide outage.
“It’s the same sort of idea as unit number four,” said McDonald.
“The governor controls the output of the generator. If the governor is not working properly, the generator can either dump load or it can try to take too much load,” he said.
If the power coming out of the generator isn’t under control, the grid becomes sensitive to power fluctuations.
“It becomes unstable and then it would trip off,” he said.
It may have been a case of too much power, too fast.
There is more certainty about Sunday’s outage. Last week, Yukon Energy said a stuck valve in unit four caused it.
Now, it may have had more to do with the unit’s governor.
“At the time that (unit four) was operating, it had a significant proportion of the load,” said McDonald.
“What happens is that if the generator goes out of control, a big chunk of load has to be taken off and sometimes that can shake the system electrically — hard enough that it will take the whole system down.”
The system that keeps power fluxes from cascading into the rest of the grid failed to act quickly enough.
“A large portion of load went off, but the load shedding system wasn’t sufficient to get load off before the system went down overall,” he said.
Yukon Energy had to look back at all the records and alarms from Thanksgiving Monday before getting on the trail of the faulty governor.
But the Crown-owned corporation is still wary of fully endorsing the theory.
“That’s a bit of conjecture, but we think that that’s what happened,” said McDonald.
No one is ruling out other possible causes.
“I can’t say at this point that it’s a stuck valve, but we believe that it is the governor system,” said McDonald.
“But it could be stuck valve.”
The visiting governor experts will be in town as long as it takes to solve the issue, he said.
“They’re here so we can get the governors back operating in the short term, and so we can stop using diesel,” he said. They will help Yukon Energy locate the exact problem with the governor systems and Yukon Energy will then repair them.
The experts will also help with long-term plans to fix the persistent governor problems, said McDonald.
Both generators are offline during this week’s inspections.
Unit four is Yukon Energy’s most powerful hydro generator, and can produce 20 gigawatts. Unit three is the second-most powerful at the Whitehorse hydro station with a capacity for 8.4 gigawatts.
Whitehorse’s two remaining hydro generators produce 5.8 gigawatts.
The lemon generators have compromised Yukon Energy’s ability to produce power.
Secondary power sales were suspended earlier than normal this year, said McDonald. Once the generators are up and running again, secondary sales customers should be possible again.
However, once it gets colder, that privilege will be suspended, said McDonald.
Diesel generators are running at the Whitehorse power station to compensate for the failed generators.
The problems come at a busy time.
Yukon Energy plans to hook Sherwood Copper’s Minto mine up to the grid next week.
“We’ve still got some delivery equipment issues we’re trying to work out, but we expect that (the connection) is either going to be on the 30th or the 31st,” said McDonald.
Yukon Energy is currently running tests on the Minto mine connection, he said.
The utility is making sure power on both ends of the connection will flow at the same frequency and that the co-ordination in the relaying works well.
“(The tests) will not affect the grid. There are tests that you normally go through when you energize new equipment,” he said.
“We’re in the process of completing some of the installation and doing some of that commissioning testing now,” said McDonald.