Doug Simpson of the Alberta Electric System Operator says the last time six plants went down on the same day was in 2006.
He told an Alberta radio show on Tuesday that there was no way to predict so many separate failures in such a short time.
"There's no way to predict there's going to be forced outage" Simpson said. "These units run 24 hours (a day) and they're bound to have things like this go on."
The blackouts hit Edmonton, Calgary and Lethbridge on Monday and involved four separate power companies.
The system operator had earlier said the reason for the plants going down wasn't going to be released because the companies were concerned about competing on the open market.
Alberta NDP critic Dave Eggen suggested there's more to the blackouts than the system operator is letting on. Eggen suggested they highlight the failure of the Conservative government's market-based model for electricity.
“We must have a report on why those four plants were down ... or on whether there was any illegal manipulation of the system to jack up prices, or on why power companies can build a plant anywhere and we just have to build transmission to work with those plants,” Eggen said in a release.
“But we don’t need a report on whether this deregulation nightmare is working for Albertans, either in terms of reliability or in terms of affordability.”
Eggen said power prices Monday shot up to $1,000 a megawatt hour from $11 in a matter of hours. He predicted the extra cost is likely to be tacked on to customers' bills.
Alberta’s electricity system was deregulated in the mid-1990s and power prices have since reached record levels. The New Democrats have been demanding in recent months, including during last spring's election campaign, that the government return to a regulated system. Joe Anglin, the Wildrose Opposition's utilities critic, is demanding a public investigation into what happened Monday.
"Market manipulation occurs when generators deliberately turn off generation," he said. "Here you have six generators shutting off for six separate reasons. That isn't just unusual, that is so improbable you're in the range of winning the lottery kind of odds, so this is really suspect."
Simpson said no further blackouts were expected Tuesday.