Minnesota Power was investigating a series of momentary power outages in Cloquet and Duluth this month. On Monday, spokeswoman Kelley Eldien said the power company has received numerous calls about the “momentaries” that last for just seconds but can cause items such as computers to go down. There have been similar calls about outages in the East Hillside neighborhood of Duluth. The cause remained a mystery to crews earlier this week, Eldien said.

Power companies across the country have reported more “momentaries” as power grid equipment becomes more automatic and sophisticated in d...