Blackout strikes part of Sisters

A new piece of equipment at the recently rebuilt Tollgate substation cut power to portions of the Sisters area starting at about 10:15 Sunday morning.

According to Don Lang, Chief Engineer with Central Electric Cooperative, a differential relay that is designed to detect problems within the substation itself "misoperated" and caused the failure.

Crews came from Plainview and Prineville to discover there was no fault in the substation, "so they were able to reset (the relay) and restore power," Lang said.

A majority of the affected customers were back on by 11:55.

"We had one other small tap between Washington and Hood Street and between Pine and Ash streets where power did not come back on until 12:45," Lang said. That delay was possibly caused by a bird or a squirrel shorting out a line and blowing a fuse.

On Monday morning CEC crews bypassed the differential relay that had misfired on Sunday. There are three similar relays in the Tollgate substation, Lang said.

A differential relay monitors both the current coming into the substation and the power flow going out. "As long as those are equal, it is fine," said Lang.

"But if you have problems, such as a squirrel on a piece of equipment, power flow coming in would not equal power flow going out. That is what the relay detects," he explained. When there such a difference, the relay cuts power.

The relay was new, since the Tollgate substation has just been rebuilt at a cost of about $300,000 following an explosion and fire that destroyed the substation in August, believed to have been caused by vandals with guns. It was brought back on line last Tuesday, October 31.

A representative of the company that sold the relay was scheduled to come over from Portland on Monday afternoon to analyze the failure.