Two unrelated events, separated by mere miles and minutes, affected two 115-kV transmission lines and four substations operated by Tacoma (Wash.) Power on Oct. 12.
“It was a bad day at Black Rock,” Tim Burtron, senior supervisor with Tacoma Power, told TransmissionHub Oct. 16.
Shortly before 4:00 p.m., fire broke out on a wooden pole that supports the transmission lines that feed a packaged gas production facility of industrial gas manufacturing company Praxair near the community of Fife, Wash., west of Tacoma.
“We have a tap off a loop transmission line that feeds two, 115-kV banks that Praxair owns,” Burtron said. That fire disrupted service to the company, caused the line to sag where it crosses busy Interstate 5, and affected the nearby Fife substation.
The cause of the fire was determined to be a phenomenon called “tracking.” Dust and dirt built up in the insulators during the recently ended 80-day dry spell, and when that dust became wet, it became resistive and caused a heat build-up that led to the fire, Tony Psaris, Tacoma Power construction and maintenance assistant manager said.
“We clean those insulators when Praxair has an outage … and it’s been over a year,” Psaris said, adding that frequent Northwest rains usually keep the insulators cleared of dirt between cleanings.
Less than an hour later, at about 4:40 p.m., a semi truck backed into guy wires supporting the 115-kV Northeast-Stoebehlah line, “snapped off some post insulators and brought the transmission line down,” Burtron said. That event also tripped three area substations out of service.
Service to the Praxair feeder line was restored just before 9:00 p.m., approximately five hours. The Northeast-Stoebehlah line was restored to service shortly before 10 p.m., slightly more than five hours, he said.
“For the type of damage, I believe the lines were restored fairly quickly,” Burtron said. “I think our crews did a very good job.”
Approximately 7,500 Tacoma Power customers were affected.