ST. THOMAS — A problem with one of the generating units at the Harley Power Plant on St. Thomas caused more than 9,000 customers to lose power Wednesday afternoon.
The outage began at around 2:10 p.m. and all feeders were restored less than an hour later.
The outage included feeders 6A, 7A, 8B, and 9C, and approximately 9,368 customers were affected, according to WAPA.
“The outage was caused by underfrequency, which tripped Unit 27. Unit 23 was started to restore power to all feeders within the hour,” WAPA spokeswoman Shanell Petersen said in an email, in response to questions from The Daily News.
Unit 23 is the largest generating unit at the St. Thomas plant, and is a 39-megawatt GE generator owned by WAPA that first came into service in 2004. The aging unit has been kept on standby while WAPA acquires newer, smaller units.
The plant typically runs a configuration of smaller Wartsila generating units in tandem with 24-megawatt Unit 27, a newer, more efficient generator, but Unit 23 is still occasionally called into service in emergencies.
In response to a follow-up question, Petersen clarified that “underfrequency happens as result of not having enough load to supply all feeders with power. Once Unit 27 tripped, the system experienced underfrequency causing outages for the feeders recently impacted. The loss of generation from Unit 27 is still being investigated.”
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