Electrical service to customers in the St. Thomas-St. John district was restored late Sunday afternoon, after a district-wide electrical service interruption which occurred at 9:35 a.m., the Water and Power Authority announced Sunday evening.
At the time of the interruption, the three new Wartsila units were dispatched, providing a combined 21 megawatts of electricity to the grid, and Units 15 and 27 were also dispatched, WAPA reported in a news release. The apparent fault triggered protection schemes which shutdown the Wartsila units, and resulted in a cascading effect on the other two units, he added. The islands of St. Thomas, St. John, Hassel Island, and Water Island were affected by the service interruption.
“Initially, we are focused on confirming whether a suspected transformer fault at the point where generators connect to the transmission and distribution system is the cause of today’s service interruption,” said Clinton T. Hedrington, Jr. WAPA’s chief operating officer of electric systems.
Plant personnel worked to restore Units 15 and 27 to service.
“There is an extensive restart procedure that must be followed when the unit’s trip off-line with full load as they did today,” Hedrington explained. “At times, this involves hours-long procedures to properly restart the units and reconnect them to the electric grid.”
At 1:45 p.m., and with Unit 15 back on-line, plant personnel began restoration of service first to Feeder 5A, and then to a number of feeders including 8A, 9B, 7B 10B, 8B, and 7A. Later, with two additional generating units, Units 25 and 27, on-line, all remaining feeders were fully restored at 5:10 p.m.
“Our team of engineers will continue to evaluate the apparent fault which resulted in today’s service interruption,” Hedrington said.
Additionally, a line department crew was dispatched late Sunday afternoon to investigate the cause of an apparent isolated interruption on Feeder 9E, which serves a portion of St. John, WAPA reported. All customers on the feeder were restored at 6:35 p.m.