St. Thomas Blackout Due to Communication Issue

A loss of communication between key systems in the Water and Power Authority’s generating unit No. 23 was responsible for the unit’s tripping offline, the loss of another generating unit and, subsequently, the failure of all electrical feeders in the district, according to WAPA. Unit No. 23 is WAPA’s largest generating unit, often called its workhorse.

WAPA Acting Chief Executive Officer Julio Rhymer said Thursday plant personnel found No. 23’s exciter tripped “due to a loss of communication with the unit’s exciter control modules. This loss, in turn, activated the generator’s protection scheme resulting in the unit tripping offline,” he said.

“The loss of Unit 23 had a domino effect on the other generator online at the time, Unit 25,” he added.

The loss of the units occurred at 12:57 a.m. and plant personnel, the line department and system planning engineers began to troubleshoot the cause and effect of the electrical service interruption in the ensuing hours.

Due to the unique nature of unit No. 23’s failure, WAPA personnel had to take time ensuring that the root cause of the unit’s tripping had been identified prior to attempting its restoration, according to the utility. Thereafter, three smaller generating units – Nos. 14, 18 and 25 – were brought online and restoration of service was begun at 4:40 a.m.

“The plant also brought a fourth unit, unit 15, online in the event additional generation capacity was needed,” Rhymer said.

With power restored, WAPA rebooted various components within unit 23’s control modules and the unit was restored to service at around 10 a.m.

WAPA has already reached out to the unit’s original equipment manufacturer to provide additional technical assistance in improving the unit’s reliability until a scheduled major overhaul takes place in September. The unit must undergo a major overhaul before it is converted to burn tri-fuel: propane, natural gas and oil.

In the event of a major service interruption, regular updates are available on the WAPA website, its Facebook page, telephone Message Six option, via VI Alert and through the local news media, Rhymer said.

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