Residents in some areas of Tutuila experienced more than one power outage over the weekend.
On Friday night at about 12:30 am a lightning strike caused an outage which affected all three phases on one of the feeders or power supply lines at Satala close to the plant according to Chief of Power at the American Samoa Power Authority Wallon Young.
The outage was preceded by heavy rain and lightning.
Young explains that lighting strikes are essentially electrical conductors. When lighting strikes a power line – they easily cause flash-overs and short circuits between phases.
He says even if the lighting energy is rapidly discharged to ground by lightning arrestors – the flash over and resulting short circuit between phases often results in an outage.
The power chief says ASPA’s existing Satala plant is unable to sustain any close-in 3-phase fault without shutting down.
This is what occurred on both Saturday and Sunday and according to Young the evidence for this is the -under-voltage trips on the Satala gen-sets.
Young point out there is an inherent weakness in the existing Satala power system.
Due to the relatively small generators at Satala – the stiffness of the Satala grid is very low which he says is a typical problem with small system.
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During 3-phase faults (like the flash-over this past weekend or when lighting strikes and causes a flash-over on all 3- phases on overhead lines)- the Satala generators and grid voltage instantly dips below 20%.
This in turn causes the under-voltage protection on the Satala generators to activate – resulting in the shut down of all Caterpillar generator units.
In contrast, there are no under-voltage trips on ASPA’s larger Deutz generator sets at Tafuna.
Asked why it took a while for ASPA to restore power, Young responded, “This wasn’t a typical transient fault – where an affected feeder could be re-energized a minute or two after the fault.
The fault on Sunday was a permanent 3-phase fault that caused all six on-line generator sets at Satala plant to automatically shut down.”
He said the restoration of ASPA generators took 23 to 33 minutes.
ASPA’s power chief told KHJ News the outage duration was longer than normal – because standard operating procedures required duty operators to first inspect and record all alarms and shutdowns – so that a quick analysis could be carried out.
It took a little bit more work to collect data from all six containerized Caterpillar units at Satala plant – because these units are scattered over half acre of land at Satala.
After the analysis – the faulted equipment was isolated. All alarms and shutdowns were reset – before the generator sets could be restarted and feeders re-energized.
