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ASPA acting director explains in detail what caused recent island-wide power outage

The ASPA Operations building in Tafuna
reporters@samoanews.com

Pago Pago, AMERICAN SAMOA — American Samoa Power Authority acting executive director, Wallon Young provided to Samoa News an ASPA report on what caused the power outage just after 9a.m., Monday.

The outage caused concerns among businesses, which were already busy with closing out books for 2019, and preparing for 2020. While the outage lasted about 10 to 15 minutes in some areas, it was longer in other areas.

Early Monday, the National Weather Service office in Tafuna had already put out a weather bulletin predicting strong winds with higher gusts.  During the power outage, ASPA provided updates on its Facebook page as well as on two local radio stations.

This is the entire power outage report detailed as provided by Young.

POWER OUTAGE

The American Samoa Power Authority sincerely apologizes for the island wide power outage that occurred around 9:05am on Monday morning.

Strong wind gusts caused power line conductors to come in contact with each other on at least one Tafuna feeder. This occurrence is referred to in the industry as "conductor clashing" and occurs on lines with incorrect tensioning — which can happen during  installation or over time. Conductor clashing can also be aided by flying tree branches or wind borne debris.

During conductor clashing, the feeder protection relay should trip the affected feeder — before any loss of generation.

This didn't happen on Monday morning because the temporary outdoor gen-sets at the Tafuna plant are unable to withstand feeder  short circuits long enough to stay on-line. These 1.5 MW gen-sets are inherently less "stiff " than the larger 3.5MW diesels at the Satala plant and the new 3.0 MW gen-sets currently under installation at Tafuna.

Conductor clashing on Monday morning caused the temporary gen-sets in operation at the Tafuna plant to trip and shut down. 

This resulted in the instant transfer of all Tafuna feeder loads to five GE gen-sets, that were on-line at the Satala plant at the time.  The Satala gen-sets ran 30% overloaded for a short time before shutting down automatically; leaving the island without power.

Technicians lowered protection relay short-circuit settings on all Tafuna Feeders on Monday afternoon — to allow the feeders to trip before any generation.

This was done to prevent a recurrence of Monday morning's outage, but it may increase nuisance tripping of the same Feeders.

RESTORATION

Operators started up both plants independently and began restoring power as soon as gen-sets were put on-line.

All five Feeders at Satala plant were restored within 38 minutes of the plant outage.

Feeder -8 (from Satala plant to  LBJ Hospital) was energized first at 9:25am.

The six Feeders at the Tafuna plant had to be divided into sections before energizing; this delayed the restoration time but was necessary to prevent the smaller Tafuna gen-sets from tripping out during feeder energizing.

The installation of three new 3.0 MW gen-sets is ongoing inside the Tafuna plant and commissioning is expected to begin in late January 2020.

ASPA is also planning to purchase two additional 3.5MW GE generators — also for installation at Tafuna plant.

The GE ge-sets are the same make and model as the diesels at Satala. When installed, the security of supply for the western half of Tutuila will be significantly improved.