“Protective Relay Failure” Allowed Local Blackout to Spread Islandwide, But Cause of Initial Blackout Not Explained


Guam -A localized blackout in Tamuning on November 3erd became an island wide black out according to a release from the Guam Power Authority because of “the failure of a system protective relay in the Tamuning substation” which “failed to isolate a line fault.”  But the cause of the initial “line fault” that resulted in a localized blackout that those “protective relays” failed to contain, is not explained, or even mentioned in the release.

The release summarizes a report on the causes of the blackout, without making mention of what caused two bursts of light along Ypao Road, one burst smaller than the other. The larger burst of light was seen across northern Guam, before the island-wide black-out occurred.

Friday’s release quotes Acting Assistant General Manager of Operations (AGMO) Melinda Camacho as saying: “The failure of the protective relay caused the line fault to persist affecting the Island Wide Power System (IWPS).”  Not mentioned in the release however, is any explanation of what caused “the line fault” in the first place.

The initial outage, that was not contained by those protective relays, occurred along Ypao Road in Tamuning shortly after 7 pm that Wednesday night.

What was the initial event that triggered the line fault that was not contained and led to the island-wide blackout?

The day after, at the scene, Assistant Manager of Transmission and Distribution, Simon Camacho, told PNC News that the large burst of light emanated from a power pole across the street from the Day’s Inn.

Read the original PNC story on the event by clicking here

Holding the damaged stretch of line in his hand he described how “arcing”  occurred between the power line itself,  and a lose buckle-clamp meant to hold the high voltage power line in place on the pole. The “arcing” acted like a blow torch, fueled by current in the the 34-thousand 500 volt power line. The arcing cut the power line in half,  the power line fell, slapping another power line below it,  causing the burst of light.

However that did not explain what caused that “arcing” between the loose buckle and the line. As Camacho explained it to PNC News, there must have been a sudden surge in current.

“Its 34-thousand volts, its a transmission line,” said Camacho. “But the big issue there is the amount of current that’s passing through the line at that time. So, I’m not sure exactly  what was the … at what part did this come in … but this is only one of the events that happened.”

The real question therefore is what caused that sudden surge in current that triggered the “arcing” between the power line and the loose buckle-clamp which cut through the power line, caused a huge flash of light, creating a localized blackout which became an island-wide blackout because those “protective relays” failed to contain it?

Camacho could not say for sure, at the time. But he told PNC News that day that 12 power poles north, next to the SDA Clinic, another flash had occured that same night of the “line fault,” and a Brown Tree Snake was found beneath that power pole. He did not know which event had occured first.

Camacho: “All I know is that we did find a dead snake and we found some burnt terminators, down at the end of the road, right before the housing.”

PNC: That could have put extra stress on this?

Camacho: “Yes.”

PNC: And subsequently triggered…?

Camacho: “Yea.”

PNC: So this might be a brown tree snake event?

Camacho: “Humm, I’m not sure.”

PNC: You can’t say so?

Camacho: “It could be coincidence. Yea. Coincidence.”

Read the GPA Release in its entirety below:


An island wide blackout on 3 November 2010 was primarily due to the failure of a system protective relay in the Tamuning Substation located behind the former Hakubotan Building.

The protective relay failed to isolate a line fault that occurred on a transmission line located along Ypao Road in Tamuning.

“The failure of the protective relay caused the line fault to persist affecting the Island Wide Power System (IWPS),” stated Melinda Camacho, P.E., Acting Assistant General Manager of Operations (AGMO), “This caused Cabras 3 &4 and MEC 8 & 9 baseload units to trip offline and protect their units, subsequently dropping approximately 112 MW (megawatts) of generation.”

The loss of 112MW of generation further led to other generation units isolating from the IWPS – both Tanguisson units tripped as a result of their protection systems. GPA dispatchers attempted to recover from the loss of the generation units by manually tripping breakers to stabilize system frequency. However, the loss of generation was too significant and Cabras Units 1 & 2 were eventually tripped to protect their units. It was at this time that the IWPS was plunged into a blackout.

“One of the recommendations of our internal investigation is to install backup protective relay systems. This will add another level of protection should another relay failure occur,” remarked Camacho, “Until such time backup relay protection systems can be installed, an SOP (standard operating procedure) has been instituted to manually trip breakers upon a relay failure alarm. This will further boost GPA system protection, which already employs a breaker failure scheme.”