The power outage that interrupted last Sunday's Super Bowl was caused by a malfunction in an electrical relay device, according to Entergy New Orleans, the utility supporting the SuperDome in New Orleans.
"The device was specifically installed to protect the Mercedes-Benz Superdome equipment in the event of a cable failure between the switchgear and the stadium," Entergy said in a statement Friday. "While the relay functioned without issue during a number of high-profile events – including the New Orleans Bowl, the New Orleans Saints–Carolina Panthers game, and the Sugar Bowl – during Sunday’s game, the relay device triggered, signaling a switch to open when it should not have, causing the partial outage. This device has since been removed from service and new replacement equipment is being evaluated."
The power outage during the game was initially blamed on an unspecified "abnormality" in electrical load at the point where the feeder lines from Entergy enter the Superdome. In its initial report on Monday, Entergy and SuperDome operator SMG said the system to detect electrical supply problems operated properly.
"Shortly after the beginning of the second half, a piece of equipment that is designed to monitor electrical load sensed an abnormality in the system," the Monday statement said. "The fault-sensing equipment activated where the Superdome equipment intersects with Entergy's feed into the facility. Once the issue was detected, the sensing equipment operated as designed and opened a breaker, causing power to be partially cut to the Superdome in order to isolate the issue."
Entergy is now saying the relay device triggered when it should not have.
“While some further analysis remains, we believe we have identified and remedied the cause of the power outage and regret the interruption that occurred during what was a showcase event for the city and state,” said Charles Rice, president and chief executive officer of Entergy New Orleans.
In an analysis posted earlier this week, Amazon's James Hamilton examined several potential weaknesses in the SuperDome power infrastructuree, including swithgear.
"Given the Superdome just went through $336 million renovation, the switch gear may have been relatively new and, even if it wasn’t, it likely was almost certainly recently maintained and inspected," Hamilton wrote. "Where issues often arise are in configuration. Modern switch gear have an amazingly large number of parameters many of which interact with each other and, in total, can be difficult to fully understand. And, given the switch gear manufactures know little about the intended end-use application of each switchgear sold, they ship conservative default settings. Generally, the risk and potential negative impact of a false positive (breaker opens when it shouldn’t) is far less than a breaker that fails to open. Consequently conservative settings are common."