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Con Edison to examine lightning bolt-like arc flash at New York City substation

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Con Edison to examine lightning bolt-like arc flash at New York City substation

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New Yorkers jokingly dubbed the Dec. 27, 2018, electrical arc flash the "Astoria Borealis."
Source: Benjamin Passikoff

Contrary to social media speculation and initial news reports, neither extraterrestrials nor a transformer explosion at a Consolidated Edison Co. of New York Inc. substation was behind the pulsating blue glow that recently lit up New York City's nighttime skyline.

The utility originally issued a statement indicating that a brief electrical equipment fire at the substation caused the spectacular light display and a related "transmission dip." But it has since determined that an electricical fault at a Queens substation produced a sustained lightning-like electrical arc flash that was visible from New York City and beyond for about a minute on Dec. 27, 2018. Con Edison still is investigating the incident to determine the exact cause behind the failure of equipment at the substation to trip off as designed when the fault occurred at around 9:12 p.m. on that day, company spokesman Bob McGee said.

McGee in a Jan. 2 interview confirmed that no transformer explosion or electric fire had occurred at the Consolidated Edison Inc. subsidiary's substation in Astoria. Instead, the failure of the equipment to trip off in response to the fault resulted in the electricity finding its own outlet and arcing about 20 feet, according to the spokesman. The blue light people saw and the booms they heard were the result of what essentially was a "lightning strike" that occurred when 138,000 volts of electricity connected with the ground, he said.

The arc stopped after approximately a minute when it managed to burn through whatever was stopping the electricity flow, McGee said. Even though some equipment was damaged and an operator in the facility's control room suffered eye irritation from the flash, McGee said the affected substation at 20th Avenue and 32nd Street quickly returned to normal service at that time.

McGee said the utility currently is examining oscilloscope current tracers of the incident to discover exactly how long the arc sustained itself and why the substation's equipment failed to quickly stop the flow of electricity after the fault occurred. "It's abnormal," McGee said, noting that the equipment "normally ... would trip off like a circuit breaker if there was something wrong."

Outside the substation, the incident affected local electric service in northwest Queens with a "transmission dip" that dropped power flow to "as low as 7%," said McGee. "What normally gets supplied in terms of providing your lights to operate optimally at 100% was diminished by over 90% over the course of that minute," explained McGee. "People's lights were dimming so that they were creating this flickering effect."

Although the disruption to local electric service lasted only about a minute, the sudden drop in supply prompted backup generation to automatically switch on at local hospitals, LaGuardia Airport and Rikers Island prison complex, and it affected the New York subway system's Seven Train in Queens for about half an hour as track equipment was reset. Nevertheless, McGee credited the relatively short length of the service interruption to a built-in redundancy within the transmission network.

A report by Con Edison on the incident must be filed with the New York State Public Service Commission within 30 days, McGee said.