The green-blue glow that filled the New York City sky was not caused by a transformer explosion, Consolidated Edison clarified:
The extraordinary event had in fact been traced to a voltage monitoring gizmo known as a coupling capacitor potential device — or CCPD if you happen to operate a power grid — that failed to function properly at a Queens substation on Thursday night.
That led to an arc flash in which electricity delivered via a 138,000-volt transmission line jumped from one point to another, ionizing the very air through which it leapt. The energy was too great to be constrained to a straight trajectory, and it began to arc with its own power. The arc grew higher and higher, as did the heat it generated.
“Temperatures can reach as high as 35,000 degrees Fahrenheit,” notes a General Electric fact sheet. “This is hotter than the surface of the sun.”
The fact sheet adds, “Arc Flash temperatures can… liquefy or vaporize metal parts in the vicinity.”
Some of the substation equipment is aluminum, which normally casts a silvery white light when it burns. But at extremely high temperatures such as this bit of sun in Queens, the light generated by the vaporized aluminum was the almost-Tiffany blue that New York City residents saw rise into the sky and spread through the low-lying cloud cover.