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A friend witnessed the explosion of the 14th street substation. I believe these transformers, about 1 city block in extent, delivered power to most of lower Manhattan. I am guessing the flood water obstructed cooling, and they overheated and exploded spectacularly.

(there is a 4 stack natural gas generating station next door to where the explosion happened, so -maybe- the explosion was not the transformer, but most reports say transformer)

My friend reported: 'The power flickered, then came back on'. Some unknown time later the power went out.

So the question is, could power in the grid fed by these transformers stay on for a while after the explosion, and for how long?

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Speculation: there's more than one substation feeding that area of the grid, and the flicker was the system failing over to a different substation. – pjc50 Nov 1 '12 at 16:13
@pjc50, that seems the most reasonable answer, with the delay being the time the other grid takes to realize it can not handle the load. Only question then is, why does all of LM stay dark? Wouldn't they cut in as much of that other grid as they can? – Bobbi Bennett Nov 1 '12 at 16:23
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It takes time for electrons to read and understand the modifications to the schematic which have just occurred. :) – Kaz Nov 1 '12 at 18:52
For a moment, I was considering how much energy is stored in the grid; all those transformers' magnitizing current, and even more if there are capacitors. But c'mon, that would only last a second at most, right? – Bobbi Bennett Nov 1 '12 at 21:59
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In addition to the spectacular failure photos, there is some interesting discussion here about failure modes in various parts of the power transmission system: 205.243.100.155/frames/longarc.htm – mickeyf Nov 2 '12 at 1:50
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1 Answer

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It depends how close you are the transformer and if you are downstream or upstream where if it fails and causes a disturbance and opens keeps the upstream line working or if shutdown for over current.

So the time can be anywhere from 0 to infinity. But if it does fail far away, and you on the grid that is affected by a chain reaction, it can be several seconds with shutdown and followed by a restart and if fault condition is perceived to still be in effect, shutsdown immediately again. The4 phenomena is common because the thresholds for trip on steady power and trip on startup are quite different as startup-surge is normal with incandescent light bulbs taking 10x the current and large motors also taking often more than the breaker rating but for a short period of time.

The algorithm of startup trip current is rather complex and dependant on many factors but safety is paramount. You dont want a short circuit causing a cascade of power transformer overloading, so trip time must be short enough to protect the upstream transformers.

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Thanks for addressing the question. I think you may have missed the situation, it was a pretty big transformer that went. There are clips of the explosion on youtube. Anyway, I now wonder if there isn't a lot of 'spinning' energy in the grid, from all the motors and equipment that don't just stop when the power blows out, they spin down. Just a thought. – Bobbi Bennett Nov 16 '12 at 21:31
Although it would be possible for the motor in something like an escalator to feed some power into the grid if many people are riding it downward, I don't think spinning motors feed into the grid much. I think a bigger issue is that much of the infrastructure is designed so that it can for short periods of time carry more power than it can carry continuously. For example, a particular transformer which had been operating at 75% of its rated power for a long time might be able to operate at 150% of its rated power for up to five seconds before it overheats enough to require shutdown. – supercat Nov 17 '12 at 20:24
If a portion of the grid was fed by two such devices and used 75% of the power that both devices together could handle continuously, then if one device were to fail the other device would be able to feed that portion of the grid for five seconds before it had to be shut down. – supercat Nov 17 '12 at 20:26

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