620.91 Emergency and Standby Power Systems

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GoldDigger

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Thanks that makes sense

It is the same sort of thing that requires installing a braking resistor in a VFD. Without provision for it, the elevator or other equipment would have to coast to a stop (not great if you are in the elevator) or rely entirely on mechanical braking (which might be damaged in the process.)
So your initial post was very close to correct.
 
Thanks Golddigger, the reason why I posted this subject was in the reading of the article and coming across the word "regeneration" I thought of a VFD which operated a refridgeration compressor and when it was stopped by the controller sometimes it would fault out in "regeneration" turning backwards,its a DURA that I am speaking of,good drives though. But the Code is so intense to throw that in for us think about. How do we suppress these surges and or sustained feed back?
 

GoldDigger

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...How do we suppress these surges and or sustained feed back?

In the case of an elevator, it is not something to suppress, it is part of the design of the machinery. It is easier on the hardware to use the grid as a brake than to work without regenerative feedback. Not to mention costing less for power if the other loads in the building can utilize it. :)
That is the reason it is so plainly called out in the code.
So when the alternative power source is in use, there has to be a switchable load provided to dissipate that regenerative power when there are not enough regular loads in operation. The generator simply cannot absorb backfed power, nor can the typical battery-powered inverter.
 
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GoldDigger

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620.91(B) talks about other building loads being auotmatic, does that mean auto transfer switching, to a panel to absorb this regenerated power?

IHMO it means just what it says, paraphrased as:

If there are normal building loads which you can be sure will be turned on whenever the elevator (or other regenerative load) is operating and which added together are as large as or larger than the maximum regenerated power, then you can rely on them to absorb that power.
But you must automatically or manually transfer that group of loads to the same(!) generator or paralleled generator system at the same time that you transfer the elevator to the generator. There cannot be any way that the elevator could be transferred without sufficient other loads being transferred too.
To me that means that if there is more than one automatic transfer switch involved, the elevator switch must not transfer unless the other load switch does too. In the case of a manual transfer switch (unlikely or maybe not permitted), the same switch must make both transfers.

And as a design concern, I would want to be assured that nobody would go around turning off all of the lights, etc. while leaving the elevator running!

As a side note, if no normal loads are sufficient, then some other power absorbing load must be arranged. And if you do not want the generator powering that load full time, you would need some arrangement that switches that load on whenever a power meter (NOT just an ammeter) connected to the elevator feed determines that regenerative power is being produced.
 
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