Regenerative Elevator Issues

[ron]

I realize that 620 has a requirement to do something about absorbing extra energy if there is an emergency generator and a Regenerative elevator. In this case there is no generator.

I'm not sure how to predict if there will be a problem.

600A commercial service and the 2 elevators can contribute 14kW back to the source. I guess it is possible on perfect spring or fall evening that there will be no A/C or heat on and overnight the lights are minimally on, and someone comes into the office to pick something up and takes the elevator.

In reality, I would guess any contribution from the elevator past the actual loads being drawn will just back-end the utility a little. Any practical issues you have found?

Is there an automated device on the market that would sense the back feed to the utility and activate a shunt resister? And if there were a generator, same question about the energy absorbing gizmo mentioned in 620?

 

[steve66]

Just looking at the code, the only note I see about regenerative power is under "Emergency and Standby Power Systems".

So I'm thinking the utility can usually absorb any extra power through the backfeed you mention, and it shouldn't be a problem.

And it also says normal building loads can be used to absorb this power if they are automatically connected to the generator system. My guess is that the building loads will normally absorb the extra power if everything is on generator power.

It sounds like this normally only becomes a problem if the elevator is the only thing connected to the generator. Say for example if the elevator had a dedicated ATS, and for some reason the other ATS's didn't transfer to generator.

 

[Sahib]

If there is a net metering in OP case, some energy saving is possible for the elevator regenerative power of 14kW.

 

[ron]

If there is a net metering in OP case, some energy saving is possible for the elevator regenerative power of 14kW.

In no way do I want to get involved in asking the utility for net metering (backfeeding the grid). That would be painful for this minuscule load.

I will hold my breath and hope this just goes away. IEEE 1547 compliance would be a nightmare for this little dink service.

Thanks

 

[winnie]

I am guessing here, but suspect that the 'worst case' is that the building would simply back feed the grid but that you would get no credit for it. The building demand would go momentary negative, and power would flow to the grid. If you had an old electromechanical meter it would run backward.

Further guessing: the regen inverter takes its voltage and frequency reference from the supply, and is too small to significantly disturb those values.

Further guessing: the regen elevator controller works by letting the DC rail voltage rise, and at a certain threshold starts to synthesize AC back to its input. A standard DC braking resistor could probably be used to prevent regen in all circumstances, and it is probably simplest to have a DC brake resistor that is enabled whenever the generator is running.

The article 620 requirement is there because if you are on generator power the system probably doesn't have the capacity to absorb the extra energy without something breaking, eg. the generator output voltage rising without control.

-Jon

 

[Sahib]

The article 620 requirement is there because if you are on generator power the system probably doesn't have the capacity to absorb the extra energy without something breaking, eg. the generator output voltage rising without control.

-Jon

Actually the generator voltage would rise for capacitive load. In OP case, there would be excessive engine speed. So engine over speed trip, if provided, will be a back up protection in addition to any shunt resistor against elevator regenerative power.

 

[GoldDigger]

But in the OP's (ron's) case there is no generator....

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[Sahib]

But in the OP's (ron's) case there is no generator....

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Correct. But he asked the generator question neverthless :

And if there were a generator, same question about the energy absorbing gizmo mentioned in 620?