Adding generator to existing service w/ generator

[Npstewart]

I have a situation where I need to add a generator to back up a whole existing service which is already partially backed up by an existing campus generator. Rather then put all of this in writing, I did a quick & simple sketch to illustrate the issue. The top sketch is the problem, the bottom is my idea/solution.

Input is welcome.

Thanks

 

[jumper]

Is the new generator feeding Panel 1 or both new and existing gennies feeding P1?

I assume existing genny is feeding EM panel.

 

[Npstewart]

Is the new generator feeding Panel 1 or both new and existing gennies feeding P1?

I assume existing genny is feeding EM panel.

The new generator is going to feed the new ATS which will feed existing panel "P1" and "P1" feeds the existing ATS and the existing ATS feeds the emergency panel.

Yes, the existing emergency panel is backed up by the existing campus generator.

This normally wouldnt be an issue because normally you have 1 standby power source, and then a normal source. We essentially will have 2 standby sources now by adding the generator. Both transfer switches would be powered at the same time. Im not sure exactly what the consequence would be but im sure its a code violation and would cause issue.

 

[Chamuit]

Are you going from a partial N configuration to an N+partial N? Or, are you going to use both generators simultaneously?

 

[Npstewart]

Are you going from a partial N configuration to an N+partial N? Or, are you going to use both generators simultaneously?

Both generators need to be able to run simultaneously. The loads in the emergency panel are real "Emergency" loads and the existing generator feeding it is a real "Emergency Generator". The easiest thing to do would just be to remove the existing generator feeder and re-feed it with the new generator however our generator does not meet the criteria for an "Emergency" generator and I dont want to have to get into that.

 

[wwhitney]

Both generators need to be able to run simultaneously.

May I ask why this is? If wired as in your first diagram, during a power outage the new generator will supply all loads(*). If the new generator should also fail, then the emergency generator will come on and supply the emergency loads. So the emergency loads have the same level of protection as usual, why does it matter whether the non-emergency source for the emergency ATS is coming from the grid or a different generator?

Cheers, Wayne

(*) At the time of a power outage, the emergency generator may come on briefly, if the main generator doesn't restore power quickly enough. But the emergency ATS should notice that power is restored from the main generator, and then switch off the emergency generator.

 

[Npstewart]

May I ask why this is? If wired as in your first diagram, during a power outage the new generator will supply all loads(*). If the new generator should also fail, then the emergency generator will come on and supply the emergency loads. So the emergency loads have the same level of protection as usual, why does it matter whether the non-emergency source for the emergency ATS is coming from the grid or a different generator?

Cheers, Wayne

(*) At the time of a power outage, the emergency generator may come on briefly, if the main generator doesn't restore power quickly enough. But the emergency ATS should notice that power is restored from the main generator, and then switch off the emergency generator.

The existing generator is also powering several buildings on this campus. Its very likely that if the power went out to this building, the power would also go out to the adjacent buildings so both generators WILL start and they will be running at the same time. You may have a point if this building was the only building on that campus generator but it isnt. I think the emergency generator powers 6 emergency panels on the campus. Without digging through the code, im sure this is an issue with having parallel power sources like that. There also may be some sort of issue that comes about with backfeeding although I havent fully thought that through.

 

[iwire]

Without digging through the code, im sure this is an issue with having parallel power sources like that. There also may be some sort of issue that comes about with backfeeding although I havent fully thought that through.

The transfer switches prevent anything from being in parallel or back feeding.

By carefully setting the start, stop & transfer delays you select which generator is preferred.

 

[Npstewart]

The transfer switches prevent anything from being in parallel or back feeding.

By carefully setting the start, stop & transfer delays you select which generator is preferred.

So you dont think tapping the new ATS on the line side (Before the generator) is necessary? This would ensure that emergency panel never sees two sources of power.

 

[wwhitney]

So you dont think tapping the new ATS on the line side (Before the generator) is necessary? This would ensure that emergency panel never sees two sources of power.

What do you mean by two sources of power? The new ATS will ensure that the emergency ATS only ever sees one source of power on its "normal" input, either the grid or the new generator.

I'm not that familiar with Article 700--is there a requirement in Article 700 that says that during a grid outage the emergency loads can't be powered by the optional (Article 702) generator, even when there is still an emergency generator and ATS standing by to power those loads should the optional generator fail?

Cheers, Wayne

 

[iwire]

So you dont think tapping the new ATS on the line side (Before the generator) is necessary? This would ensure that emergency panel never sees two sources of power.

Maybe I am missing something but how would two sources make it to the emergency panel with the exsiting ATS in place?

The ATS would have two live supplies at times but it is only going to connect to one of them.


Now I am going a bit off topic, you mention emergency generators. Can we clarify that?

The new generator that is going to feed the entire building is not a emergency generator with only one ATS, that would have to be an Optional standby generator.

The existing one may or may not be an an emergency generator depending on what loads it serves.

The reason I bring this up is that there different rules for emergency vs optional standby.

 

[iwire]

I'm not that familiar with Article 700--is there a requirement in Article 700 that says that during a grid outage the emergency loads can't be powered by the optional (Article 702) generator, even when there is still an emergency generator and ATS standing by to power those loads should the optional generator fail?

Not really sure but I know we do not install like that is the case.

A customer of ours with hundreds of locations often uses two generators on site, a large one that can keep them open and a small one that will supply the emergency loads if both the utility and optional generator go down.

 

[Npstewart]

During a power outage, both generators will start. This means that the existing ATS will receive power from two sources. Somehow, its going to have to choose one of them. The more I think about this, the more I think about this, the more I realize that it needs to always receive power from the "Emergency" generator because its supply emergency loads. However, if the standby was used, and it failed, the power would just switch over to the actual "Emergency" generator.

 

[davidaengelhart]

I see no existing problem to fix.
The level 1 EM generator starts first and supplies the em loads, then the optional level 2 standby starts afterwards and essentially feeds normal power to the em ats through from panel P1 and the em generator shuts down; like what I believe I saw someone else respond with.
Nick, I'll call you.

 

[iwire]

During a power outage, both generators will start. This means that the existing ATS will receive power from two sources.

Yes, the same thing happens every time a generator exercises. Both sources will be at the transfer switch.

In most transfer switches the source connected to the 'Normal' terminals is always the preferred source if both sources are available.

We have a customer that had a co-generation fuel cell that also provided emergency back up (or was intended too) the transfer switch for that had both sources available 24/7/365. It staid connected to the 'Normal' terminals until the utility failed. Once the utility came back it would connect back to utility.

 

[Npstewart]

Yes, the same thing happens every time a generator exercises. Both sources will be at the transfer switch.

In most transfer switches the source connected to the 'Normal' terminals is always the preferred source if both sources are available.

We have a customer that had a co-generation fuel cell that also provided emergency back up (or was intended too) the transfer switch for that had both sources available 24/7/365. It staid connected to the 'Normal' terminals until the utility failed. Once the utility came back it would connect back to utility.

Thanks Everyone. I feel a lot better about this now. Its rare where I run into something I havent done before but this was one of those times. I much appreciate the discussion.

 

[Chamuit]

Little late coming back to the thread...

We have some equipment that is fed by Gen/UPS #1 through the ATS as the Normal/Preferred Source and then Gen #2/Panel-specific-UPS. Kind of similar to what you will have with UPS protection added.

 

[Fnewman]

I don't think I have seen synchronizing mentioned. Unless that function is built into one or both of the generators (not likely since emergency generators are usually either/or with the normal source). When needing to operate in parallel, the second one will have to be synchronized with the running unit. It is also likely the the two units will fight each other for speed control.

 

[Chamuit]

I don't think I have seen synchronizing mentioned. Unless that function is built into one or both of the generators (not likely since emergency generators are usually either/or with the normal source). When needing to operate in parallel, the second one will have to be synchronized with the running unit. It is also likely the the two units will fight each other for speed control.

That shouldn't matter as mentioned above. Your sequence of operation should wind up being Utility (Line 1/ATS 1) with New Generator as the back up (Line 2/ATS 1) which feeds the Preferred Source on the second ATS (Line 1/ATS 2) and the Existing Emergency Generator (Line 2/ATS 2) as that back up.

I'm guessing that these are open transitions? And, you do not have UPS systems to carry the load until the genset picks up? If that is true, there is nothing to synchronize.

 

[Open Neutral]

I was TDY at a USG facility in [SOMEWHERE] & a question came up about exactly which security equipment was on the building generator, and which wasn't. Since this was important, I said "Show me. I want a power fail test...." Amazingly, I got it.

So at 6 pm, we pulled the poco feed. Main generator started, the right lighting came up, but we soon found out that many of the shredders and other classified destruction equipment were oops not generator loads. We also found out the transfer pump to refill the day tank was among the oops.

But the bigger blowback was the comms area emergency generator had failed to start, and their feed was NOT a building generator load. So they were black during our test. Not Good....