Need UPS for Emerg. Branch

Designer69

Senior Member
Please see attached riser diagram.

I've got a Natural Gas generator to be used for Emergency power that will supply a life safety branch.

We need to provide either a duel fuel generator (NG & LP) or a NG only with a UPS.

I have two questions:

1) Which is going to be the cheaper option? (Gnl contractor said a 850 gallon LP tank underground can cost up to $10K. A 500 gallon tank is only $2k. This is an issue I can resolve with the generator people as far as the right tank size.)

2) On the riser diagram, where is the best location to insert the UPS on the Em. branch? Right upstream of the ATS?


Thank You
question.jpg

Better Pic Here: https://imgur.com/a/rhQBiNw
 

victor.cherkashi

Senior Member
For 60kw ups and battery most likely you need a room, ac or ventilation. Also ups usually can't give high start current. My gross analysis says that ups will be more costly.

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myspark

Senior Member
Please see attached riser diagram.

I've got a Natural Gas generator to be used for Emergency power that will supply a life safety branch.

We need to provide either a duel fuel generator (NG & LP) or a NG only with a UPS.

I have two questions:

1) Which is going to be the cheaper option? (Gnl contractor said a 850 gallon LP tank underground can cost up to $10K. A 500 gallon tank is only $2k. This is an issue I can resolve with the generator people as far as the right tank size.)

2) On the riser diagram, where is the best location to insert the UPS on the Em. branch? Right upstream of the ATS?


Thank You
View attachment 21453

Better Pic Here: https://imgur.com/a/rhQBiNw
Please see attached riser diagram.

I've got a Natural Gas generator to be used for Emergency power that will supply a life safety branch.

We need to provide either a duel fuel generator (NG & LP) or a NG only with a UPS.

I have two questions:

1) Which is going to be the cheaper option? (Gnl contractor said a 850 gallon LP tank underground can cost up to $10K. A 500 gallon tank is only $2k. This is an issue I can resolve with the generator people as far as the right tank size.)

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You already have the answer to question No1 . . . so I won't comment on that.

With regard to Question No 2


2) On the riser diagram, where is the best location to insert the UPS on the Em. branch? Right upstream of the ATS?


If you insert the UPS upstream of the ATS, you essentially have no choice but to hook up your UPS after the Emergency Generator. This is your criterion in your first sentence of your post.


Hooking up the UPS after the ATS would have your panel fed from either normal power source or the Emergency Power (Generator)


As a side note:
Don't get confused about the difference between Un-interruptible Power Supply (UPS) vs Emergency Power Supply. (EMS)


UPS is short-lived maybe lasting several minutes while EMS could last hours or even days.


UPS is mostly for data centers where loss of data is critical. . .even for a second or a cycle of the sine wave.


You will also find on rare installations, like robotics where machine has to be in the “home” position during power failure.


Emergency Power (EMS) mostly in hospitals and in critical operation where a momentary loss of power can be tolerated.

FWIW:
Uninterruptible power systems design are applied to specific circuits that power specific load or loads because of their limited power sustenance.
 

Designer69

Senior Member
Hah good point. It obviously has to be put in after the ATS, otherwise the UPS battery isn't charging during normal power.

Only question is.. is there any backfeed concerns during ATS switch over? (UPS supplying power to the Utility momentarily just before the switch is made)

Thanks
 

myspark

Senior Member
Hah good point. It obviously has to be put in after the ATS, otherwise the UPS battery isn't charging during normal power.

Only question is.. is there any backfeed concerns during ATS switch over? (UPS supplying power to the Utility momentarily just before the switch is made)

Thanks
While you are drawing power from the Emergency source, you are not connected to the grid.

Conversely, when connected to the grid, you are not connected to the generator.

So, no connection to the utility grid...no feedback from your Emergency system.

I see that your concern is during the transfer period. The perceived feed back to the utility is of less concern than the motor loads that are connected to the system when the transfer was made.

The ATS (not those “cheapo” ones) do have time delay that allows connected load to “settle down” like motors for refrigeration units, positive displacement pumps and other motors that deliver kinetic energy like motors with flywheels.

AC units develop pressure in the system that stay while the motor is idle for a certain amount of time. If you restart the motor after the momentary loss of power, it will suffer a lock-rotor condition. You need to allow the pressure to equalize before restarting.

Some designs will recover without any adverse effect. Synchronous motors that are still turning when you make the transition will suffer damage or draw a lot of current because the grid power is not in-sync with the generator before the power was transferred. This usually takes place that will cause circuit breakers to trip.

If you decide to make a DIY Automatic Transfer Switch, just make sure you have enough time delay to allow this “settling down” episode.
 
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