For a truly paranoid setup, you can put an additional ATS *after* the UPS. This potentially lets you replace a failed or failing UPS without downtime.
One time, this saved me because the UPS took a catastrophic surge to its input side, but the inverter and batteries kept powering the network. We were able to switch over to mains without downtime and install a new UPS. John On Fri, 26 Feb 2021 at 13:33, Matthew Perkins <m...@spectrum.com.au> wrote: > A generator ATS and UPS setup are not trivial configurations. The whole > system needs to be engineered by a qualified engineer with experience in > those sorts of setups. Both for Australian Wiring rules and also to > ensure all your earth/neutral bonds are at the same potential. If you > end up with a floating neutral loosing power will be the least of your > worries. Replacing all the PSU's in all your equipment will be. > > Typically in a Generator / ATS / UPS setup the UPS is of the double > conversion type. The UPS output is always in sync with the mains and the > output of the inverter is always running the load. This is to cover the > situation where the inverter fails and the UPS goes into bypass. > > If the mains fail the UPS Sends a signal to the ATS that sends a call > for the generator to start. The Controller in the ATS then executes a > per-progamed set of make/break commands > > With respect of output of ATS > > The Mains active is broken > > The Generator Neutral is made > > The Mains Neutral is broken > > The Generator Active is made > > In that sequence you will note the mains and generator neutrals overlap > this is extremely important if you dont want to let the smoke out. > > The UPS then detects input from the generator and that the inverter is > unsynchronized It then starts to slowly adjust the phase to align the > inverter output within 1% of the generator and and at that point the > whole thing is shoved back into line. > > When mains is restore the process above is reversed. > > Key things are Earth bonding of generator and neutral overlap is of > extreme importance a floating neutral even on single phase UPS systems > can see potential differences of many hundreds of volts to earth. > > take care > > Matt. > > > > > On 26/2/21 1:41 pm, James Andrewartha wrote: > > Has anyone fed a generator into an automatic transfer switch? We got a > > generator recently, which is hooked up to some circuits in our server > > room, that can be manually switched between mains and a generator. We > also > > have an existing UPS that most of the room runs on, and has a runtime of > > about an hour at the moment. I want to have the ATS fed by the UPS and > the > > mains/generator circuit, so they will be able to use the UPS until we get > > the generator running. > > > > I ask because I was reading APC's documentation which has these notes: > > > >> Do not plug an ATS into a generator without the protection of a Double > >> Conversion On-Line Uninterruptible Power Supply (UPS). > >> **Using the Rack ATS with a Generator** > >> APC recommends placing a UPS between the generator and the ATS input. > >> The UPS will condition the input voltage to the ATS to prevent > >> thrashing. A second UPS should be used between the power utility and the > >> other input of the ATS. This UPS will power the load while the generator > >> starts and stabilizes. The UPS should be sized to allow time for the > >> generator to be started and the time needed for the UPS attached to the > >> generator to operate normally. While the generator is starting, the > >> generator voltage and frequency are not stable. If the ATS is connected > >> directly to the generator, the ATS can switch to the generator input > >> before the generator has stabilized. The load of the ATS will cause the > >> generator voltage to dip. This dip can also shift the frequency of the > >> voltage. Either of these issues can cause the ATS to switch to the other > >> input. > > Whereas Eaton says: > >> However, the STS module can also be supplied by one UPS and another type > >> of source, or by two non-UPS sources providing a sinusoidal output (AC > >> system, engine generator set, etc.). > > I'm thinking the scenario listed by APC is less likely in my situation > > since the switch to generator power will be manual, only after we start > it > > up, and that even if the ATS does switch back to the UPS then the other > > loads (dual-input ones) will remain on the generator, so the ATS load > > won't be as significant the second time it tries to switch back. > Thoughts? > > > > > _______________________________________________ > AusNOG mailing list > AusNOG@lists.ausnog.net > http://lists.ausnog.net/mailman/listinfo/ausnog >
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