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?
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