That's called a Static bypass and most commercial UPS setup's
incorporate one. These days its the only way you can legally do
maintenance inside the UPS without dropping the load. It's also another
reason why the UPS inverter stays insync with the mains. So the static
bypass can be switched without a big bang. Most Static Bypass systems
also incorporate an interlock that stops you switching to bypass unless
the inverter is in sync with the load or the inverter is shut down and
internal bypass is activated.
It's also sometimes refereed to as an external bypass. Unlike an ATS
they are not usually Automatic and they do not switch the neutral and
earth which remain in parallel only the Active phases are switched.
Matt
On 26/2/21 2:30 pm, John Edwards wrote:
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
<mailto: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?
>
>
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