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<p>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. <br>
</p>
<p>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. <br>
</p>
<p>Matt</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 26/2/21 2:30 pm, John Edwards wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAOSsYkqcktho0Qsq6p7XQsNiW3EmM1QzTE7ijRgyxeUuqA4WVg@mail.gmail.com">
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<div dir="ltr">For a truly paranoid setup, you can put an
additional ATS *after* the UPS.
<div><br>
</div>
<div>This potentially lets you replace a failed or failing UPS
without downtime.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>We were able to switch over to mains without downtime and
install a new UPS.</div>
<div><br>
</div>
<div>John</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
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<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, 26 Feb 2021 at 13:33,
Matthew Perkins <<a href="mailto:matt@spectrum.com.au"
moz-do-not-send="true">matt@spectrum.com.au</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">A
generator ATS and UPS setup are not trivial configurations.
The whole <br>
system needs to be engineered by a qualified engineer with
experience in <br>
those sorts of setups. Both for Australian Wiring rules and
also to <br>
ensure all your earth/neutral bonds are at the same
potential. If you <br>
end up with a floating neutral loosing power will be the least
of your <br>
worries. Replacing all the PSU's in all your equipment will
be.<br>
<br>
Typically in a Generator / ATS / UPS setup the UPS is of the
double <br>
conversion type. The UPS output is always in sync with the
mains and the <br>
output of the inverter is always running the load. This is to
cover the <br>
situation where the inverter fails and the UPS goes into
bypass.<br>
<br>
If the mains fail the UPS Sends a signal to the ATS that sends
a call <br>
for the generator to start. The Controller in the ATS then
executes a <br>
per-progamed set of make/break commands<br>
<br>
With respect of output of ATS<br>
<br>
The Mains active is broken<br>
<br>
The Generator Neutral is made<br>
<br>
The Mains Neutral is broken<br>
<br>
The Generator Active is made<br>
<br>
In that sequence you will note the mains and generator
neutrals overlap <br>
this is extremely important if you dont want to let the smoke
out.<br>
<br>
The UPS then detects input from the generator and that the
inverter is <br>
unsynchronized It then starts to slowly adjust the phase to
align the <br>
inverter output within 1% of the generator and and at that
point the <br>
whole thing is shoved back into line.<br>
<br>
When mains is restore the process above is reversed.<br>
<br>
Key things are Earth bonding of generator and neutral overlap
is of <br>
extreme importance a floating neutral even on single phase UPS
systems <br>
can see potential differences of many hundreds of volts to
earth.<br>
<br>
take care<br>
<br>
Matt.<br>
<br>
<br>
<br>
<br>
On 26/2/21 1:41 pm, James Andrewartha wrote:<br>
> Has anyone fed a generator into an automatic transfer
switch? We got a<br>
> generator recently, which is hooked up to some circuits
in our server<br>
> room, that can be manually switched between mains and a
generator. We also<br>
> have an existing UPS that most of the room runs on, and
has a runtime of<br>
> about an hour at the moment. I want to have the ATS fed
by the UPS and the<br>
> mains/generator circuit, so they will be able to use the
UPS until we get<br>
> the generator running.<br>
><br>
> I ask because I was reading APC's documentation which has
these notes:<br>
><br>
>> Do not plug an ATS into a generator without the
protection of a Double<br>
>> Conversion On-Line Uninterruptible Power Supply
(UPS).<br>
>> **Using the Rack ATS with a Generator**<br>
>> APC recommends placing a UPS between the generator
and the ATS input.<br>
>> The UPS will condition the input voltage to the ATS
to prevent<br>
>> thrashing. A second UPS should be used between the
power utility and the<br>
>> other input of the ATS. This UPS will power the load
while the generator<br>
>> starts and stabilizes. The UPS should be sized to
allow time for the<br>
>> generator to be started and the time needed for the
UPS attached to the<br>
>> generator to operate normally. While the generator is
starting, the<br>
>> generator voltage and frequency are not stable. If
the ATS is connected<br>
>> directly to the generator, the ATS can switch to the
generator input<br>
>> before the generator has stabilized. The load of the
ATS will cause the<br>
>> generator voltage to dip. This dip can also shift the
frequency of the<br>
>> voltage. Either of these issues can cause the ATS to
switch to the other<br>
>> input.<br>
> Whereas Eaton says:<br>
>> However, the STS module can also be supplied by one
UPS and another type<br>
>> of source, or by two non-UPS sources providing a
sinusoidal output (AC<br>
>> system, engine generator set, etc.).<br>
> I'm thinking the scenario listed by APC is less likely in
my situation<br>
> since the switch to generator power will be manual, only
after we start it<br>
> up, and that even if the ATS does switch back to the UPS
then the other<br>
> loads (dual-input ones) will remain on the generator, so
the ATS load<br>
> won't be as significant the second time it tries to
switch back. Thoughts?<br>
><br>
><br>
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