[RE-wrenches] AC coupling with backup generator in circuit

Kirk Herander kirkh at vermont.solar
Fri Oct 14 08:04:27 PDT 2022

>From an Outback application note:

"Precautions Using a Generator When AC Coupling

Most residential generators, and even some commercial grade generators, are
not designed to
synchronize with another AC source. They may experience catastrophic
failure if the other AC source is
a “stiffer” source and can overpower the weaker AC coupled generator.
To prevent the backfeed from the GTI into the generator, a safety relay can
be utilized that disconnects
the GTI inputs from the Radian AC output bus bars when the generator is
started, either using the
MATE3s AGS generator start function, or some other method."

I'm trying to wrap my head around this concept of a stiff AC source and its
implications for both the GTI and backup generator.
Is it merely a matter of which source (backup genny or PV inverter) has
more kw? Is there any kw ratio of one to the other where the threat of
to one or the other source is real? And I imagine real-time loads being
powered has something to do with it also.

This goes back to an inquiry I posted a few days ago on remote
control disconnect means of the GTI. In this case, I've got a 11kw PV
inverter coupled on the AC bus with a 20kw Kohler generator and 16kw of OB
Radians. The system is grid-tied.

I'm beginning to wonder if a disconnect means of the GTI is actually
required in all cases as Outback infers. But without solid
recommendation to the contrary, I will set it up anyway.

*Kirk Herander / **kirkh at vermont.solar <kirkh at vermont.solar>*

*Owner|Principal, VT Solar, LLC*

*Celebrating our 31st Anniversary 1991-2022!!*


dba Vermont Solar Engineering

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