Hello Wrenches,
We are working on a system with three Sunny Boy inverters that feed
into a system that is backed up by a generator. The inverters are
isolated from the generator by relays that open when the generator is
in the warm up stage, before connecting to the electrical system.
What is happening is that the breakers, that connect the inverters to
the grid, trip, . What is apparently happening is that an inductive
effect from the inverter's transformers is causing current rushs
through the breakers when the relays open. This only happens when
the generator is in exercise mode, when the grid is still up and the
inverters are operating.
My theory is that it is much like the ignition system of an
engine. (For the example I'm using a system that still uses
points). When the points open, the voltage rises, because current
will try to continue flowing from an inductor. This raises the
voltage to very high levels. The resulting arc jumps the spark gap.
I think that with the inverters, the high voltage causes a current
surge when the voltage reaches a potential where current will jump
the gap in the contactor.
Has anyone experienced this? Have you found a good solution? We
could retrofit relays on the DC side, but this would not be
convenient. If we use DC relays, is there a downside to
that? Could we use the AC contactor to connect the inverter output
to a large capacitor to absorb the surge? Do we need faster
contactors with a bigger gap? Would the voltages hurt the inverters?
Thanks in advance,
Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP Certified PV Installer TM
Office - 740-448-7328
Mobile - 740-856-9648
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