[RE-wrenches] Why are RSD devices burning up?

[William Miller]

Wrenches:



I came across this U-tube video that I think is relevant:
https://www.youtube.com/shorts/Lyfdr1AWzU4



A factor that aggravates the arc producing and sustaining characteristics
of solar circuits is the nature of the IV curve.  One can short solar
circuits and create a zero volts situation.  Once that short first opens,
the voltage climbs quickly, sustaining the arc even more than the video
demonstrates.  I think we all need to remember this concept when
considering our designs and installations.



It seems to me that the fiery RSD failures that have been described here
are more than likely due to the RSD devices opening PV circuits under
load.  This is like disconnecting MC connectors under load.  An arc will be
created and is likely to sustain for some time.



If we could contrive systems that removed the load from PV circuits just
prior to RSD activation this problem might be resolved.  It may not be that
difficult to achieve this.  In theory, if the RSS system first disconnected
the AC feeder to the inverter and then after a short delay the RSS
activated, the RSS devices would not be opening under load.  In its most
crude form a contactor on the AC circuit would be opened by the RSS
initiation device and then shortly thereafter the PV RSDs could open
without arcing.



I have often thought that PV inverters should have an “inhibit” circuit
that, with the opening of a low voltage contact, the inverter would shut
down.  Many power electronics have this feature.  FXR inverters have this.
The inhibit function could be used to take the load off of PV circuits
prior to rapid shut down.  Also, the inhibit function could be used to
protect batteries in AC coupled systems without the need for high amperage
AC contactors.



William Miller



Miller Solar

17395 Oak Road, Atascadero, CA 93422

805-438-5600

www.millersolar.com

CA Lic. 773985
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