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How do you calculate the prospective short circuit current for a grid-interactive PV system in order to size switchgear accordingly? Calculating the impedance of the circuit cables on the AC side downstream of the inverters is straight forward but my problem is getting the PV generator impedance, including the inverters. Normally for utility mains you would get the transformer impedance from the transformer itself or use a formula but with inverters i haven't seen anything yet.
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That is actually fairly straightforward:
1. The short circuit current from the GTI is going to be be very strictly limited to the rated output of the GTI with a fudge factor of 1.25 for good measure. Unlike an off grid battery inverter or a generator, there is little or no surge capability in a GTI since the current/power from the panels is strictly limited.
Even a battery powered system is likely to shut down safely when asked to supply more than about twice its rated output current.
The "fault" current will be negligible with respect to the interrupting capacity (AIC) of the switchgear.
2. The real danger will be the fault current from the grid side, and that will be whatever POCO can deliver at the service. You can ask POCO or get a wost case number by obtaining the size and the effective impedance of your service transformer. Nothing special about that computation just because of the PV.
PS: Welcome to Solar Panel Talk Collen!SunnyBoy 3000 US, 18 BP Solar 175B panels. -
Thank you very much, your feedback is priceless to for me as it makes things quite simple and straightforward. Thank you also for welcoming me to the Forum all the way from South Africa.Comment
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