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magoo2 (Electrical) (OP)
6 Feb 12 18:20
Can someone describe the zero sequence impedance of an inverter?  I've heard it described as a delta winding in a transformer, so it is just an open circuit.  So if I have a generator or photovoltaic array behind it, it doesn't matter since the open circuit is there for the inverter.

Can someone validate this assumption.  Thanks.  
davidbeach (Electrical)
6 Feb 12 19:47
Inverter as in power electronics, or inverter as in packaged UL-1741 compliant assembly complete with isolation transformer?
magoo2 (Electrical) (OP)
6 Feb 12 20:11
UL-1741 compliant inverters.
davidbeach (Electrical)
6 Feb 12 20:50
Zero sequence impedance of the "inverter" will be essentially indistinguishable from the zero sequence impedance of the isolation transformer.
magoo2 (Electrical) (OP)
7 Feb 12 8:51
I'm not sure exactly what you're saying.

If I have a delta grd-wye isolation transformer, then I get a break or open in the zero sequence.  So I get no contribution from the inverter for a single line to ground fault on the primary or secondary of the stepup transformer.  Is that what you're getting at?
Helpful Member!  davidbeach (Electrical)
7 Feb 12 9:34
The UL-1741 packaged "inverter" (assuming 3-phase) all most certainly contains an isolation transformer that is delta on the power electronics side and grounded wye on the system side.  This is necessary to meet the IEEE-1547 requirement to be compatible with the utility grounding system.  As such, the isolation transformer functions as a ground source just as any other grounded wye-delta transformer would.  The zero sequence impedance of the "inverter" is just the zero sequence impedance of the transformer and the power electronics are open circuited in the zero sequence (probably connected in delta anyway).
magoo2 (Electrical) (OP)
7 Feb 12 13:09
Many thanks, David.

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