3W vs 4W Inverters and Ground vs Neutral

[spc300]

We are seeing 3W inverters desiring interconnections to the solidly grounded power system from PV systems. There is an issue as to how does this type of a 3W system perform a phase-neutral voltage protection measurement as required in the 1547 standards etc. There is a desire of the interconnector to use a bonded 4th wire as the ground/neutral which is not safe.

 

[waross]

L1, Neutral, L2, Ground. Four wires. Am I missing something?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[spc300]

The issue is that the ouput of the inverter provides only L1,L2,L3, rather than the more conventional L1,L2,L3,N. They are bonding the frame to earth and then trying to call that the neutral. This is driven by a PV array.

 

[rbulsara]

You will need to have delta-wye transformer right next to the inverter to get a neutral for a separately derived, grounded system system.

In theory you can parallel a 3 wire system with a 4 wire system and it becomes a non-separately derived system. You will not able to feed single phase load from the PV system alone, but you can certainly feed power back to the grid.

What is 'desiring" ? They are either made and approved for grid connection or or not. Isn't there a manual with those inverter?

Rafiq Bulsara

http://www.srengineersct.com

 

[davidbeach]

Any UL-1741 inverter will comply with IEEE-1547 clause 4.1.2. In simple terms, and three-phase inverter will, within the UL-1741 package, include a delta-wye transformer. This is a separately derived source and all of the grounding rules for separately derived systems apply.