Inverter Puzzle

[merkland]

The electrical system in our house is split between two consumer units. One unit has all the heavy circuits and is fed direct from the mains, the second unit has the lighting circuits and two power sockets and is fed through a change over switch either from the mains or an emergency power supply(600w pure sine wave inverter from 24v battery bank).
When our PV system was installed I had them link it in to the consumer unit side of the change over switch, the theory being if the mains went off while PV was producing switching to the inverter would provide a 'mains' and the PV would continue generating to give us an enhanced emergency supply and save on depleting the batteries.
The other day, one of the few sunny days we have had the last two months, we lost the mains supply so no PV generation! Switch to emergency supply and the PV inverter springs back to life but will not connect, it repeatedly went through its test routine but at the end of the routine gave the message Grid Fault W003. While going through the routine it gave the following messages in turn 1. Vgrid 227v - in range. 2. Fgrid 49.9Hz - in range. 3. Measuring Ris0 - 20 with the ohms symbol.
The inverter is a Power One Aurora 3.6. Can anyone tell me what this means and if there is a way to get this inverter to connect to the emergency supply or is my theory up a gum tree?

merkland.

[GavinA]

gum tree I'm afraid.

Your back up inverter and grid circuit is far too small for the grid connect inverter, so any time it might try to connect it'd push the voltage right up and disconnect immediately. Well, something like that anyway.

[BruceB]

I suspect Gavin is right as the W003 message is "grid fail wrong grid parameters" so the voltage and/or frequency are going out of range when it tries to connect

[ecogeorge]

Your grid tie inverter is trying to connect to the grid , -(in this case a pure sine wave inverter) . Unfortunately this will not work as your sine wave inverter is NOT the grid !!
Out of my depth here but all related to "islanding" I think  
But if you purchased a cheap chinese grid tie inverter (search this forum ) I believe they will connect  
runs to increase house fire insurance.!!
rgds George.
Edit to add    http://en.wikipedia.org/wiki/Islanding

[Pat_]

The error message suggests that Riso (isolation resistance) is way too low and this is the reason it won't connect. In practice, as said, the emergency power supply doesn't look anything like the infinite voltage source of the grid, which would hold the voltage correct. In fact if you supplied the emergency power supply backwards with the full current capability of the PV inverter it would pull its voltage up very high and do a lot of damage.

[billi]

Merkland , perhaps it would work , if you grant , that  the power from the Grid tie Inverter  is absorbed in the house  ?

Perhaps  you try it again , when not too sunny , and having a big  load connected to one of your  (off grid ) sockets

The other idea i have is, purchase a MPPT  charge controller  and switch the DC  power cables  going into the Grid tie inverter over to the MPPT charge controller  to charge the batteries

There are some controllers that can handle high DC Voltage

Or get a big off grid inverter /charger

All the best

Billi

[AlanM]

Hi
think it would/could work but you need the power from the gti to go somewhere. I am building an off-grid with a gti pv array using a victron multi. This will be the "grid" that the gti sees but can also take the power from the gti and backfeed it through the charger into the bank. If your gti sees the inverter as grid and tries to input power then prob overloading it. Maybe would work if loads matched the gti output to prevent overload, but output would prob fluctuate and your load matching would have to keep up.

Alan

[Iain]

Hi
Somewhere in the depths of my memory is something about the grid impedance having to be correct as well as voltage and frequency. Not sure but someone else might know.
Iain

[Laurence]

Yes, I am afraid you are going to have a hard time convincing your GTI inverter that the AC from your local 500W inverter is "real" mains, and these GTI inverters are designed to trip out and sulk at the merest sniff of trouble.

Grid impedance is likely the key, here (assuming you've got frequency and voltages OK). The inverter will measure grid impedance by trying to "push"  the incoming power source from (say)230V to 230.1V, and seeing what happens. The real mains, being a very low impedance source, will hardly budge. The GTI inverter will sense this.  Your local mains, unless and probably even if, fully loaded, is going to fly up, when your GTI inverter pokes it. At that point, the GTI inverter smells a rat; it will pull the power and sit back, like it is designed to do.

Remember that the GTI inverter is probing the mains all the time in this way; even if you could present it with a low impedance load for a brief period, something will eventually switch off, the generated AC mains voltage will shift, and your inverter will back off again.