Inverters shutting down - why?

[guydewdney]

I have a Power-one Aurora 3.6kw grid tie inverter runnign fine.

Its rained here a lot - so I thought it was time I fired up the second one. Connected it in parallel to the first - and as soon as it tries to make power (not as soon as it wakes up) BOTH inverters shut down with two error codes - E18 and E7

E18 has a 'value' of 0.006 or 0.008 and means 'ground fault'
E7 means 'IGBT saturation'. I dont know what that is.

Both inverters have the same faults recorded

Everything is earthed correctly, and a basic test shows a resistance of 0.1ohm max. All wires have been wiggled and checked.

Any ideas?

[wyleu]

No direct experience on this sort of thing, but it sounds a little bit like an earth loop or a single turn transformer.
If you have a loop of conductor and there's magnetic fields around you can induce considerable current in the loop This could well be doing unpleasant things to the IGBT  http://en.wikipedia.org/wiki/Insulated-gate_bipolar_transistor( that's one of the electronic switches that chop up the DC to start it on it's journey to AC).
It might be that as a result of closing an isolator you could have introduced a loop which is acting like a transformer. It's one of the reasons you don't bolt transformers down except with a bolt from one side.

Please feel free to ignore this if better ideas come along.

[RichardKB]

Have you tried both of them seperately on their own first to make sure both are still working OK.

Rich

[guydewdney]

Disconnect #2 and #1 resets itself, and carries on as normal.

It takes a few seconds for the fault to occour - when I connect #2 to the mains, it then should produce 500 to 1000 watts at the voltages I am running at. Nothing happens - the computer shows incoming volatge at 500 odd volts, power in at 9 watts (enough to run the inverters computer) and power out at zero. Then a few seconds later (5 to 10) it shuts down. Inv #1 shuts down the instant inv#2 should connect, not after the 5 second delay.

I'm wondering if its duff...

[Alan]

Are you connecting them on the same phase. ?

If you are you can not connect them with out one inverter being fed from a double isolated transformer.

The Sunny / Windy Boy inverters have there own double wound isolation transformers built internally so you can connect as many as you like to a phase.


If the D.C. input volts are totally isolated from the other inverter you can connect as many as you like to one phase.

If the D.C. volts are the same to both inverters then you need a double wound transformer connecred to one of them.

Regards

Alan

[guydewdney]

I have both connected them to the same and different phases.
The same result either way.

The manual http://www.power-one.com/resources/products/appnote/AlternativeEnergy/manual_installation_pvi-3600-outd-uk-f-w.pdf doesnt mention anything about isolating transformers.

The DC side should be totally isolated - each is fed from it's own 'wind interface' (which is a bridge rectumfrier, amongst other things).

The only things that are common are the neutral, the earth, and the room they are in... Oh - and the RS485 connection (which I have checked is correct - and have disconnected to see if the gnd connection was a problem - it wasnt.)

[Alan]

Is there a separate three phase alternator feeding each Inverter ?

If you are feeding each wind interface from only one alternator you will not achieve isolation.
A three phase bridge rectifier / capacitors  will not achieve isolation.

If both inverters are fed from a common three phase alternator it will not work
unless one inverter has got a double wound transformer connected to the A.C. Side.

Try this link

http://www.steamboilers.homecall.co.uk/AURORA1.pdf


Regards

Alan

[guydewdney]

almost - but theres two wind interfaces.

off to bed - 1.45am 2010 jan 1st...

[Alan]

You need to re read my posts.

It will not work.

It will destroy both inverters.

A wind interface is just a three phase bridge rectifier, an I.G.B.T. Fet to switch in a dump load and some capacitors for smoothing.

IT will not give you the required isolation.

The impedance of the transformers matters, a bit of thought needs to go into that one.

Regards

Alan

[guydewdney]

Does it make any difference that each inverter is feeding a different phase?

I'll contact the manufacturer when they get back to work - in the mean time - it will stay off!

Guy

from the installation manual:-
This model of AURORA is transformer-less, that means that there is no galvanic
isolation between input and output. This allows an increase the inverter efficiency.
AURORA is equipped with all the protection needed to operate safely and to
comply with existing safety regulations even without an isolation transformer.
 

[h1267]

found this on the net it might help you out with what you need to do
http://www.solacity.com/AuroraStack.htm
hope this helps
http://www.solacity.com/Docs/Dual-Inverter%20Wiring.pdf

[Alan]

The only difference  here is that solid state relays are used. The contactors they suggest would consume energy while connected.  The solid state relay connects the transformer to the grid live side when the D.C. Voltage on the inverter inlet is > 60 volts.

I have used transformers when earth faults develop on the turbine until the turbine can be repaired.

Regards

Alan

[guydewdney]

I found the same stack discussion.

The primary difference, that I dont understand - is that the version being discussed is single phase output, I have two phase. I can see how single phase will cause problems - Im just being thick wrt two separate phase outputs.....

[rogeriko]

Dont forget on the two phases the neutral is common to both

[guydewdney]

And neutral is identical to earth (in my case) - yes.