High voltage on a/c coupled microgrid causing disconnect. VACL2-SRR error.

nemo

I have a Sunny Boy 6000US with around 6kw of panels on my roof which feeds into a microgrid.  There is a Sunny Island 5048 connected to the microgrid via a transformer.

What is happening is that my SB6KUS kicks on in the morning, and produces for awhile and then will hit high voltage on VACL2 and shut off with a *disturbance*, the error I get is either VACL2-SRR or VACL2-BFR (indicating high voltage on L2).  The inverter then goes into waiting mode for a few minutes and the process repeats.  Looking at the spot parameters, the voltage on the bus is around 123 on L1 and L2 and then when the inverter is in waiting mode and then will shoot up to L1:129 and L2:131 after the inverter is producing for a few minutes.  When I measure voltage on the microgrid bus with a multimeter while the inverter is idle, I get 125 volts.  Voltage on the commercial grid is 120. 

I'm not sure why the voltage is getting so high.  Is the sunny island just out of spec with regards to the voltage on the microgrid or is it not sending to the grid correctly?  What troubleshooting steps should I be taking to further isolate my issue?

Dave Angelini

What is the AC voltage on the Island with and without load?  Does the grid inverter work without the island battery inverter in the loop?

Did this ever work correctly? Why is there a transformer on the island? The island is 120vac or stacked for 120/240?

Just off the top of my head so the more you add.....  May get you a better answer.

nemo

Dave Angelini said:

What is the AC voltage on the Island with and without load?  Does the grid inverter work without the island battery inverter in the loop?

Did this ever work correctly? Why is there a transformer on the island? The island is 120vac or stacked for 120/240?

Just off the top of my head so the more you add.....  May get you a better answer.

I haven't tested the voltage on the microbus without the load.

The backup inverter (sunny island) can't really be taken out of the loop.  The Island bridges the microgrid and primary grid.

Yes, it did work correctly.  It was installed in 2009 and has worked pretty well since then.

It is a single island.  The island is connected to a transformer on the microgrid side so that it outputs 240 onto the microgrid, but only connects to the primary grid at 120.

So, there was a scheduled power outage today while the power company works on some things.  During the outage, the voltage on the microgrid is 120-121 and seems to be working as advertised powering my backup loads.  The solar inverter is outputting wattage matching my load (around 1-2kw).  

I'm thinking that for some reason, the Sunny Island is maybe not selling back to the grid which is why the voltage gets high when the grid is connected which was causing my problem.

Dave Angelini

I was going to add that the Island inverter is unbalanced on its input ( L1 only)  but since it has worked for years, unlikely the source.
Unless something has changed? You have SPD's on all of this gear?

Is there not a way to log your power out to the grid?

One of the reasons appliances and electronics last so long offgrid is there is no surge from the grid.
A bad genset offgrid or lightning can be just as bad, but it is in the control of the offgrid home and is usually much more rare.

log on right below. 

nemo

Ok, so here's a rough diagram of my system that I drew up yesterday.  It's the solar inverter that is throwing the error when it sees the voltage go too high.  Both legs are high, but the L2 one is a little higher. 

RCinFLA

Usually caused by too much voltage drop on wiring between main panel and GT inverter.  Gets worse when utility voltage is on the high side.

Pushing current from GT inverter to main panel causes voltage rise on wiring to GT inverter.

Having a 240v to 120v transformer adds more voltage drop.  It also creates a greater phase shifting when GT inverter does its phase pulling to check for valid grid making GT inverter think there is not a valid grid present causing it to disconnect.  Leakage inductance on transformer causes the equivalent of some series inductance between GT inverter and reference grid.  This will allow GT inverter to pull the phase more, possibly to point where it trips invalid grid limit and disconnects.

Dave Angelini

The block diagram helps. Since this worked well for many years the one thing you can easily do is test the system by shutting down the grid input on your main panel. Does the grid inverter charge the battery on a sunny day?

 Talk with your utility also and maybe they will lend you a logging voltmeter.

nemo

So, it just so happened that the day after my original post, there was a scheduled power outage from the utility while they were working on the line.  The power was out from about 10AM to 2PM.  During that time, the solar array produced power to meet my load during that time, between 500 and 1400 watts.  I never had to pull from the batteries because the solar inverter was meeting my load and the voltage on the microgrid hovered right around 120v for the duration.