SMA sunny boy grid undervoltage

[electrofelon]

This is my first time commissioning a SMA inverter so I am a bit unsure of everything. Just want to get a sanity check on if there is something obvious I am missing before I call SMA. I have two SB7.0 connected to a 120/240 split phase system. System does go thru two transformers before getting to the utility and I have about 8 volts of "rise" at full load, so I have the transformers taps adjusted to give me 115/230 at the inverter outputs with no current. I confirmed this voltage with my meter and the inverters agree. Seems like this should not be a problem: looking at the specs I see a voltage range @ 240 of 211-264. Only thing I can think of is that is "expecting" a different grid configuration, but I dont recall seeing any such setting in the setup.

 

[jaggedben]

Are the inverters still not turning on? You didn't state explicitly if that's the problem.

Is your 8 volts of rise calculated or measured? Did you try turning it on without the taps adjusted down?

I don't see why it shouldn't work though. I'd probably be asking SMA too, if I was sure of the inverter settings.

 

[electrofelon]

Are the inverters still not turning on? You didn't state explicitly if that's the problem.

Is your 8 volts of rise calculated or measured? Did you try turning it on without the taps adjusted down?

I don't see why it shouldn't work though. I'd probably be asking SMA too, if I was sure of the inverter settings.

Its weird. Here is the whole story: At first they fired up and ran fine for a few hours. Voltage was high because at that point the taps were all set at normal. I had about 255 volts. One inverter kicked off, and then the other one a little while later. The LCD displays both didnt display anything which was odd. At that point I was still trying to figure out how to log into the inverter to check settings and codes so I was distracted with all that, but I assumed it was over voltage (even though 255 should have been ok) so I decided to knock the taps down 5%. By that time it was getting quite dark so I aborted for the day. Today, the booted up fine, and the displays were working, but they went into fault immediately for grid undervoltage. I was keeping an eye on it and the lowest I saw was 228. I ran out of time and havnt tried putting the taps back up to normal. Better yet i could go 2.5% which would be in the middle of the two.

Sorry I know my procedure and info is a little scattered. I was running out of light, and trying to figure out the wifi stuff, looking for my WPA2 key, etc. Ill get a fresh organized look at it tomorrow, was just initially wondering if there was some setting I was missing. My understanding is everything should be default, and you need that grid guard key to change any of that stuff. I didnt see anything about grid type or voltage which seems odd.

PS Ok I may have figured it out. I watched a youtube video on the commissioning. I had the wrong "country standard" I assumed it was UL17412010/240 but that appears to be for a delta grid, I should have selected UL17412010/120. Ill try that tomorrow and see if that clears it up.

 

[electrofelon]

UPDATE

UPDATE

Ok that appears to have been the problem. Although the panels were mostly covered with snow all day and it was mostly cloudy, The inverters were on most of the day after changing the setting and exporting about 300 watts per inverter. A few times when the sun was out, i had about a grand on each inverter (each inverter is fed with 8,000 watts of panels).

As usual a little learning curve with a product you're no familiar with, but it is not that intuitive: they discuss this setting in the wiring section, which someone like me just skips over :roll: :dunce: Then when you go through the configuration, even using the configuration assistant, its called "country standard" instead of something like "grid configuration" or "grid type" and it doesnt even explain what the different fields are. I assumed it was just parameters for anti islanding and such and that the one with "240" in it was the one I wanted. So basically, its all SMA's fault and had nothing to do with my lack of knowledge, experience, or not reading the manual

 

[jaggedben]

:thumbsup:

I totally agree that if what is obviously the correct way to set it up doesn't work, then it's the product's fault for being counterintuitive. I see it all the time.

 

[ggunn]

This is my first time commissioning a SMA inverter so I am a bit unsure of everything. Just want to get a sanity check on if there is something obvious I am missing before I call SMA. I have two SB7.0 connected to a 120/240 split phase system. System does go thru two transformers before getting to the utility and I have about 8 volts of "rise" at full load, so I have the transformers taps adjusted to give me 115/230 at the inverter outputs with no current. I confirmed this voltage with my meter and the inverters agree. Seems like this should not be a problem: looking at the specs I see a voltage range @ 240 of 211-264. Only thing I can think of is that is "expecting" a different grid configuration, but I dont recall seeing any such setting in the setup.

The problem with this sort of installation is that the voltage rise at the inverter is proportional to the current output of the inverter, which is changing all the time. Your installation needs for the line voltage to be within the operating voltage window of the inverter both when the inverter is quiescent and when it's running at its maximum output. Voltage drop is of course the culprit, and in general the voltage swing can be reduced by increasing the conductor size, but I don't know if that's possible in your case. Good luck.

One thing that may be possible is to get into the operating parameters of the inverter and expand its operating voltage window, but that's a question for SMA tech support.

 

[GoldDigger]

The problem with this sort of installation is that the voltage rise at the inverter is proportional to the current output of the inverter, which is changing all the time. Your installation needs for the line voltage to be within the operating voltage window of the inverter both when the inverter is quiescent and when it's running at its maximum output. Voltage drop is of course the culprit, and in general the voltage swing can be reduced by increasing the conductor size, but I don't know if that's possible in your case. Good luck.

One thing that may be possible is to get into the operating parameters of the inverter and expand its operating voltage window, but that's a question for SMA tech support.

[MENTION=110304]ggunn[/MENTION]: If you read the last paragraph of post #3, you will see that the original problem has been resolved; it was an incorrect configuration setting (delta versus wye). The problem you describe is a valid one, but does not affect the OP.

 

[ggunn]

@ggunn : If you read the last paragraph of post #3, you will see that the original problem has been resolved; it was an incorrect configuration setting (delta versus wye). The problem you describe is a valid one, but does not affect the OP.

Missed it, thanks. The problem I thought it might be is one of which I am painfully aware. Our installers once moved a transformer interconnected inverter from right next to the tranny to another spot 150' away without telling me, so natch, the conductors did not get upsized.

 

[electrofelon]

The problem with this sort of installation is that the voltage rise at the inverter is proportional to the current output of the inverter, which is changing all the time. Your installation needs for the line voltage to be within the operating voltage window of the inverter both when the inverter is quiescent and when it's running at its maximum output. Voltage drop is of course the culprit, and in general the voltage swing can be reduced by increasing the conductor size, but I don't know if that's possible in your case. Good luck.

One thing that may be possible is to get into the operating parameters of the inverter and expand its operating voltage window, but that's a question for SMA tech support.

There is definitely a bit of voltage rise in the system. There are two transformers and the wire run between them which certainly all add up. On top of that, one of the transformers is older and I think rather lossy. I may upgrade that one. The wire run is #12 at 2400 volts for 2000 feet. Thats a vd of 1.75% at full load solar (16.5KW DC, 60 amps@ 240) which is 4 volts (on the 240 side) and then the transformers of course. I should have gone a little bigger on the wire, but when I designed and installed the system 4 years ago (its not just for the PV) I thought I would be installing only half the PV I ended up with. As I said its hovers around 230 V with no load which is about right, maybe up another 2.5%. I haven't had full sun since I changed the taps and fixed the setting so Ill play with it some more next nice day.