Inverter reporting high utility voltage

[JoeDaddy7105]

Hello,

I have a Solar City (SC) system on my house that was put in about 2 years ago. The system has been running fine until a few months ago when SC called me and said my inverter was measuring voltage above 252Vac on the utility side. In several cases it was measuring up over 300Vac on the utility side. This has been happening on and off for the past few months and the high voltage last for anywhere between a few minutes to several hours. Yesterday my inverter was down all day because it was seeing high utility voltage but today it is back to normal.

When this first started happening I waited to catch the inverter measuring this high voltage issue so I could try to check it with my multimeter. Everytime I measure with my multimeter when it has this issue I am unable to see the same high voltage. My measurements are between 248-250Vac at the main breaker, at the back feed breaker to the inverter and even at the dryer outlet. I also borrowed a power quality analyzer from work and hooked it up to record voltage for a week. The highest it measured was 250Vac.

SC sent a tech to check the system a few weeks ago. The high voltage condition was not happening when the tech was on site so he did a few visual inspections of the inverter and then he pulled up the log files from the inverter and continued to say it appears to be a utility issue. I also asked SC to check my neighbors systems because I have several people in the area who have SC with two of them being right next door and they did not see any of my neighbors inverters reporting the same issue. SC continues to blame the utility despite no evidence outside of what the inverter is measuring to say it is the utility.

SC claims they are measuring utility voltage at the inverter and also at the panel with a Power Blaster. The Power Blaster is setup to measure utility consumption which feeds into the SC dashboard so we can see utility consumption vs PV production. I can see the CT donuts for the Power Blaster on the utility main feeders in my panel but I am not sure where the voltage measurement for it is coming from.

I cannot verify the high voltage reading SC is getting so I have a pretty good feeling something is faulty with their measurements or the inverter has a short and is pushing higher voltage into my panel but it is getting diluted by the normal utility voltage. It seems suspicious that none of my SC neighbors are having this issue.

Has anyone seen an issue like this? Can the CTs also measure voltage? Any tips on troubleshooting this issue that a wavy DIY homeowner can do?

My inverter is a Solar Edge brand and the PV system is wired in to my main panel as back feed system with a net meter on the utility.

Thanks for any help you can provide,
Joe

[inetdog]

A report of high voltage at the inverter terminals comes from a combination of two factors:
1 High voltage from POCO at the service entrance (where you never measured above 250V), and
2. Voltage difference (increase, not drop) between the inverter output terminals and the service entrance. This could be caused by too small a wire size, too long an AC run for the wire size, or problems with connections along the way.

If the reports from the inverter come mainly when you are not running much if any local load, then there is a good chance that the second factor is a significant contributor.

[NEOH]

I find it hard to believe that you actually have 300 V AC on your Main Panel Lugs.

CT's are "current transformers" - they measure amps.
Is there a small wire that actually makes an electrical connection to the AC Power wire?
That extra wire could sense the voltage.

In the Main Panel, turn the Dedicated PV Breaker Off-On a few times to re-seat the contacts.

With power off - verify all connections are tight ...
a) Verify the connections on the Dedicated PV Circuit Breaker in Main Panel
b) Verify the connections inside the PV AC Disconnect (outside)
c) Verify the connections inside the Inverter

Verify all Grounds are tight, too

Verify the voltage from L1 to Neutral and L2 to Neutral are equal.
Just maybe, you have a faulty neutral?

Can you borrow or rent a Fluke Data Logging DVM ?
Record the voltage history ...
First connect it to the Inverter side of the Dedicated PV Circuit Breaker in the Main Panel
If OK then connect it to the Inverter's AC output.
If OK then the Inverter is faulty.

[JoeDaddy7105]

I took a closer look at the Power Blaster in my main panel and I understand now where it is measuring voltage (see attached image). The PB itself is connected to a dedicated 15A breaker (small black wire along the left side of the panel in the attached pic). Near the voltage connection to the PB, there is a blue splice where the installers tapped the red and black wires together. While the PB may be reporting 240+V, it is actually just seeing one 120V leg two times to make it think it is seeing 240V. So if the PB is seeing 300+Vac then it is actually just seeing 150+Vac on one leg instead of measuring both. I presume the Inverter is actually measuring the 240V from both 120V legs combined. Everything from the back feed PV breaker to the inverter is SC territory but the next time I catch the issue happening I will do some closer measurements to the PB connection.

The power quality analyzer I borrowed from work is a Dranetz which I set to record voltages every 5 minutes for 5 days and that is where I didn't see anything over 250Vac while the PV system had several periods of being off due to high voltage. I was not able to get the Dranetz connected at the main lugs because my panel is outside and I didn't want to leave the panel open for several days. There is a spare dryer outlet in the basement that is not far from the panel that I was able to connect the Dranetz to and I think it would be pretty impossible for there to be 300Vac at the main lugs with nearly 50V drop through the panel and down 10-15ft of wire. When everything is in the normal range the Dranetz is reading nearly the same voltage as what is being reported on the inverter screen.

The odd thing is that this just started happening a few months ago and my PV system has been in operation for nearly 2 years without this condition so I don't see how the wires from the inverter to the main panel could suddenly be too small and cause a drastic spike in voltage. We also have not change our energy usage patterns or installed anything new that would cause our demand to go up or down by very much.

I'll try to check some more connections and see if I can get the Dranetz on the main lugs for a few hours when I see the condition happening to try to narrow this down. It has been frustrating because SC keeps insisting there is actually 300V at the main lugs despite what I have told them I have measured and recorded and my utility (Xcel) doesn't think it is their issue either. If I was able to confirm the SC equipment reading of the high voltage then I would be demanding that Xcel come out and fix the issue but until I can confirm there is a high voltage issue, I standby it being a SC issue.

[max2k]

I took a closer look at the Power Blaster in my main panel and I understand now where it is measuring voltage (see attached image). The PB itself is connected to a dedicated 15A breaker (small black wire along the left side of the panel in the attached pic). Near the voltage connection to the PB, there is a blue splice where the installers tapped the red and black wires together. While the PB may be reporting 240+V, it is actually just seeing one 120V leg two times to make it think it is seeing 240V. So if the PB is seeing 300+Vac then it is actually just seeing 150+Vac on one leg instead of measuring both. I presume the Inverter is actually measuring the 240V from both 120V legs combined. Everything from the back feed PV breaker to the inverter is SC territory but the next time I catch the issue happening I will do some closer measurements to the PB connection.

The power quality analyzer I borrowed from work is a Dranetz which I set to record voltages every 5 minutes for 5 days and that is where I didn't see anything over 250Vac while the PV system had several periods of being off due to high voltage. I was not able to get the Dranetz connected at the main lugs because my panel is outside and I didn't want to leave the panel open for several days. There is a spare dryer outlet in the basement that is not far from the panel that I was able to connect the Dranetz to and I think it would be pretty impossible for there to be 300Vac at the main lugs with nearly 50V drop through the panel and down 10-15ft of wire. When everything is in the normal range the Dranetz is reading nearly the same voltage as what is being reported on the inverter screen.

The odd thing is that this just started happening a few months ago and my PV system has been in operation for nearly 2 years without this condition so I don't see how the wires from the inverter to the main panel could suddenly be too small and cause a drastic spike in voltage. We also have not change our energy usage patterns or installed anything new that would cause our demand to go up or down by very much.

I'll try to check some more connections and see if I can get the Dranetz on the main lugs for a few hours when I see the condition happening to try to narrow this down. It has been frustrating because SC keeps insisting there is actually 300V at the main lugs despite what I have told them I have measured and recorded and my utility (Xcel) doesn't think it is their issue either. If I was able to confirm the SC equipment reading of the high voltage then I would be demanding that Xcel come out and fix the issue but until I can confirm there is a high voltage issue, I standby it being a SC issue.

I can't make much from the picture in terms how PB senses voltage: it needs at least 'reference' point and with both voltage inputs connected together it is not supposed to even work- where it gets neutral from to get at least some energy to power itself up? Basically one more wire is missing from the picture. Unless of course they use EGC through the enclosure screws but that would be strange to say the least.

I could see how it would work if they connected both wires to separate phases - PB could get power being connected to 240AC source in that case and it could measure it too.

Basically I doubt SC can get any data from that PB so they're left with only one source of data- inverter itself which is having problems to begin with. That would explain all your troubles. Now as you stated all of that is 'SC territory' which probably means they own it (I'm not clear how SC arrangement works) you'd only need to prove to them that your main voltage never went out of range. IMO you already did this as your logging through dryer connection was correct: the wires from MSP to the dryer were not under load and as such there was 0 voltage drop. You don't really need to be on MSP lugs to measure voltage there.