Grid Tied Grief!

[Mike90250]

You better get the installer or a rep from the power company out there to see what's going on. With 3 phase, transformers and grounding weirdness at Kv levels, you don't want to be throwing buckets of water around

[jflorey2]

So I have 53 V DC from DC+ and DC- (checking AC) to ground but as stated above it may disappear under a load to zero I have not tried this but very possible but when I test DC+ to earth ground (DC setting on meter) I get 112V DC and then checking DC- to earth ground I get 271v DC. Is this normal?
Now because I am not an electrician I am just asking, would it be considered wrong to connect DC- to earth ground? To be clear it is not now but was wondering.

That is generally not a good idea on transformerless (non-isolated) inverters. They must be left "floating" - although that term is somewhat deceptive because the inverter does not allow the array to truly float; it pulls it to a specific voltage depending on the design of the inverter. (Note that the frames must still be grounded.)

[gtuplin]

You better get the installer or a rep from the power company out there to see what's going on. With 3 phase, transformers and grounding weirdness at Kv levels, you don't want to be throwing buckets of water around

My service is simply 240 single phase, I was describing the transmission lines above. We are in no way tied into that system

[gtuplin]

That is generally not a good idea on transformerless (non-isolated) inverters. They must be left "floating" - although that term is somewhat deceptive because the inverter does not allow the array to truly float; it pulls it to a specific voltage depending on the design of the inverter. (Note that the frames must still be grounded.)

Ok so you are saying that it is not the normal but can be done? Without damage of coarse, just wondering if that would solve this issue? All the modules are well grounded.

[DanS26]

I may be wrong, but I think you said the the five inverters on your property are the same make and model. Although I looked at the Growatt 8-10 MTLP-US spec sheet it did not say whether these inverters can be separated from the wire box. If they can be swapped, maybe you could swap the house inverter with one of the four ground mounts.

[gtuplin]

I may be wrong, but I think you said the the five inverters on your property are the same make and model. Although I looked at the Growatt 8-10 MTLP-US spec sheet it did not say whether these inverters can be separated from the wire box. If they can be swapped, maybe you could swap the house inverter with one of the four ground mounts.

The house system is running less panels but same inverter, I also have a spare inverter so may have to do a test with it and some extra panels to confirm it's good then trade places with one of 4. Why not its an elimination game at this point.

[DanS26]

I'd swap the house inverter since you know it operates properly.

[sensij]

That is generally not a good idea on transformerless (non-isolated) inverters. They must be left "floating" - although that term is somewhat deceptive because the inverter does not allow the array to truly float; it pulls it to a specific voltage depending on the design of the inverter. (Note that the frames must still be grounded.)

If one of the DC legs were to be connected to ground on this design of inverter, it should probably trip the inverter's ground fault protection.

[jflorey2]

Ok so you are saying that it is not the normal but can be done? Without damage of coarse, just wondering if that would solve this issue?

In all the transformerless inverters I have seen, the manuals explicitly say to not ground either side of the PV input. I don't know if that's the case with yours but it likely is.

You might want to check out the "ungrounded PV systems" article from Home Power magazine (search for it.) It gives a good overview of ungrounded systems and how they work.

[gtuplin]

Well electrician came and tried the ground but as most expected it did not allow the inverter to go past self test and came up with isolation error.
I seem to be riding a slippery slope and the electrician has decided to contact Growatt and see if they have a solution but might try swapping inverters to see what happens. I have to take a day or so off of this before it drives me to drink!
Hope to hear from tech soon.

[sunnyguy]

Did you try to repeat the bucket test? Did you ask the utility to check the transformer earth ground?

[gtuplin]

Did you try to repeat the bucket test? Did you ask the utility to check the transformer earth ground?

It rained today so unable to re enact that bit of excitement but the inverter (only one on today) was acting so stupid I had to walk away! It was semi cloud rain occasional sun burst today but the inverter would hit highs of 8000 (never had numbers that big) then start a drop that would take about 5 minutes to reach 0 then sit at 0 for about 30 seconds then begin the climb again to re enact cycle. Occasionally it would turn right off in the middle of the day but the climb and decline were about the same once it decided to start up.
I told the electrician to make the calls to hydro and Growatt. , I am sure they will take him more seriously. I have not heard from him yet.
Moisture seems to be the common thing right now but it seems over my head!
Will turn them on one at a time tomorrow to see what crazy display of hell is created.

[adoublee]

Has your electrician monitored frequency on the AC side during this power swings that are unrelated to irradiance...?

[sensij]

It rained today so unable to re enact that bit of excitement but the inverter (only one on today) was acting so stupid I had to walk away! It was semi cloud rain occasional sun burst today but the inverter would hit highs of 8000 (never had numbers that big) then start a drop that would take about 5 minutes to reach 0 then sit at 0 for about 30 seconds then begin the climb again to re enact cycle. Occasionally it would turn right off in the middle of the day but the climb and decline were about the same once it decided to start up.
I told the electrician to make the calls to hydro and Growatt. , I am sure they will take him more seriously. I have not heard from him yet.
Moisture seems to be the common thing right now but it seems over my head!
Will turn them on one at a time tomorrow to see what crazy display of hell is created.

Short periods (up to about 15 min) of very high power output is normal behavior when there are passing clouds. Reflections off the sides of clouds combined with the unobstructed sunlight can increase the irradiance on the array to much more than the standard 1000 W/m2 at which the panels are tested, and the resulting output can be higher than nameplate.

[gtuplin]

Has your electrician monitored frequency on the AC side during this power swings that are unrelated to irradiance...?

Well I'm not sure if that test was done but if nothing else I have great respect for my electricians meticulous work ethics and hanging in there trying to resolve this issue!

So I did unpack the new spare inverter and set up a string of panels to test about 600 feet from other site and found that it acted similar to the large field, although the radical behavior was less but the very low out put was similar. We had a call back from hydro today and they seem very concerned and have placed an order to send out a crew to check for unusual harmonic distortion as they noted that they had a similar situation a few years back. not a lot of info from them but its a good step! also waiting for feed back from growatt. So its either 5 dickered inverters or harmonic distortion and I suppose both are possible! I was wondering if the new 50kv transformer could cause distortion like that?
Anyways I have shut down everything in fear of damage to equipment and will wait for hydro to show up, will update when I have info.