2 SB 3800 Inverters, 9600 kwp array, one 60m export cable. Inverter cutting out?

[Blueflash]

I have a recurant problem on a system which one inverter gets a AC fault. This happens alternately, either one inverter or the other. The fault seems to be at peak output but does not trip any breakers. The system is very wrong in the fact its all on the one phase (as only one available), but this should not cause an inverter drop out.
Both inverters are in close proximity before being joined at the meter itself, but I did not think this would be problematic?
AC cable run is 60m long and now has a total csa of 20mm due to two cables being utilised. This is adequate when run through Sunny Design.
So we are very confused.
Thanks in advance.

 

[Earthstore]

Just a thought, if the incoming voltage is high, IE 245-250 volts, then with voltage drop over that length of cable when both inverters are running near maximum then it will put them over voltage and trip out, and it will go from one inverter to the other, IE; as one kicks in it will trip the other out and then visa versa, also are they set for the UK, as this is another common problem.
Just a thought, aren't those inverters a little on the small side for a 9.6 KWP system? 3800x2= 7600, but that is their maximum output, they would probably run constantly at slightly less.
If it was installed on one phase then it should be G59 aswell.
I hope this helps.

 

[sedgy34]

Earthstore is correct about the over voltage they aren't undersized to sunny design either

 

[fiardor]

Just a thought, if the incoming voltage is high, IE 245-250 volts, then with voltage drop over that length of cable when both inverters are running near maximum then it will put them over voltage and trip out, and it will go from one inverter to the other, IE; as one kicks in it will trip the other out and then visa versa, also are they set for the UK, as this is another common problem.
Just a thought, aren't those inverters a little on the small side for a 9.6 KWP system? 3800x2= 7600, but that is their maximum output, they would probably run constantly at slightly less.
If it was installed on one phase then it should be G59 aswell.
I hope this helps.

Any idea how to overcome this phenomenon Earth?

My company has a similar problem going on so am anxious to hear of any solutions to rectify this scenario.

 

[sedgy34]

I will have to come back to you on this one
Have you tried 1 inverter first then introduce the other string by string

 

[Earthstore]

Have you calculated the voltage drop for that lengh of cable?
Even if your % is low, it may still be high enough to send them overvoltage if the incoming voltage is on the high side.
Even though I am not a fan of long DC runs because of saftey issues, if you moved the inverters close to the supply and kept your AC run short this would overcome the AC voltage drop, and as your DC is high voltage the voltage drop should be minimal.
I must point out that I am not a sparky, so I hope this makes sense and will help.

 

[TJLinks]

does anyone know how many volts an inverter adds to the grid voltage inorder to overcome the incoming voltage? is it a set voltage or is it a percentage of whatever the grid voltage is

 

[BruceB]

It is the current times the resistance of the cable(s) to the service head.

 

[Blueflash]

If I dont get this job sorted out my boss is gonna be quite unhappy!
These inverters (2 of) have an AC range of 180vac-265vac. The customers unconnected supply is running high at 250vac, but could two inverters side by side increase the total system voltage to over 265vac (or close). Enough for one inverter to stop running and go to "waiting" mode??
I dont know?

 

[Earthstore]

As I posted, it is probably because of the voltage loss in the AC cable to the inverters, remember though it is not the loss to the inverter but the loss from the inverter to the supply.
Why not just get some 35mm SWA and run it tempory along the ground for a couple of days to see if it cures the problem, if it is safe to do so for that installation of course.

 

[fiardor]

If they are sunny boys have you set inverter parameters to G59?

We have exactly the same problem going on and have had to reduce panels so that the voltage stays below the DNO threshold they have set for the area we are in. (253v)

SB4000TL 1= 9+8 panels
SB4000TL 2= 8+8 panels

We were initially using the customers 90 meter 10mm swa to run the inverters but have since changed to a dedicated 90m 16mm swa instead.
However this hasnt changed the situation and when the inverters are running up to near maximum the line voltage raises to over 262v and then we have a merry go round of inverter 1 on while inverter 2 goes into stand by until it kicks in then inverter 1 goes into stand by.
We have reduced the voltage to below 253v by running the system at 75% (24 instead of 33 panels)

We are currently waiting for a grid guard code from sma to change parameters of inverters to G59 but i dont think this will rectify the situation.

The voltage drop for a 16mm swa is within the required limits for this installation so am reluctant to ask my boss to instal another armoured twice the size of the old one and it still may not resolve this situation.

Hopefully will let you know how we resolve situation.

The most likely outcome is that we will have to remove 9 panels and refund.


The problem you have is the same as us, the customers supply voltage is too high but not over 253v so the DNO does not need to reduce the voltage. Dont want to put a downer on it all as i could be wrong but just teeing you up.

 

[Blueflash]

If they are sunny boys have you set inverter parameters to G59?

We have exactly the same problem going on and have had to reduce panels so that the voltage stays below the DNO threshold they have set for the area we are in. (253v)

SB4000TL 1= 9+8 panels
SB4000TL 2= 8+8 panels

We were initially using the customers 90 meter 10mm swa to run the inverters but have since changed to a dedicated 90m 16mm swa instead.
However this hasnt changed the situation and when the inverters are running up to near maximum the line voltage raises to over 262v and then we have a merry go round of inverter 1 on while inverter 2 goes into stand by until it kicks in then inverter 1 goes into stand by.
We have reduced the voltage to below 253v by running the system at 75% (24 instead of 33 panels)

We are currently waiting for a grid guard code from sma to change parameters of inverters to G59 but i dont think this will rectify the situation.

The voltage drop for a 16mm swa is within the required limits for this installation so am reluctant to ask my boss to instal another armoured twice the size of the old one and it still may not resolve this situation.

Hopefully will let you know how we resolve situation.

The most likely outcome is that we will have to remove 9 panels and refund.


The problem you have is the same as us, the customers supply voltage is too high but not over 253v so the DNO does not need to reduce the voltage. Dont want to put a downer on it all as i could be wrong but just teeing you up.

Thanks for that, it would make some sense of this frustrating saga! Picture and installation looks nice, but are you not using two off-grid inverters in the picture?? Blueflash

 

[fiardor]

Err what bud?

SB4000TL-20 x2
what makes you think that they are off grid?

 

[Blueflash]

Err what bud?

SB4000TL-20 x2
what makes you think that they are off grid?

Hiya fiardor,
Yellow casings are usually on the SMA Sunny Island inverters are they not? All our Sunny Boy inverters have been with Red casings, apart from when we get a Tri-power in which has a blue casing.

 

[TJLinks]

We had a few yellow SMAs from Segen........Just a different case colour