Fronius Symo 3.0-3-S Inverter Error 301: Overcurrent, AC Grid Issue, Troubleshooting & Service Cost

Hello, after the complete failure of the Fronius Symo 3.0-3-S inverter at the end of July and replacement by the service with a new one, a new problem appeared, namely the error 301. In the manual, he says:
Overcurrent (AC).
Behavior: Short-term interruption of feeding into the grid. The inverter restarts the system startup.
Troubleshooting: If the status message persists: Contact a service technician
trained by Fronius.

I contacted my installer, after three weeks, the gentlemen from the service called and said:
"They are ready to repair the inverter, the courier arrives, takes the inverter to the service and makes a diagnosis there, and everything would be great if not for the fact that, if Fronius does not find a fault, I will be charged for about 100 euros (transport and diagnostics).

In addition, they also sent possible reasons for the error
301 Current peak on the mains supply detected
What can cause:
1. Voltage drop on the public mains
2. Grid Impedance out of permitted values
3. Bad contact of the power stack with AC
4. Measuring error on the power stack

The problem is so bothersome that when the inverter catches an error, it is not able to restart itself, synchronize and start production, there must be physical interference disconnecting the inverter from the AC side for about 1-3 minutes and the problem disappears.
I have had the installation for a year earlier, except for the failure of the inverter, the problem never occurred.
Ad 3, the installation in the house with the connection is new.

The question of where to start to eliminate the problem?

Added after 19 [hours] 32 [minutes]:

Today I learned from an electrician to find a UPS x 3 for each phase, preferably APC, connect via USB or RS232 and start logging with the apcupsd program.

For me, the Fronius ig 60 hv once caught this error and reset itself, but it was only one time. If it does not restart itself, it is an internal error of the inverter, otherwise a defect.

Added after 4 [minutes]:

1. Voltage drop in the public supply network
2. Mains impedance outside the allowed values
3. Bad contact with the stack of AC
4. Measurement of error on the power stack
It will also happen when you use high-power receivers, the voltage drop for me popped up when welding with high current.

Well, I don't know myself, but thinking logically when the inverter catches an error (it finds that something is wrong with the network parameters), it should be restarted, start checking again and turn on. And for me it is not like that, I have to physically turn it off and it is just starting to work.
Best of all, I told my installer, he passed the information to Fronius and they said it was a symptom according to the procedure.
In my case, the error was caught 3 times twice, it was on Sunday around 12-13, so I did not have a heavy load on the network, only the boiler could work.
Added after 21 [minutes]:
On the Fronius website I downloaded the pdf manual and it says:

Code:
301

Description:
Overcurrent (AC)

Behavior:
Brief interruption of the mode
mains supply
The inverter starts over
system boot

Removal:
If the status message is displayed constantly: Contact the service technician
trained by Fronius.

Reasoning, it should reboot and reattach.

It was calm until today, beautiful sunshine 3:30 PM no production, I went to the inverter and it is in the process of synchronization, the test passed correctly, the production starts and suddenly it crashes error 112 error description in the manual is an RCMU error restart and error 301 again - overcurrent, I did a current restart of the inverter, it started up and by the end of the day it worked without problems.
I read that the inverter has RCMU in security, while looking on the Internet, I found that it is a module that works like a differential. I do not know if I understand it correctly, but it seems to me that these problems are not the fault of the inverter, but the network.

czarnu wrote:

I read that the inverter has RCMU in security, while looking on the Internet, I found that it is a module that works like a differential. I do not know if I understand it correctly, but it seems to me that these problems are not the fault of the inverter, but the network.

I agree with this line of reasoning.
Check:
- supply line impedance
- insulation resistance of the wires on the AC and DC side
- mains voltage at the time of the problem.

You should find these measurements in the installation commissioning report.

First, check the entire installation from the AC side. Inverters are very sensitive to poor contacts. Likewise, to be sure, you can perform the above-mentioned measurements to be sure.

I propose to leave this problem to the installer of the PV installation, you do not lose the warranty, they will find the cause and in the event of a mistake and shipping, you do not bear the costs because the installer pays Fronius for replacing the inverter.