High frequency error on making grid connection

Q&A and troubleshooting
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1

Have 3-phase grid connect system with 3 x Multiplus II with ESS & 2 x Fronius Primo on AC out, one on each of two phases and nothing on AC out of the third phase.

Works OK as off-grid 3-phase, but the moment the 3-phase grid circuit breaker is closed the Fronius inverters shut down with error 105 - AC frequency too high. This happens before the Multis have been able to synchonise to the input, so the Fronius inverters are actually still seeing the 50Hz supply from the Multis. However some noise must be passing through the Multi to trigger the 105 error. Updated Multis to latest firmware, but this made no difference. Any suggestions welcome.

2

Can you download a VE config file and upload it? There might some clues there. A good place to start.

3

The issue has now been resolved. Turns out that the pole fuse (that is, the fuse that protects the service line from the mains supply) on one of the phases was corroded, resulting in high impedance on the AC-in feed. MultiPlus & Primo settings were OK.

Something to keep in the back of our minds, in case it ever happens again.