Help me solve an inverter mystery...

[nwdiver]

A friend of mine has a 10kW SMA inverter. It trips on a 'DI Converter Fault' almost everyday at ~9:30am. Sometimes it's an hour or so earlier... sometimes a few hours later but it's almost always in the morning usually only once. For some reason a couple days ago it went ape sh*t and tripped several times more in the morning than it usually does. This has been an issue for the past ~4 years. We've tried improving the grounding, contacting SMA, contacting the local utility.... nothing. I doubt it's the inverter but we haven't really ruled that out. Nothing else in the house cares about what ever is causing the inverter to fault.

My hypothesis is it's his transformer(s). On his street there are 3 15kVA transformers in parallel on the 240v side so they form several loops with the HV side. I've never seen that before. I think it's possible that the parallel transformers are establishing some kind of weird resonance when load is juuuuust right in the mornings. This would explain how erratic the tripping events are. I'm hoping to try to convince the utility to isolate his transformer. Anyone with electrical experience think this is the issue? Has anyone seen parallel transformers before?

 

[ewoodrick]

From the SMA site

• All PV module arrays are designed in such a way that they have a parasitic capacitance against their environment, and this can rise further in the event of a moist surface (rain, dew). Under specific design or weather conditions, the PV array’s discharge capacity can rise so far that the resulting capacitive leakage current can interfere with the residual current monitoring of the inverter. To ensure that residual currents are always detected, the inverter interrupts feed-in operation as a precautionary measure and then automatically reconnects to the utility grid when normal values have been restored.

Sun coming up, air conditioners kicking on, dew burning off? Is it different in winter vs summer? Does the timing change between winter and summer? Are there any other solar systems on that feed?

 

[nwdiver]

From the SMA site

• All PV module arrays are designed in such a way that they have a parasitic capacitance against their environment, and this can rise further in the event of a moist surface (rain, dew). Under specific design or weather conditions, the PV array’s discharge capacity can rise so far that the resulting capacitive leakage current can interfere with the residual current monitoring of the inverter. To ensure that residual currents are always detected, the inverter interrupts feed-in operation as a precautionary measure and then automatically reconnects to the utility grid when normal values have been restored.

Sun coming up, air conditioners kicking on, dew burning off? Is it different in winter vs summer? Does the timing change between winter and summer? Are there any other solar systems on that feed?

No. We considered environmental factors like that but there's no correlation between the faults and weather. The system is in Andrews, TX. Super dry. Trips during dry weather, and during humid or wet weather. Also sometimes doesn't trip at all. I have several other systems in the area that do fine but not on this feed.