CT Power Offset on EG4 18Kvp

[sabues]

Hi folks,
I'm looking for an authoritative answer about what the CT Power Offset (W) setting does on my inverter and what modes of operation would have an effect on.



background: I recently installed this inverter as a whole home backup via feeder tap, and I'm trying to minimize the unwanted power export which occurs when there's sudden changes in PV generation. It's not much, usually short spikes of ~200w, but my POCO already called my attention as I don't have a net metering agreement in place (and would like to avoid it).
I was hoping CT Power Offset setting could help in this regards based on its name, if not, I would like to know what it does anyways as it's not documented in the manual.
I appreciate your input!

 

[ChrisG]

Curious minds want to know. I think some have solved this issue of power going past the CTs.

 

[sabues]

Thanks Chris, I'm doing some testing and observation before inquiring specifically about the export issue. I was convinced the export spikes only occurred when the load was very low (< 200W) and PV was not generating, but then loaded the inverter with 450W for 24hs and the pattern changed. It no longer exported at night but It exported during the day when there was a big swing on PV power. Just FYI, I'm running only 5 panels for testing the system before putting up the "production" panels. The test panels are placed on a purposely bad location, to test shading, partial shading and north-oriented scenarios, so it now looks like the export under load occurs when the string goes below the MPPT minimum voltage , and then back up to higher levels. The upward transition appears to align with the export to grid situations. These two situations are self inflicted and probably will go away when the inverter has real load and real panels. Still, knowing if I can use CT Offset or any other parameter fine tune these eventual export scenarios for Zero Export would be great.

 

[SignatureSolarJess]

Hi! I've connected with EG4 and they have informed me that this setting is put in place to offset the sensitivity of CTs. Not all brands of CTs read accurately, and not all brands of CTs read correctly. If you know exactly how much resistance is causing the error on your CTs, you can offset that resistance on the lines by changing the offset amount.

 

[sabues]

Thanks Jess,
I've been playing with this setting from the default value of -40W all the way from 400, 40, 20, 0 and -20, it looks like -20W is the setting with less export of all. I had to disconnect from the grid now until my Standard Interconnect Agreement with my Power Company goes through, but I will continue to experiment with this value when I connect my system back and I run on a more normal configuration with all the panels.
It worth noting that my load is the whole house, so the work of the CT should be very straight forward, there's no load in front of the inverter. If PV or Battery is supplying power to my load, then the CT current should be zero.

 

[Quattrohead]

Make sure all of your settings are off grid mode only. It will still lean on the grid if it has to due to overload or when the batteries are dangerously low.
In this mode it actually turns the grid relay off but still monitors the grid so there is absolutely no chance of feedback but it is synchronized with the grid so if it needs it in a hurry it can switch over.