PV system output circuit ferrite core applicability


#1

Greetings,

I am hoping to determine the best ferrite core applicability for the purposes of filtering out electrical noise between an electrical combiner panel where AC PV source circuits and microinverter monitor land, and the panel whence the output circuit ties into the grid-tied panel.

An Enphase (microinverters) technical representative suggested the following product:
https://www.digikey.com/products/en?vendor=0&keywords=Epcos+B64290L0082X087

In particular, I am interested in applicability of similar products given the following considerations:

  • Differing voltage or output ampacity characteristics from the output circuit
  • Differing physical dimensions of applicable ferrite cores; I am looking at this from an NEC perspective, where a 40% conduit fill factor is not to be exceeded (which would be for the product previously referenced for larger system sizes).

Suggestions and help is greatly appreciated- thank you!


#2

@SunSense The intended usage of the parts in question is not entirely clear; I understand at an overall level that you’re interested in suppressing conducted electrical noise between a solar power installation and a grid tie point, but there are details missing regarding the precise nature of how you intend to use them and the specific problem(s) that you’re trying to solve.

Would you be willing to share your dialogue with the Enphase personnel and/or any related support materials that you’ve referenced that are leading you to consider these products? I believe this would help me understand your problem and its context most easily.


#3

Hi Rick,

Thank you for the response. After further review of the Enphase technical brief (https://enphase.com/sites/default/files/downloads/support/PLC-Troubleshooting-EN-UK_0.pdf), as well as further dialogue with colleagues & another Enphase rep, it seems like the ferrite core referenced earlier is applicable for the majority of applications we would be using. Pages 2 & 5 show good schematics for our application. For larger conductors, where wrapping around the core isn’t physically feasible, in-line filters are recommended.

Any further insight would be appreciated, though!


#4

Adding the suggested cores to individual lines as suggested in the linked document would have the effect of adding inductance to the line, which should help reduce the conducted coupling of high-frequency noise between the two domains.

This said, if using the suggested cores I’d advise using only a single pass through; given the amount of 60 Hz current that’s likely passing through those conductors, the cores would likely become saturated and loose their filtering effectiveness if a higher turn count is used. Additionally, the material from which the suggested cores are made are of a type designed to be low-loss in the 100 kHz frequency band that’s of interest to you; if the objective is to suppress noise a high-loss material would seem to be preferable. It’s entirely possible that I’ve misinterpreted something, but offhand I’d be inclined to look at a product more along the lines of our P/N 240-2281-ND for use in the manner indicated.

I would also point out that we do have quite a few listings for higher-current line filters here, which may also be of interest to you.