Energy Products

CT (Current Transformer) Orientation

I realize i'm never going to get a technical answer from customer service about this question, and I'm 100% someone has come across this before.

The Powerwall documentation is explicit in details on CT orientation.

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Appendix E:
Ensure that:
-Site CT's are positive for import, negative for export.
-Solar CT's are positive when PV array is producing power (Solar is NEVER negative during daytime).

Negative power flow may indicate CT is installed on the wrong PHASE!
-If the "toward source" CT label is correctly facing the solar inverter but power flow is negative, a voltage-current mismatch is likely.
-Physically move the CT to the correct phase with the label facing the correct direction. Do not use the Flip checkbox in this case.

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Now in my case, the Powerwall was not charging, CS saw negative output on the solar source. CS went ahead and flipped the negative value and my Powerwall started to charge but my solar output immediately went from 8.1 kW to 4.5 kW. Overall sum of the total system usage was immediately 55% of the pre-flipped values. If a CT was flipped, overall absolute sum should be the same. It seems now that there is a significant power factor change.

Forward in time a week, a Tech comes out for an unrelated issue, i bring up the flipped CT and he went ahead and checked. CT is actually installed in the correct orientation. Per the Tesla documentation, that leaves only 1 or 2 root causes.

1. CT is on the wrong phase
2. The phases in the BUG are reversed

The tech checked the wiring in both inverters as well as the BUG but wasn't 100% confident that the phasing was correct, escalated to a manager. I independently looked at the wiring and to me it looks correct.

My question is, would a CT installed on the incorrect phase (but in the correct orientation) cause the system to report a nearly 50% offset in generation?


Other sources:

https://www.kele.com/content/blog/2014/10/29/47-ways-to-wire-your-power-meter-wrong

https://forums.mikeholt.com/threads/ct-placement-and-phase-angle.50659/

Comments

  • The polarity of the CTs can be set by software also with the TEG in installer mode. The installer usually checks the Solar CTs during installation to make sure that the Solar is always producing and never consuming. Why do you see a 55% drop in your solar output?? I don’t really know. The Solar CTs would show a positive, negative or zero output. But not half...

    Now, the way that the TEG works is by applying the Kirchhoff’s law. The sum of all currents into a node is zero. Do you have tri-phase service or split phase? Are you commercial or residential?
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