Sunny Boy: Active power limit AC frequency

[Solarisium]

My Sunny bow 3.8 US-41 power takes a dive when grid frequency hits 60.04 Hz. see graphs below plotted using data from two different days.

This message is recorded in the event list: 507 Active power limit AC frequency.
Often times it is coupled with this message: 8006 String A is in derating mode.


SMA's KB for f8006:
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New Event Code 8006 with Firmware release 3.02.11.R for SBx.x-1SP-US-41
Aug 10, 2022•Knowledge​

Description:
Event 8006 is displayed in the inverter log.
Displayed text message is "String X (A, B or C) is in derating mode".


Explanation:
With release of FW version 3.02.11.R for SBx.x-1SP-US-41 a new event 8006 was introduced.
The event is triggered as soon as one of the three strings is not actively tracking the MPP voltage anymore.

Any limitation of the output power of the inverter is causing at least one string to get out of the MPP tracking mode.
Possible reasons:
- reaching the 10 A string current limit
- reaching of nominal power (nameplate of the inverter)
- high temperature
- power limitation due to grid condition, e.g. related to frequency
- power limitation via pv system control / set active power lmitation

Basically the inverter will derate at least one string (starting with the string with the lowest voltage).
The behavior is not new and not changed by FW update. Just the displaying of the event indicating such operating state is new.
Thus the installer may notice the "new" event but the general behavior of the inverter - if compared - is not different from the behavior before the update.
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Has anyone experienced any of these two messages? any solution?

 

[Solarisium]

Answering my own question:
After looking at some technical documents on SMA site (available when you login as an installer. See a screenshot attached), CA Rule 21 has a very tight range (0.04Hz in Rule 21, compare to 0.3 Hz in UL1741) of frequency for the upper limit. Once the grid frequency exceeds 60.04 (e.g., 60.041), the production curtails for some 20 to 30 minutes.
Today (March 27) the grid exceeded 60.04 Hz three times, causing lower production for a total of nearly one hour (seems like the inverter goes thru a ramp-up after detection of >60.04 Hz.

CA Rule 21 is in force for California and cannot be changed (unfortunately) .