SW 5548 dropping the grid
I have a pair of SW5548's in series stacked mode, providing 120/240. We were off-grid for almost 15 years, and brought in grid-power about 18 months ago. After some initial problems, traced to a missing jumper, both inverters would work in Sell mode -- powering the house from the grid, and switching seamlessly to inverting when they would drop the grid. By seamlessly I mean that computers remain powered up; the microwave clock continues to keep time; and we do not note the lights flickering.
The problem is that they are dropping the grid when the grid power is within specifications. They are doing this multiple times a day, and they are NOT dropping the grid at the same time.
I have measured the power quality at the AC1 input to the inverters using a Fluke 1735 power logger; and the power company also attached a logger recently to the meter during a time when the inverters dropped the grid multiple times, and no abnormalities were noted.
The units were purchased in 2000, initially with Revision 4.01 firmware; and were later updated to Rev 4.10 which made them compatible with UL1741 First Edition requirements. (And these were approved by my power company to operate in sell mode).
One person thought there might be AC Ripple on the DC input from the VCS-10 controller. Measurements with a Fluke Volt-Ohm meter (yes, I know, this will miss stuff but I don't have access to an oscilloscope) revealed no more than about 1.2VAC; no correlation with increased wind turbine output and grid drops; and also, the grid would still drop even with the wind turbine disconnected from the system.
If it was just a single inverter, I would be inclined to blame either that inverter or something connected to it. If both were dropping at the same time, I would be inclined to blame power quality, or possible a grounding issue. So, other than replacement with a different model inverter (big bucks) that has diagnostics, I'm not sure what to do.
Any thoughts on how to further troubleshoot would be much appreciated.
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