Cause : LSU charging busbar fault comes when the DC voltage rise in 10 ms is not acceptable during charging. The level is below the value set in parameter 120.26 Maximum dU/dt, but DC voltage has not reached the level set in parameter 120.25 MCB closing level.

1. Check the connections of the DC capacitors in the power modules and parameters 120.25 MCB closing level and 120.26 Maximum dU/dt.
2. Check that the input voltage is stable during start.