SMA SUNNY STRING-MONITOR Technical Description page 49

SMA Solar Technology AG 8 Function of the String Current Monitoring
Error sum
The error sum is a measure of the sensitivity of the string current monitoring. It can be parameterized
via the tripping time and tolerance, and is described by the following formula:
Comparison
Every 5 minutes, the Sunny Central Control compares the string current with the reference value for
the group. When the string current is outside the tolerance limits, Sunny Central Control records the
deviation. When the deviation exceeds the error sum, the Sunny Central Control displays the "SMU"
warning.
If the deviation is smaller than the error sum, the Sunny Central Control records the deviation. If a
deviation between the string current and the reference value persists, the deviations are recorded. As
soon as the deviations exceed the error sum, the Sunny Central Control displays the "SMU" warning.
The submenu "SMUs...Failure" shows which Sunny String-Monitor and which measuring channels
deviate too much from the group mean value. Upon confirmation at the Sunny Central Control, the
error sum is reset, and the warning disappears from the display.
With the flexible parameterization, the Sunny String-Monitor can detect the complete failure of a
string within one polling interval. Slightly elevated string currents are reliably detected in several
polling intervals and distinguished from typical current fluctuations of the PV array.
Technical Description SSM-TEN103132 49