SMA STP 50-40 - Activating and Setting String-Failure Detection

8 Operation
SMA Solar Technology AG
Operating manual STP50-4x-BE-en-23 85
Inverters with arc-fault circuit interrupter (AFCI) without operation inhibition should be monitored
regularly. Recurring electric arcs should promptly be inspected and rectified by qualified persons. If
it is not possible to inspect and rectify the fault immediately, the inverter should be decommissioned
until the cause of the fault has been clarified and rectified. Recurring electric arcs can damage the
connection cables and the system components. Failures can occur. Uncontrolled electric arcs can
also cause a fire.
Procedure for country data sets without year or with year < 2018:
• In the parameter group Device > Inverter, select the parameter AFCI switched on or
AfciIsOn and set to Yes, without permanent operation inhibition.
Procedure for country data sets with year ≥ 2018:
1. In the parameter group Device > Inverter, select the parameter AFCI switched on or
AfciIsOn and set to Yes.
2. In the parameter group AC Side > Operation > Manual restart, select the parameter After
arc fault detection or ManRstr.ManRstrAFCI and set it to Off. The parameter Activated
or ManRstr.IsOn can only be set to No if all parameters in the group Manual restart are
set to Off.
If the AFCI is configured without permanent operation inhibition, the system should be monitored
closely and recurring faults in the AFCI should be investigated immediately by qualified persons. If it
is not possible to identify the cause of the error, the inverter should be taken out of operation until
the investigation and corrective action can be completed. Recurring errors may cause damage to
neighboring conductors and system components, which could result in more extensive system
failures and damage and even to uncontrolled electric arcs and fires.
8.25 Activating and Setting String-Failure Detection
If you would like to use the string-failure detection, you will have to activate it.
You have the option of combining inputs with the same properties (e.g. shading, alignment or
module type) in a group. A total of 3 groups are available. At least 2 inputs must be assigned per
group.
You must set the sensitivity and tolerance for string-failure detection. You must also set the minimum
time for which the tolerance must be exceeded before the inverter reports an event.
You can also set the activation threshold for string-failure detection to avoid an erroneous event
message. In systems with a very inhomogeneous alignment of the PV modules, events of too low DC
voltage or too low DC current can occur relatively frequently. If you increase the activation
threshold, make sure that the string-failure detection only becomes active when there is sufficient DC
power. In this way, you avoid erroneous event messages under unfavorable irradiation conditions.
You can carry out the activation and setting of the string-failure detection via the device parameters
or using the installation assistant.
The activation threshold for the string-failure detection can only be set via the device parameters.
The activation threshold is set to 20% of the inverter's nominal power by default.