Arc-Fault Circuit Interrupter (AFCI)
PV systems that are built according to today's installation standards and with high-quality components are generally very safe. Nevertheless, in rare cases, faulty contact points in the cabling of the PV module or the installation on the DC circuit can cause electric arcs, which can damage both the system and the building.
When a PV inverter with an integrated arc-fault circuit interrupter (AFCI) is used, a serial electric arc in the PV array is detected soon enough and extinguished by an interruption of the current.
If an electric arc occurs in the DC installation of a PV system during feed-in operation, this causes a change in the current and a typical interference spectrum. In this case, high-frequency portions are superimposed upon the normal operating current. These two criteria are the basis for detecting an electric arc reliably.
When the arc-fault circuit interrupter (AFCI) is enabled in the inverter, the PV array is monitored for electric arcs since they pose a risk of fire with larger currents. If a current phenomenon that is typical for electric arcs occurs (e.g. change in current, high-frequency portions), an electric arc is detected and the inverter immediately terminates the feed-in operation and reports this event. This event is reported via the user interface of the inverter or a superordinate communication device and Sunny Portal. Stopping the feed-in operation interrupts the current flow on the DC circuit and extinguishes the electric arc.
A detected electric arc causes the inverter to interrupt feed-in operation. To restart feed-in operation, the operational disruption which has occurred, must be reset through a manual restart. Alternatively, the arc-fault circuit interrupter can be activated without inhibiting operation. Depending on the country data set, arc fault detection is activated or deactivated by default. If the installation conditions permit this, you can change the default setting.
The following table contains an overview of the PV inverters for the commercial sector equipped with an arc-fault circuit interrupter.
Inverter | Device type |
|---|---|
Sunny Tripower X 25 | STP 12-50 STP 15-50 STP 20-50 STP 25-50 |
Sunny Tripower X 60 | STP 50-80 STP 60-80 |
Sunny Tripower 125 | STP125-70 |
Operating modes of the arc-fault circuit interrupter
Automatic restart:
The feed-in operation of the inverter is interrupted when an electric arc is detected, however the inverter resumes feed-in operation automatically. Yield losses can thus be avoided. Nevertheless, it is recommended to have the PV array checked by a qualified person after a fault has been reported.
Manual restart:
The feed-in operation of the inverter is interrupted when an electric arc is detected and the inverter goes into operation inhibition. The operation inhibition must actively be reset by the system operator so that the inverter resumes operation.
Manual restart after 5 AFCI detections:
The feed-in operation of the inverter is interrupted when 5 electric arcs are detected within 24 hours and the inverter goes into operation inhibition. The operation inhibition must actively be reset by the system operator so that the inverter resumes operation.
Additional information on the configuration as well as approvals and normative specifications can be found under the following link: Technical Information "Arc-fault circuit interrupter" and at www.SMA-Solar.com.