Like any other electrical installation, photovoltaic systems are subject to electrical faults, including arc faults, short circuits, ground faults and reverse currents. These faults and other failures of the system, including cable insulation breakdowns, rupture of a module, and faulty connections, can mean that areas of the system overheat, which can then ignite combustible material in its vicinity – posing a threat to nearby project infrastructure, personnel and the surrounding environment. Wrongly installed or defective DC/AC inverters have also been the cause of several damaging photovoltaic fires.
In the worst-case scenario, faulty conditions on the photovoltaic system will not only result in overheating, but might also cause a DC arc. There are three kinds of DC arcs:
- Serial arcs: These occur when a connection is pulled apart while the PV is producing current. Typical reasons for serial arcs include loose connections or connector defects (e.g., in the soldered joints within the module). For this reason, special care should be taken when PV systems are isolated in a fire situation.
- Parallel arcs: These occur when insulation systems are damaged. Two conductors of opposite polarity in the same DC circuit are often run in close proximity to each other. The insulation between these two wires can become ineffective due to animals chewing on them, UV breakdown, embrittlement, cracking, moisture ingress and freeze / thaw cycles.
- Ground arcs: These arcs occur on ground cables and can be triggered by a fault in any one single insulation system.
Currently, there is no single solution for mitigating the risk of DC arcs. The first line of defence should be high quality components, effective installation and the use of protective devices for the entire electrical system on a PV plant.
However, reliable detection of arc faults is a severe challenge for the industry and when arcs are detected, determining an appropriate corrective action is often difficult. Arcs must be reliably detected, without causing false alarms that can affect the operation of the park.