A Spark of Light in Solar Inverter Testing ...

Serial arcing in PV systems occurs due to contact problems, e.g., faulty solder joints in the module or in the DC wiring of the inverter. In a worst case scenario the high temperatures at faulty contact points can cause the system to catch fire.

Arc fault detectors (AFD) in inverters take advantage of the fact that the arc leads to a current jump in the inverter or a characteristic broadband noise: They detect the arc and switch off before a critical energy is reached. These detectors have been mandatory for newly installed PV systems in the U.S. since 2011. "National and international studies have shown that arcing occurs very rarely in PV systems with a high-quality installation. Nonetheless, manufacturers in the European market offer arc detectors on a voluntary basis. Some building insurers have insisted on these detectors for fire protection reasons," explains Felix Kulenkampff from Fraunhofer ISE, who developed the new IEC standard in a standardization committee together with representatives from industry, testing companies and research. The new IEC standard eliminates some of the weaknesses of the old US standard, which did not simulate real operation sufficiently. As a result, many arcs went undetected, because they did not reach the alarm threshold values or because false alarms were triggered.

"A realistic test setup can significantly reduce the risk of undetected arcs and false tripping. In the test, it should be possible to ignite the arc as realistically as possible and under repeatable conditions," explains Felix Kulenkampff. For the test according to IEC standard 63027 (whose basic parameters match the revised US standard UL 1699B), an electronic DC source is used as a PV simulator instead of real PV modules. Current flows from the PV simulator into the inverter through a connection point that can be precisely disconnected. The connection point is a ball-and-socket joint made up of two tungsten electrodes, which are pulled apart at a defined speed, thus igniting a characteristic arc. Fixed test parameters (electrode distance and speed) can be stored and selected for the test sequence. To ensure that the measurement result is not influenced by the PV simulator, a filter network is connected between the inverter and the simulated PV system.