Arc Detector for Remote Detection of Dangerous Arcs on the DC Side of PV Plants

Abstract

DC arcs in PV plants with high DC voltage are much more dangerous than AC arcs, as there are no zero-crossings of current. Despite the still relatively small number of PV plants, such arcs have already caused quite a number of fires worldwide, causing expensive damage. In the early nineties such fires have occurred at several PV plants (e.g. Mont Soleil (560 kWp)). In spring 2006, a smouldering fire occurred in the connector box of an 11 years old PV plant in Burgdorf and a considerable number of arcs occurred in defective BP modules in many countries. Only with a lot of luck major damages at buildings did not happen. With the rapidly increasing number of PV plants and especially due to the increasing age of these plants the number of such events will probably increase considerably in the next years. Already in 1994 to 1998, at first in a national and then in an EU project in co-operation between BFH’s PV laboratory and Alpha Real, an arc detector was developed, which was successfully tested in several PV plants in Europe and USA [1], [2]. These devices were realised as stand-alone devices (with an integrated supply and an expensive electromechanical disconnecting switch). At many inverters additional filters were needed due to high RF emissions on the DC side. With the increased EMC quality of modern inverters also on the DC side, the detection of such arcs is now much easier, therefore such arc detectors can now be integrated directly into the inverter, reducing considerably the cost and at the same time making possible much more sophisticated detection strategies. Such an arc detector should be an integral part of a modern inverter in order to increase the long-term safety of a PV plant.