Fault finding in a 1 MW photovoltaic plant by reflectometry

Time domain reflectometry has been used for diagnostic monitoring of a large size photovoltaic (PV) giant in operating conditions. By analysing the waveforms obtained when a step-voltage excitation is propagated down the electrical line connecting the PV generators to the inverter, we were able to detect, identify and localise the most common fault conditions, such as breaks of the circuit, insulation defects, wiring anomalies. Best compromise between analysis time and precision was achieved by testing groups of three paralleled strings (panels): in this way we were able to detect in a short time whether a fault was present, while its position was separately determined with a good precision by repeating the test on the single strings. The whole 1 MW PV plant was tested in a couple of days. Finally, we discuss some economical aspects of this fault finding technique.