Fault analysis in solar photovoltaic (PV) arrays is a fundamental task to protect PV modules from damage and to eliminate risks of safety hazards. This paper focuses on line-line faults in PV arrays that may be caused by short-circuit faults or double ground faults. The effect on fault current from a maximum-power-point tracking of a PV inverter is discussed and shown to, at times, prevent overcurrent protection devices (OCPDs) to operate properly. Furthermore, fault behavior of PV arrays is highly related to the fault location, fault impedance, irradiance level, and use of blocking diodes. Particularly, this paper examines the challenges to OCPD in a PV array brought by unique faults: One is a fault that occurs under low-irradiance conditions, and the other is a fault that occurs at night and evolves during “night-to-day” transition. In both circumstances, the faults might remain hidden in the PV system, no matter how irradiance changes afterward. These unique faults may subsequently lead to unexpected safety hazards, reduced system efficiency, and reduced reliability. A small-scale experimental PV system has been developed to further validate the conclusions.

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Solar photovoltaic (PV) arrays behave distinctively from conventional power sources so that they need special consideration in fault analysis and protection. The faults inside PV arrays usually cause overcurrent that may damage PV components. This paper focuses on the challenges to overcurrent protection devices (OCPDs) in a PV array under two types of unique fault scenarios. One is a line-line fault that occurs under low irradiance conditions. In this circumstance, the fault current may not be large enough to trip the OCPDs in the PV array, even when high irradiance occurs later in the day. The other fault scenario is that when PV blocking diodes are used in the PV array, the reverse current may be greatly limited. However, OCPDs might not detect the reverse current properly. In both fault scenarios, the fault may not be cleared successfully by conventional OCPDs. Therefore, faults may remain undetected, which could lead to reduced system efficiency, reduced system reliability, and even unexpected safety hazards.