Photovoltaic (PV) arc-faults can lead to fires, damage property, and threaten the safety of building occupants. In response, Article 690.11 was approved for the 2011 National Electrical Code®, requiring new PV systems, 80 V or greater, on or penetrating a building to include a listed arc-fault protection device to extinguish series arc-faults. Currently, a number of manufacturers are developing arc-fault circuit interrupters (AFCIs) which detect arcing and de-energize the PV circuit. Sandia National Labs has undertaken a major effort to identify detection difficulties to ensure AFCIs robustly detect arcing conditions while avoiding false trips from noise sources.
These photographs show damage from PV arc-faults.
Sandia National Labs’ arc-fault detection and mitigation program is focused on making photovoltaic systems safer, more reliable, and bankable. Rare but high profile fires have given the PV industry a black-eye—tarnishing the view of PV as a clean, safe energy source. Arc-fault circuit interrupters minimize series arc-fault hazards, reduce operations and maintenance costs, and improve PV system bankability by reducing uncertainty in PV plant downtime.
Some of the areas the arc-fault detection and mitigation program is focused include:
- Developing a consensus arc-fault detector and circuit interrupter test plan.
- Collaborating with industry to test arc-fault detector prototypes.
- Characterizing arc-fault signatures and propagation in PV systems.
- Testing the reliability of AFCIs and assessing the risk of nuisance tripping from inverter noise, DC disconnects, and RF coupling.
- Working with Solar ABCs and code-making bodies to create clear, safety-focused requirements and robust AFCI test procedures.
- Collaborating with module, inverter, and BOS manufacturers to create arc-resistant components.
- Creating thermo-electrical simulations of arc events to quantify arcing and fire dangers.
- Investigating prognostics and health management of PV systems to measure PV degradation, prescribe maintenance schedules, and warn of arc-fault events.
- Investigating the pros/cons of module-level, string-level, and array-level arc-fault detection schemes.
- Testing techniques for locating the arc-fault and identifying faulty PV components.
To fill the new arc-fault circuit interrupter (AFCI) market, inverter, DC/DC converter, smart combiner box, microinverter, and circuit interrupter manufacturers are working to develop, test, and list detection and interruption devices according to UL Subject 1699B.
Sandia National Laboratories is currently working with multiple companies to develop commercial arc-fault detectors (AFDs) and looks forward to collaborating with additional manufacturers to create robust AFDs to improve the safety of US PV installations. The SNL facilities are ideal for testing the robustness of AFDs and AFCIs because the Distributed Energy Technologies Laboratory (DETL) contains reconfigurable PV arrays with a diverse portfolio of PV technologies, ages, and I-V characteristics, along with a range of connectors, DC disconnects, combiner boxes, DC line lengths, and inverters. Further, Sandia has world-renowned expertise in photovoltaic systems, RF noise characterization, and microelectronics and device reliability. This extensive knowledge base is leveraged to assist commercial manufacturers develop and test arc-fault detectors and circuit interrupters.
Specifically, Sandia has assisted AFCI manufacturers develop robust arc-fault detection algorithms by:
- Performing arcing tests at DETL with AFD prototypes to verify their functionality on PV strings with different of PV technologies, inverters, and balance-of-system (BOS) components.
- Assisting manufacturers calibrate the arc-fault detector algorithms by providing high-fidelity current and voltage signatures of arcing, baseline (non-arcing), DC disconnect switching, and inverter noise.
- Investigating PV system noise sources and suggesting robust arc-detection algorithms which avoid noisy bandwidths.
- Performing arc-fault finite-element thermo-electro-mechanical simulations of arcing events to determine arcing characteristics and burn times.
Sandia is currently testing arc-fault detectors and circuit interrupters for robust, nuisance-trip-free functionality. The goal of the program is to identify a series of tests that can be incorporated into test plan to insure AFCI functionality. The test plan is intended to be consensus-based, so Sandia is looking for participation from AFCI manufacturers, NRTL partners, and code-making body participants to identify the set of tests which insures robust arc-fault detection and circuit de-energization. If you would like to be included in the discussions please contact Jay Johnson (jjohns2 at sandia.gov, 505-284-9586).
For additional information on the Sandia National Laboratories arc-fault detection and mitigation program or to collaborate with the Sandia team, please contact Jay Johnson (jjohns2 at sandia.gov, 505-284-9586).