The DC fault of the PV system is the biggest security risk of the power...

The exact extract asks which Huawei technology proactively shuts down the DC system to prevent a PV DC-side fault from spreading. The correct answer is D. Smart string disconnection. Fire suppression is a reactive measure after a fire starts, not the proactive DC-side electrical isolation mechanism. Smart terminal temperature monitoring may help identify abnormal heat, but it is not the technology that shuts down faulty PV strings. MPPT insulation monitoring can detect insulation abnormalities, but the named Huawei active shutdown technology is Smart String-Level Disconnection, or SSLD. Huawei describes SSLD as identifying DC-side faults such as reverse polarity, backflow current, and short circuits, then implementing automatic string-level shutdown on a millisecond basis. This prevents fault expansion and improves active safety at PV plants. Therefore, the extract points directly to smart string disconnection. References: Huawei SSLD and utility Smart PV safety documents.