FC-F30/F22/F21 is a distribution automation terminal product developed for on-post switches. It is developed according to the latest development requirements of distribution network automation and absorbing new research results of computer technology, digital signal processing technology, and grid fault detection technology. A new type of feeder remote terminal equipment FTU. Its design, manufacturing and inspection adopt international IEC standards and relevant national standards. It is suitable for 10KV feeder monitoring and control. In addition to remote signaling, remote measurement and remote control functions, it also has the ability to capture fault signals (phase-to-phase short circuit, single-phase grounding, etc.), combined with primary switches (circuit breakers, load switches, reclosers, etc.), and communicate with the main station of the distribution district (Or with the cooperation of the power master station), it can complete the fault diagnosis of the 10KV feeder, the isolation of the faulty section, the network reconstruction and the normal power supply of the non-faulty section.