Beijing Quartet CSC-281 digital line protection and monitoring device functions: 1) over-current protection. Device is equipped with three-stage definite time overcurrent (optional direction, the composite voltage lockout) elements, anti-time protection components. 2) zero-sequence overcurrent protection. Device equipped with components, inverse element three-zero sequence definite time overcurrent. 3) Overload protection. Overload warning by the delay elements of the device, and investment return overload trip function. 4) three-phase reclosing function. Coincides with a protective boot does not correspond to start overlap between the two methods. 5) Closing accelerating protection. It means having phase current and zero-sequence current accelerating element can be achieved before the charging hands to accelerate and protect acceleration, after acceleration. 6) Small current grounding line function. Means having a small current grounding line device, with the monitor master station together constitute a centralized small current grounding line system can also be independently selected from the line, with the jump line selection function. 7) low cycle load shedding protection. Device has a low cycle load shedding components may be no flow and slip lock. 8) voltage load shedding protection. Device has a voltage load shedding element may be slippery voltage lockout. 9) FC lockout. FC lockout means having to work with an external fuse.