Beijing Quartet CSC-211 digital line protection and monitoring device 1) over-current protection. Device equipped with components, low-voltage components, phase current directional element and inverse-time three-stage definite time overcurrent element. Each segment can have a low voltage element selective inputs and direction component, overcurrent Ⅲ segment can be set as inverse-time characteristics. 2) zero-sequence overcurrent protection. Device equipped with components, zero-sequence directional element and inverse elements Three-zero sequence definite time overcurrent. Each segment may have selectively invested directional elements and zero sequence Ⅲ segment can be set as inverse-time characteristics. 3) Small current grounding line function. Means may constitute the main station centralized small current grounding line system, sent by the master on each computing device signal determining ground; but also with a ground single criterion means, to achieve local sentenced ground. 4) Overload protection. Overload element device operable to trip or alarm. 5) three-phase reclosing function. Device has asynchronous (not the subject no pressure do not check the same period), check the same period, the prosecution no pressure, no pressure check and check-year (check no pressure or check-year) closing mode. 6) 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. 7) low cycle load shedding protection. Device able to distinguish the system frequency from normal to low frequency fault conditions, the motor reverse charging and real active shortfall and achieve low cycle load shedding. 8) Low splitting protection. Devices can automatically determine whether removal system voltage from the normal state to a low-voltage load, low voltage splitting. 9) Other functional descriptions. PT disconnection device having an alarm control mother and spring break warning alarm feature is not charged.