AST-411 digital transformer differential protection device is suitable for 35kV and below voltage substation the vols main transformer, as the transformer primary protection. Main functions: a) the differential speed off protection function: split-phase differential quick-break protection action time is less than 25ms; b) differential protection function: sub-phase differential protection (harmonic restraint, the ratio of the system dynamic characteristics of the low-pressure side of the CT ratio adjustment function); c) CT disconnection detection and differential current excessive alarm function: real-time detection of CT disconnection, locking differential protection, run-time when the poor can alarm flow more limited; d ) body protection function: the action of heavy gas regulator heavy gas action, light gas alarm, the regulator light gas alarm; e) start the ventilation function: When the high-pressure side of the B-phase current is greater than start the ventilation current setting to start the ventilation outlets; e ) event logging, fault recorder; g) CAN data communication functions.