measurement element will be used as sending criterion of the permissive input signalCSUR.In the overreaching alternative, an overreaching directional residual overcurrentmeasurement element will be used as sending criterion of the permissive input signalCSOR. Also the underreaching input signal CSUR can initiate sending.BLOCKCRPLTR_CRDBLKCSCRLOverreachCSORCSURTRIPCSen05000280_3_ansi.vsdANDAND ANDANDANDANDOROR025ms0-tCoord0050ms050msANSI05000280 V1 EN12.5.6.3 Unblocking schemeIn unblocking scheme, the lower dependability in permissive scheme is overcome byusing the loss of guard signal from the communication equipment to locally create areceive signal. It is common or suitable to use the function when older, less reliable, powerline carrier (PLC) communication is used.The unblocking function uses a guard signal CR_GUARD, which must always be present,even when no CR signal is received. The absence of the CR_GUARD signal for a timelonger than the setting tSecurity time is used as a CR signal, see figure 247. This alsoenables a permissive scheme to operate when the line fault blocks the signal transmission.The received signal created by the unblocking function is reset 150 ms after the securitytimer has elapsed. When that occurs an output signal LCG is activated for signalingpurpose. The unblocking function is reset 200 ms after that the guard signal is presentagain.1MRK 506 335-UUS A Section 12Scheme communication521Technical manual
