has a persistent fuse fail. Since the local breaker is open there is no current and thedead phase indication will persist in the phase with the blown fuse. When the localbreaker closes the current will start to flow and the function detects the fuse failuresituation. But due to the 200 ms drop off timer the output BLKZ will not be activateduntil after 200 ms. This means that distance functions are not blocked and due to the“no voltage but current” situation might issue a trip.The operation mode selector OpModeSel has been introduced for better adaptation tosystem requirements. The mode selector enables selecting interactions between thenegative sequence and zero sequence algorithm. In normal applications, theOpModeSel is set to either V2I2 for selecting negative sequence algorithm or V0I0 forzero sequence based algorithm. If system studies or field experiences shows that thereis a risk that the fuse failure function will not be activated due to the system conditions,the dependability of the fuse failure function can be increased if the OpModeSel is setto V0I0 OR V2I2 or OptimZsNs. In mode V0I0 OR V2I2 both negative and zerosequence based algorithms are activated and working in an OR-condition. Also inmode OptimZsNs both negative and zero sequence algorithms are activated and the onethat has the highest magnitude of measured negative or zero sequence current willoperate. If there is a requirement to increase the security of the fuse failure functionOpModeSel can be selected to V0I0 AND V2I2 which gives that both negative and zerosequence algorithms are activated and working in an AND-condition, that is, bothalgorithms must give condition for block in order to activate the output signals BLKVor BLKZ.11.1.3.3 Negative sequence based M13683-17 v9The relay setting value 3V2PU is given in percentage of the base voltage VBase andshould not be set lower than the value that is calculated according to equation 82.1003223 VBaseVPUVEQUATION1757-ANSI V4 EN-US (Equation 82)where:V2PU is the maximal negative sequence voltage during normal operation conditions, plus a margin of10...20%VBase is the base voltage for the function according to the settingGlobalBaseSelThe setting of the current limit 3I2PU is in percentage of parameter IBase. The settingof 3I2PU must be higher than the normal unbalance current that might exist in thesystem and can be calculated according to equation 83.1MRK 505 370-UUS A Section 11Secondary system supervisionBusbar protection REB670 2.2 ANSI 287Application manual
