14.2.3.2 Setting of common parameters M13683-9 v9Set the operation mode selector Operation to Enabled to release the fuse failurefunction.The voltage threshold VPPU is used to identify low voltage condition in the system.Set VPPU below the minimum operating voltage that might occur during emergencyconditions. We propose a setting of approximately 70% of VBase.The drop off time of 200 ms for dead phase detection makes it recommended to alwaysset SealIn to Enabled since this will secure a fuse failure indication at persistent fusefail when closing the local breaker when the line is already energized from the otherend. When the remote breaker closes the voltage will return except in the phase thathas 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.14.2.3.3 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 497.Section 14 1MRK 504 163-UUS ASecondary system supervision670 Transformer protection RET670 2.2 ANSIApplication manual
