the local breaker is open there is no current and the dead phase indication will persist in thephase with the blown fuse. When the local breaker closes the current will start to flow and thefunction detects the fuse failure situation. But due to the 200 ms drop off timer the outputBLKZ will not be activated until after 200 ms. This means that distance functions are notblocked and due to the “no voltage but current” situation might issue a trip.The operation mode selectorOpMode has been introduced for better adaptation to systemrequirements. The mode selector enables selecting interactions between the negativesequence and zero sequence algorithm. In normal applications, theOpMode is set to eitherUNsINs for selecting negative sequence algorithm orUZsIZs for zero sequence basedalgorithm. If system studies or field experiences shows that there is a risk that the fuse failurefunction will not be activated due to the system conditions, the dependability of the fusefailure function can be increased if theOpMode is set toUZsIZs OR UNsINs orOptimZsNs. InmodeUZsIZs OR UNsINs both negative and zero sequence based algorithms are activated andworking in an OR-condition. Also in modeOptimZsNs both negative and zero sequencealgorithms are activated and the one that has the highest magnitude of measured negative orzero sequence current will operate. If there is a requirement to increase the security of the fusefailure functionOpMode can be selected toUZsIZs AND UNsINs which gives that both negativeand zero sequence algorithms are activated and working in an AND-condition, that is, bothalgorithms must give condition for block in order to activate the output signals BLKU or BLKZ.9.2.3.3 Negative sequence based M13683-17 v9The relay setting value3U2> is given in percentage of the base voltageUBase and should notbe set lower than the value that is calculated according to equation 86.1003223 UBaseUUEQUATION1519 V5 EN-US (Equation 86)where:U2 is the maximal negative sequence voltage during normal operation conditions, plus a margin of10...20%UBase is the base voltage for the function according to the settingGlobalBaseSelThe setting of the current limit3I2< is in percentage of parameterIBase. The setting of3I2<must be higher than the normal unbalance current that might exist in the system and can becalculated according to equation 87.100223 IBaseIIEQUATION1520 V5 EN-US (Equation 87)where:I2 is the maximal negative sequence current during normal operating conditions, plus a margin of10...20%IBase is the base current for the function according to the settingGlobalBaseSel9.2.3.4 Zero sequence based M13683-43 v8The IED setting value3U0> is given in percentage of the base voltageUBase. The setting of3U0> should not be set lower than the value that is calculated according to equation 88.Section 9 1MRK 505 355-UEN ASecondary system supervision146Application manual
