high value of voltage 3V2 without the presence of the negative-sequence current 3I2 is acondition that is related to a fuse failure event.The zero sequence detection algorithm, based on the zero sequence measuring quantitiesis recommended for use in directly or low impedance grounded networks: a high value ofvoltage 3V0 without the presence of the residual current 3I0 is a condition that is relatedto a fuse failure event. In cases where the line can have a weak-infeed of zero sequencecurrent this function shall be avoided.A criterion based on delta current and delta voltage measurements can be added to the fusefailure supervision function in order to detect a three phase fuse failure. This is beneficialfor example during three phase transformer switching.11.1.3 Setting guidelines11.1.3.1 GeneralThe negative and zero sequence voltages and currents always exist due to different non-symmetries in the primary system and differences in the current and voltage instrumenttransformers. The minimum value for the operation of the current and voltage measuringelements must always be set with a safety margin of 10 to 20%, depending on the systemoperating conditions.Pay special attention to the dissymmetry of the measuring quantities when the function isused on long untransposed lines, on multicircuit lines and so on.The settings of negative sequence, zero sequence and delta algorithm are in percent of thebase voltage and base current for the function. Common base IED values for primarycurrent (IBase), primary voltage (VBase) and primary power (SBase) are set in GlobalBase Values GBASVAL. The setting GlobalBaseSel is used to select a particularGBASVAL and used its base values.11.1.3.2 Setting of common parametersSet the operation mode selector Operation to Enabled to release the fuse failure function.The voltage threshold VPPU is used to identify low voltage condition in the system. SetVPPU 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 always setSealIn to Enabled since this will secure a fuse failure indication at persistent fuse fail whenclosing the local breaker when the line is already energized from the other end. When theremote breaker closes the voltage will return except in the phase that has a persistent fusefail. Since the local breaker is open there is no current and the dead phase indication willSection 11 1MRK 505 337-UUS -Secondary system supervision274Application manual
