solutions are combined to get the best possible effect in the fuse failure supervisionfunction (SDDRFUF).SDDRFUF function built into the IED products can operate on the basis of external binarysignals from the miniature circuit breaker or from the line disconnector. The first caseinfluences the operation of all voltage-dependent functions while the second one does notaffect the impedance measuring functions.The negative sequence detection algorithm, based on the negative-sequence measuringquantities, a high value of voltage 3V2 without the presence of the negative-sequencecurrent 3I2, is recommended for use in isolated or high-impedance grounded networks.The zero sequence detection algorithm, based on the zero sequence measuring quantities,a high value of voltage 3V0 without the presence of the residual current 3I0, isrecommended for use in directly or low impedance grounded networks. In cases where theline can have a weak-infeed of zero sequence current 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.10.2.3 Setting guidelines10.2.3.1 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 longer 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, VBase and IBase respectively. Set VBase tothe primary rated phase-phase voltage of the potential voltage transformer and IBase tothe primary rated current of the current transformer.10.2.3.2 Setting of common parametersGlobalBaseSel: Selects the global base value group used by the function to define (IBase),(VBase) and (SBase).1MRK 506 334-UUS A Section 10Secondary system supervision277Application manual
