5-62 L90 Line Current Differential System GE Multilin5.4 SYSTEM SETUP 5 SETTINGS5It is possible to select the sum of all CT combinations. The first channel displayed is the CT to which all others will bereferred. For example, the selection “F1+F5” indicates the sum of each phase from channels “F1” and “F5”, scaled towhichever CT has the higher ratio. Selecting “None” hides the associated actual values.The approach used to configure the AC sources consists of several steps; first step is to specify the information about eachCT and VT input. For CT inputs, this is the nominal primary and secondary current. For VTs, this is the connection type,ratio and nominal secondary voltage. Once the inputs have been specified, the configuration for each source is entered,including specifying which CTs will be summed together.User selection of AC parameters for comparator elements:CT/VT modules automatically calculate all current and voltage parameters from the available inputs. Users must select thespecific input parameters to be measured by every element in the relevant settings menu. The internal design of the ele-ment specifies which type of parameter to use and provides a setting for source selection. In elements where the parametermay be either fundamental or RMS magnitude, such as phase time overcurrent, two settings are provided. One settingspecifies the source, the second setting selects between fundamental phasor and RMS.AC input actual values:The calculated parameters associated with the configured voltage and current inputs are displayed in the current and volt-age sections of actual values. Only the phasor quantities associated with the actual AC physical input channels will be dis-played here. All parameters contained within a configured source are displayed in the sources section of the actual values.DISTURBANCE DETECTORS (INTERNAL):The disturbance detector (ANSI 50DD) element is a sensitive current disturbance detector that detects any disturbance onthe protected system. The 50DD function is intended for use in conjunction with measuring elements, blocking of currentbased elements (to prevent maloperation as a result of the wrong settings), and starting oscillography data capture. A dis-turbance detector is provided for each source.The 50DD function responds to the changes in magnitude of the sequence currents. The disturbance detector schemelogic is as follows:Figure 5–13: DISTURBANCE DETECTOR LOGIC DIAGRAMThe disturbance detector responds to the change in currents of twice the current cut-off level. The default cut-off thresholdis 0.02 pu; thus by default the disturbance detector responds to a change of 0.04 pu. The metering sensitivity setting (PROD-UCT SETUP ÖØ DISPLAY PROPERTIES ÖØ CURRENT CUT-OFF LEVEL) controls the sensitivity of the disturbance detectoraccordingly.827092A3.CDRSOURCE 1CURRENT PHASORPRODUCT SETUP/DISPLAYPROPERTIES/CURRENTCUT-OFF LEVELPRODUCT SETUP/DISPLAYPROPERTIES/CURRENTCUT-OFF LEVELPRODUCT SETUP/DISPLAYPROPERTIES/CURRENTCUT-OFF LEVELSOURCE 2CURRENT PHASORSOURCE 6CURRENT PHASORACTUALSETTINGSETTINGSETTINGACTUALACTUALFLEXLOGIC OPERANDFLEXLOGIC OPERANDFLEXLOGIC OPERANDI_1I_1I_1SRC 1 50DD OPSRC 2 50DD OPSRC 6 50DD OPI_2I_2I_2I_0I_0I_0ORORORWhere ’ is 2 cycles oldIWhere ’ is 2 cycles oldIWhere ’ is 2 cycles oldII I_1 - _1’ >2*CUT-OFFI I_1 - _1’ >2*CUT-OFFI I_1 - _1’ >2*CUT-OFFI I_2 - _2’ >2*CUT-OFFI I_2 - _2’ >2*CUT-OFFI I_2 - _2’ >2*CUT-OFFI I_0 - _0’ >2*CUT-OFFI I_0 - _0’ >2*CUT-OFFI I_0 - _0’ >2*CUT-OFF
