CHAPTER 8: APPLICATION OF SETTINGS CURRENT DIFFERENTIAL (87L) SETTINGSL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 8-38Once all data is entered, by clicking the Analyze button, you can observe differential and restraint currents through thesimulated fault in the Results tab, shown as follows. The application is considered secure when the worst through the plotIrestr/Idiff > 1.25 with selected settings and all fault scenarios considered.Figure 8-2: Tool results for currentsFigure 8-3: Tool results for differential and restraint currentsYou are encouraged to test different fault locations and different fault levels and distributions per short circuit studies.Alternatively, the tool can help to estimate required CT parameters (ratio and knee point voltage), based on some pre-determined criteria.8.2 Current differential (87L) settings8.2.1 IntroductionSoftware is available from the GE Digital Energy website that is helpful in selecting settings for the specific application.Checking the performance of selected element settings with respect to known power system fault parameters makes itrelatively simple to choose the optimum settings for the application.
