Toshiba GR-200-5 Instruction Manual

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6F2T0207 (0.01)GRE200 (5,6)- 127 -Inrush current detection function (ICD)When a current transformer (CT) is first energized, an inrush current flows into the CTtransiently to establish the magnetic field. The magnitude of the inrush current can greaterthan the full load current so much; thus, the protection function can issue trip signals falsely.That is, the inrush current is required to detect and the protection functions shall not operateduring CT energizing. Inrush current detection (ICD) function is designed to detect a secondharmonic inrush current. This is because, the inrush current has all order of harmonics, butthe second harmonics is the greatest†. Signals generated in the ICD function are transferredto other protection functions to block their operations.†Note:The second harmonic current is present all inrush currents in three-phases. Theproportion of the second harmonic current varies with the degree of theenergizing, but the ratio of the second harmonic current to the fundamentalcurrent can be about 20% or greater during energizing.