Toshiba GR-200 Series Instruction Manual page 147

Inrush current detection function (ICD)
When a current transformer (CT) is first energized, an inrush current flows into the CT
transiently to establish the magnetic field. The magnitude of the inrush current can greater
than 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 operate
during CT energizing. Inrush current detection (ICD) function is designed to detect a second
harmonic inrush current. This is because, the inrush current has all order of harmonics, but
the second harmonics is the greatest†. Signals generated in the ICD function are transferred
to other protection functions to block their operations.
†Note: The second harmonic current is present all inrush currents in three-phases. The
proportion of the second harmonic current varies with the degree of the
energizing, but the ratio of the second harmonic current to the fundamental
current can be about 20% or greater during energizing.
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6F2T0200 (0.15)
GRE200 (1,2)