Toshiba GR200 Series Instruction Manual page 379

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 detected 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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Note: The implementation of such features is dependent upon the selection of hardware and
the configuration of functions. Several IED models do not support certain features. To
determine whether a particular feature has been implemented within an IED, identify the IED
ordering number; and check the order number at the "G&T position" referring to the
comparison table below. For more information, see
Table 2.28-1 Comparative table in respective ordering numbers
Inrush current detection function (ICD)
ICD
✓: Applicable
feature
NA: Not applicable
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Appendix: Ordering
.
Ordering No. at "G&T"
33
✓
GRL200 (Soft 033 & 037)
6F2S1914 (0.49)
37
✓