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2.38.5 Detection of current change (OCD)
(i) Current change detection relay
Suppose that the difference exists between the latest current vector (I
M
) and the last current
vector (I
N
). The OCD function will operate if the difference is larger than the setting. The I
N
is
measured for the last two-cycles; the difference is decided using Equation (2.38-1):
where a criteria for the decision is given by the pick-up threshold value (I
s
).
The pick-up threshold is defined using setting [OCD], which is from 0.05 A to 0.20 A at 1 A
rating†. At 5 A rating, 0.25 A to 1.00 A is applied.
Figure 2.38-4 Current change detection
(ii) OCD logic
Figure 2.38-5 shows the OCD logic and its output signals.
To Common of DISCAR, DEFCAR
Figure 2.38-5 Scheme logic for current change check
(2.84.4)
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