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this case a fault that evolves from an external fault to an internal fault.
Differential Element
(DIFL)
Waveform Discriminating
Element (WDE)
Evolving fault detection
element (EVD)
Figure 2.4-1 Differential element with CT saturation countermeasure
The algorithm used in this element is given by Equations (2.4-1) to (2.4-3):
where,
ΔId: Change in the differential current Id
(ΔIp + ΔIn): Change in the restraining current in the positive and negative half cycles
Id: Differential current
Ip: Sum of positive input currents
In: Sum of negative input currents
m, m-1, m-2: Sampling timing
The SE will operate when the sum of the absolute values of the difference between the
instantaneous values of current data from one cycle is greater than a specified percentage of
minDIF-I.
where,
I
j
: Current at j
minDIF-I: A minimum value of between settings [DIFL-I1] and [DIFL-I2]
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