Instruction manual
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AQ F3x0 Feeder protection IED
24 (162
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3.2
P
ROTECTION FUNCTIONS
3.2.1
T
HREE
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PHASE INSTANTANEOUS OVERCURRENT
I>>>
(50)
The instantaneous overcurrent protection function operates according to instantaneous
characteristics, using the three sampled phase currents. The setting value is a parameter,
and it can be doubled with dedicated input binary signal. The basic calculation can be
based on peak value selection or on Fourier basic harmonic calculation, according to the
parameter setting.
Figure 8: Operating characteristics of the instantaneous overcurrent protection function,
where
tOP (seconds)
Theoretical operating time if G> GS (without additional time delay),
G
Measured peak value or Fourier base harmonic of the phase currents
GS
Pick-up setting value
The structure of the algorithm consists of following modules. Fourier calculation
module calculates the RMS values of the Fourier components of the residual
current. Peak selection module is an alternative for the Fourier calculation module
and the peak selection module selects the peak values of the phase currents
individually. Instantaneous decision module compares the peak- or Fourier basic
