Instruction manual
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AQ G3x7 Generator protection IED
36 (211
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3.2.3
R
ESIDUAL INSTANTANEOUS OVERCURRENT
I0>>>(50N)
The residual instantaneous overcurrent protection function operates according to
instantaneous characteristics, using the residual current (IN=3Io). 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 13: Operating characteristics of the residual instantaneous overcurrent protection
function.
tOP (seconds)
Theoretical operating time if G> GS (without additional time delay),
G
Measured peak value or Fourier base harmonic of the residual current
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 residual currents individually. Instantaneous decision module
compares the peak- or Fourier basic harmonic components of the phase currents into the
setting value. Decision logic module generates the trip signal of the function.
Below is presented the structure of the instantaneous residual overcurrent algorithm.