Instruction manual
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AQ F3x0 Feeder protection IED
75 (162
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The applied numerical method is solving the differential equation of the faulty loop, based
on three consecutive samples.
The calculation for Zone1 is performed using two different methods in parallel:
•
To achieve a better filtering effect, Fourier basic harmonic components are
substituted for the components of the differential equations.
•
To avoid the influence of current transformer saturation, the differential equation is
solved directly with sampled currents and voltages. Under this method, sections of
the current wave where the form is not distorted by CT saturation are selected for
the calculation. The result of this calculation is matched to a quadrilateral
characteristic, which is 85% of the parameter setting value. In case of CVT swing
detection; this calculation method has no effect on the operation of the distance
protection function.
Figure 3-41: Impedance calculation principal scheme
The inputs are the sampled values and Fourier components of:
•
Three phase voltages,
•
Three phase currents,
•
(3Iop) zero sequence current of the parallel line,
•
Binary inputs,
•
Parameters.
