Instruction manual
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AQ G3x7 Generator protection IED
106 (211
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For the equivalent impedance elements of the fault loop on figure above the following
differential equation can be written:
If current and voltage values sampled at two separate sampling points in time are substituted
in this equation, two equations are derived with the two unknown values R and L, so they can
be calculated.
This basic principle is realized in the algorithm by substituting the sampled values of the
line-to-line voltages for u and the difference of two phase currents in case of two- or three-
phase faults without ground for i. For example, in case of an L2L3 fault:
In case of a phase-to-earth fault, the sampled phase voltage and the phase current
modified by the zero sequence current have to be substituted: