Instruction manual
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AQ G3x7 Generator protection IED
64 (211
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Figure 3-35: Directional decision characteristics.
The voltage must be above 5% of the rated voltage and the current must also be measurable.
If the voltages are below 5% of the rated voltage then the algorithm substitutes the small values
with the voltage values stored in the memory. The input signals are the RMS values of the
fundamental Fourier components of the three-phase currents and three phase voltages and
the three line-to-line voltages.
The internal output status signal for enabling the directional decision is true if both the three-
phase voltages and the three-phase currents are above the setting limits. The RMS voltage
and current values of the fundamental Fourier components of the selected loop are forwarded
to angle calculation for further processing.
If the phase angle between the three-phase voltage and three-phase current is within the set
range (defined by the preset parameter) or non-directional operation is selected by the preset
parameter the function will operate according to the selected “Forward”, “Backward” or non
directional setting.
Operating time of the function can be definite time or IDMT based on user selection. Operating
characteristics of the IDMT function are presented in the chapter 3.1.2 Three-phase time
overcurrent protection I>, I>> (50/51).
