ABB RELION REX640 Technical Manual page 895

1MRS759142 C
REX640
Technical Manual
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Figure 481: The fault loop impedance model for phase-to-phase impedance
measuring elements
R Positive-sequence resistance from measuring point to fault location
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X Positive-sequence reactance from measuring point to fault location
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R Physical fault resistance between phases, for example, arc resistance
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The phase-to-phase impedance measuring elements measure only
half of the physical fault resistance between phases. This must be
taken into account when the resistive reach of the phase-to-phase
elements is set (that is, setting the value of 5 Ω corresponds to 5 + 5=10
Ω of physical arc resistance between phases).
The resistive reach setting is common for phase-to-phase and three-phase impedance
measuring elements.
The operation time delay is defined with the setting PP operate delay Znx (x = 1... 5).
The timer can be disabled with the setting PP Op delay Mod Znx = "False". This blocks
the OPERATE_Zx (x = 1... 5) output of the phase-to-phase measuring elements.
Three-phase impedance measuring element
DSTPDIS has a dedicated measuring element for a three-phase short circuit fault for
each zone. The three-phase measuring element uses the positive-sequence quantities
for a fault loop impedance estimation which increases the accuracy by reducing the
influence of line parameter asymmetry. This is advantageous especially in case of
non-transposed, asymmetrical lines. The three-phase impedance measuring element
is enabled together with the phase-to-phase impedance elements by the setting Op
Mod PP loops Znx (x = 1... 5) = "True".
The reach of the three-phase measuring element is based on the loop impedance
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Section 4
Protection functions
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