ABB RELION 620 Series Technical Manual page 851

1MRS757644 F
620 series
Technical Manual
Fault loop "ABC Fault"
Fault loop "ABC Fault" is used exclusively for the three-phase short circuit fault.
Figure 437 shows the three-phase fault loop model. The following impedances are
measured and stored in the recorded data of SCEFRFLO.
Flt point resistance R
=
GUID-2503378E-4AC5-4E9F-9D77-2E7C71592C37 V3 EN
Flt loop resistance R
=
1
GUID-F9E2B211-9C30-4A81-ABD4-525CC10AB7A8 V2 EN
Flt loop reactance Flt phase reactance
=
GUID-049B892B-9031-4361-843B-7102E6A4DA17 V3 EN
GUID-359785B9-1D24-4751-B018-2225F04D7A2F V2 EN
Figure 437: Fault loop impedance for a three-phase fault loop ("ABC Fault")
The three-phase fault distance is calculated with a special measuring element using
positive-sequence quantities. This is advantageous especially in case of non-
transposed (asymmetric) lines, as the influence of line parameter asymmetry is
reduced. If the line is non-transposed, all the phase-to-phase loops have different fault
loop reactances. The use of positive-sequence quantities results in the average value
of phase-to-phase loop reactances, that is, the most representative estimate in case of
three-phase faults.
The fault distance calculation algorithm for the three-phase fault loop is defined by
using settings Load Com PP loops and Enable simple model. Options for the selection
are "Disabled" or "Enabled".
Load compensation can be enabled or disabled with setting Load Com PP loops. The
load compensation should be disabled only if the ratio between the fault current and
load current is large or when the value of the fault distance estimate for the short circuit
fault is required from each shot of an autoreclosing sequence.
The fault distance calculation is most accurate when the calculation is made with the
fault loop model. This model requires positive sequence impedances of the protected
feeder to be given as settings. If these settings are not available, valid impedance
values can be calculated also without the fault loop model with setting Enable simple
model = "TRUE". However, valid distance estimate, that is, the conversion of
measured impedance (''electrical fault distance'') into a physical fault distance
requires accurate positive sequence impedance settings.
Protection related functions
fault
R
+
fault
X
=
1
Section 5
(Equation 161)
(Equation 162)
(Equation 163)
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