GUID-359785B9-1D24-4751-B018-2225F04D7A2F V2 EN
Figure 414: 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.
Estimation of fault resistance in different fault loops
The fault point resistance value provided by the impedance calculation is available in
recorded data Flt point resistance and it depends on the applied fault loop as shown in
Figure 415. In case of ground faults, the estimated fault point resistance includes the total
fault point resistance between the faulted phase and ground, for example, the arc and
grounding resistances. In case of phase-to-phase faults, the estimated fault point
resistance is half of the total fault point resistance between the phases. In case of a three-
phase fault, the estimated fault point resistance equals the total fault point resistance as per
phase value, for example, the arc resistance per phase.
Section 5 1MAC059074-MB A
Protection related functions
812 615 series ANSI
Technical Manual
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