ABB Relion REC615, Техническое руководство

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The fault distance calculation is based on locally measured fundamental frequency
current and voltage phasors. The full operation of SCEFRFLO requires that all phase
currents and phase-to-earth voltages are measured.
The fault distance estimate is obtained when the function is externally or internally
triggered.
5.4.4 Operation principle
The fault distance calculation is done in two steps. First, the fault type is
determined with the inbuilt Phase Selection Logic (PSL). Second, based on the
selected impedance measuring element (fault loop) the fault distance from the
measuring point to the fault location is calculated.
As a fundamental operation criterion, the phase current and voltage magnitudes
must exceed the threshold values of 2% xIn and 3% xUn, respectively.
The function can be enabled or disabled with the
Operation setting. The
corresponding parameter values are “On" and "Off".
The operation of SCEFRFLO can be described with a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 248: Functional module diagram
5.4.4.1 Phase selection logic
Identification of the faulty phases is provided by the built-in Phase Selection
Logic based on combined impedance and current criterion. Phase selection logic
is virtually setting-free and has only one parameter,
Z Max phase load, for
discriminating a large symmetrical load from a three-phase fault. The setting
Z Max
phase load can be calculated using the equation.
Z Max phase load
U
S
xy
= ⋅
0 8
2
.
max
(Equation 45)
1MRS758755 C Protection related functions
REC615 & RER615
Technical Manual
497