ABB RELION Series, Technical Manual

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Figure 249: 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
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(Equation 45)
U
xy
Nominal phase-to-phase voltage
S
max
Maximum three-phase load
For example, if U
xy
= 20 kV and S
max
= 1 MVA, then Z Max phase load = 320.0 Ω.
The identification of the faulty phases is compulsory for the correct operation of
SCEFRFLO. This is because only one of the impedance-measuring elements (fault
loops) provides the correct result for a specific fault type. A three-phase fault is an
exception and theoretically it can be calculated with any of the fault loops. The fault
loop used in the fault distance calculation is indicated in the recorded data Flt loop as
specified in
Table 512 .
1MRS758755 A
Section 5
Protection related functions
REC615 and RER615 483
Technical Manual