ABB RELION REX640 Technical Manual page 1115

1MRS759142 C
REX640
Technical Manual
Result quality indicator
The quality of the estimated fault distance is judged and reported in recorded data as
the Flt Dist quality together with the fault distance estimate. The Flt Dist quality is a
bit vector indicating detected sources of inaccuracy in the fault distance estimate. If Flt
Dist quality equals 1, the result is not affected by error sources. This results in good
quality for the fault distance estimate. If factors affecting negatively the fault distance
estimation are detected, the Flt Dist quality is according to
estimated fault distance (Flt distance) value is given on the HMI in parentheses.
Table 1044: Fault distance quality indicator Flt Dist quality
Value
2
4
8
16
32
64
128
256
1) Xloop is the total loop reactance according to settings
For example, if fault point resistance exceeds 500 Ω and Flt to Lod Cur ratio is below
1.0, Flt Dist quality is "36". As another example, if no error sources are found, but
stability criterion is not met, the value of Flt Dist quality is "2".
Impedance settings
The fault distance calculation in SCEFRFLO is based on the fault loop impedance
modeling. The fault loop is parametrized with the impedance settings and these can be
set at maximum for three line sections (A, B and C). Each section is enabled by
entering a section length, which ranges from zero to settings Line Len section A, Line
Len section B or Line Len section C in the order section A-> section B-> section C.
The earth-fault loops require both positive-sequence and zero-sequence impedances,
for example, R1 line section A and X1 line section A, R0 line section A and X0 line
section A. For the short circuit loops, only positive-sequence impedances are needed,
but they can be omitted if the setting Enable simple model equals "Enabled".
If the impedance settings are in use, it is important that the settings closely match the
impedances of the used conductor types. The impedance settings are given in primary
ohms [ohm/pu] and the line section lengths in per unit [pu]. Thus, impedances can be
either given in ohm/km and section length in km, or ohm/mile and section length in
miles. The resulting Flt distance matches the units entered for the line section lengths.
Protection related functions
Table 1044. In this case, the
Corresponding inaccuracy description
Estimation stability criterion has not been reached
Fault point resistance exceeds 500 Ω
Fault point resistance exceeds 5 × X
Fault point resistance exceeds 20 × X
Flt to Lod Cur ratio is below 1.00
Fault distance estimate outside tolerances (<-0.1
pu or >1.1 pu)
Distance estimate calculation is not done due to
too low magnitudes of I or U
Distance estimate calculation cannot be
performed (for example avoiding internal division
by zero)
Section 5
1)
loop
1)
loop
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