ABB RELION Series Technical Manual page 498

Section 5
Protection related functions
492
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. In
case Flt Dist quality equals 1, the result is not affected by error sources. This results
in good quality for fault distance estimate. If factors affecting negatively to fault
distance estimation are detected, the Flt Dist quality is according to
case estimated fault distance, Flt distance value is given in HMI in parenthesis.
Table 514: 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 differs 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.
Even these can be omitted in the short circuit loops, if the setting Enable simple model
equals "TRUE".
If the impedance settings are in use, it is important that the settings closely match the
impedances of 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
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)
REC615 and RER615
1MRS758755 A
Table 514. In this
1)
loop
1)
loop
Technical Manual