negatively to fault distance estimation are detected, the Flt Dist quality is according
to
. In this case estimated fault distance, Flt distance value is given in HMI
in parenthesis.
Table 811: Fault distance quality indicator Flt Dist quality
Value
Corresponding inaccuracy description
2
Estimation stability criterion has not been
reached
4
Fault point resistance exceeds 500 Ω
8
Fault point resistance exceeds 5 × X
loop
16
Fault point resistance exceeds 20 × X
loop
1
32
Flt to Lod Cur ratio is below 1.00
64
Fault distance estimate outside tolerances
(<-0.1 pu or >1.1 pu)
128
Distance estimate calculation is not done
due to too low magnitudes of I or U
256
Distance estimate calculation cannot be per-
formed (for example avoiding internal divi-
sion by zero)
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 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.
Positive-sequence impedance values
Fault location requires accurate setting values for line impedances. Positive-
sequence impedances are required both for location of short circuits and earth
1
Xloop is the total loop reactance according to settings
1MRS757644 H
Protection related functions
620 series
Technical Manual
845
