the fault distance estimation are detected, the Flt Dist quality is according to
Table
93
. In this case, the estimated fault distance (Flt distance) value is given on the HMI
in parentheses.
Table 1151: 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 performed (for example avoid-
ing internal division 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 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 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
faults. As data sheet impedance per unit values are generally valid only for
a certain tower configuration, the values should be adjusted according to the
1
Xloop is the total loop reactance according to settings
1MRS759142 F Protection related functions
REX640
Technical Manual
1207
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