ABB COM600 series User's & Technical Manual page 28

28
COM600 series 5.1
Substation Analytics Technical Manual
Figure 4.3-23 An example of the ALARM output usage when alarm is given with location between
set limits
Impedance settings
The fault distance calculation in SCEFRFLO is based on the fault impedance loop
modeling. The fault loop is parameterized with the impedance settings, for example earth
fault loops ( fault loops 1, 2 and 3) require both positive and zero sequence impedances
as an initial data. For the short circuit fault loops (fault loops 12, 23, 31 and 123), only
positive sequence impedances are needed. Even these can be omitted if the Simple mode
PP loops = "Enabled". In this case, the conversion of electrical fault distance into a
physical distance cannot be done in the IED and the FLT_DISTANCE output is not
valid.
If the impedance settings are in use, it is important that the settings closely match the
impedances through which the fault current flows. The impedance settings, for example
R1 line section A, X1 line section A, R0 line section A, and X0 line section A, are given
in the units of primary ohm/pu and the line section lengths in per unit (pu). Pu can be
the unit that the user prefers and it allows the user to give the impedances in ohm/km
and length in km, for example, (pu = km), or impedance in ohm/mile and length in mile
(pu = mile). The resulting fault distance is also obtained in pu and it should match the
units entered for the line section lengths.
Table 4.3-1 Positive-sequence impedance values for typical 11 kv conductors,
"FLAT" tower configuration assumed
Name
ACSR 50 sq.mm
ACSR 500 sq.mm
alarm_output_usage_with_location_between_set_limits.png
R1 [Ω/km]
0.532
0.0725
1MRS758734
X1 [Ω/km]
0.373
0.270