ABB RELION REX640 Technical Manual page 1116

Section 5
Protection related functions
1110
Positive-sequence impedance values
Fault location requires accurate setting values for line impedances. Positive-sequence
impedances are required both for the 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 actual installation
configuration. This minimizes the fault location errors caused by inaccurate settings.
The positive-sequence reactance per unit and per phase can be calculated with an
approximation equation which applies to symmetrically transposed three-phase
aluminium overhead lines without ground wires.
a

4
en
X 10 2 ln 0 5
−
ω
≈ ⋅ ⋅ +
1 n

r

GUID-4EF0F8A4-CBFD-4241-95E3-E56636AFD037 V1 EN
ω 2 ⋅ π ⋅ f
n
a
en
a
3
(
12
GUID-4A370F6B-6A24-4ABF-818A-7C7ABD13A771 V1 EN
Geometric average of phase distances [m]
a Distance [m] between phases x and y
xy
r Radius [m] for single conductor
GUID-3286D931-397B-4A95-A8CC-4B6F76D608DD V1 EN
Figure 602: Typical distribution line tower configurations
Example values of positive-sequence impedances for typical medium-voltage
overhead lines are given in the following tables.
Table 1045: Positive-sequence impedance values for typical 11 kV conductors, "Flat" tower
configuration
Name
ACSR 50 SQ.mm
ACSR 500 SQ.mm

. [ / km ]
Ω


, where f = fundamental frequency [Hz]
n n
a a
)
⋅ ⋅
23 31
R1 [Ω/km]
0.532
0.0725
1MRS759142 C
(Equation 272)
X1 [Ω/km]
0.373
0.270
REX640
Technical Manual