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 a
following approximation equation which applies to symmetrically transposed three-
phase aluminium overhead lines without ground wires.
X
a
r
km
n
en
1
4
10 2 0 5≈ ⋅ ⋅ +
−
ω
ln . [ / ]Ω
(Equation 306)
ω
n
2 × π × f
n
, where f
n
= fundamental frequency [Hz]
a
en
the geometric average of phase distances [m]
a
xy
distance [m] between phases x and y
r radius [m] for single conductor
Figure 689: Typical distribution line tower configurations
Example values of positive-sequence impedances for typical medium voltage
overhead-lines are given in the following tables.
Table 1152: Positive-sequence impedance values for typical 11 kV conductors,
“Flat” tower configuration
Name R1 [Ω/km] X1 [Ω/km]
ACSR 50 SQ.mm 0.532 0.373
ACSR 500 SQ.mm 0.0725 0.270
Table 1153: Positive-sequence impedance values for typical 10/20 kV conductors,
“Flat” tower configuration
Name
R1 [Ω/km] X1 [Ω/km]
Al/Fe 36/6 Sparrow 0.915 0.383
Al/Fe 54/9 Raven 0.578 0.368
Al/Fe 85/14 Pigeon 0.364 0.354
Table continues on the next page
Protection related functions 1MRS759142 F
1208 REX640
Technical Manual
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