ABB RELION REX640 Technical Manual page 1209

1MRS759142 F
Name
Al/Fe 93/39 Imatra
Al/Fe 108/23 Vaasa
Al/Fe 305/39 Duck
Table 1154: Positive-sequence impedance values for typical 33 kV conductors,
"Flat" tower configuration
Name
ACSR 50 sq.mm
ACSR 100 sq.mm
ACSR 500 sq.mm
Zero-sequence impedance values
Location of earth faults requires both positive-sequence and zero-sequence
impedances. For short circuit faults, zero-sequence impedances are not required.
The positive-sequence impedance per unit values for the lines are typically known
or can easily be obtained from data sheets. The zero-sequence values are generally
not as easy to obtain as they depend on the actual installation conditions and
configurations. Sufficient accuracy can, however, be obtained with rather simple
calculations using the following equations, which apply per phase for symmetrically
transposed three-phase aluminium overhead lines without ground wires.
R [ 50
0
R [ 60
0
≈ ⋅
X
0
R
1
W
ρ
earth
Table continues on the next page
REX640
Technical Manual
Hz ] ≈ R 1 0 14804 + . [ / Ω km
Hz ] ≈ R 1 0 17765 + . [ / Ω km

w
−
⋅ ⋅ +
4
2 10  3 ln 0 25 .
ω
n
r

en
conductor AC resistance [Ω/km]
ρ
earth
658
f
n
the equivalent depth [m] of the earth return path
earth resistivity [Ωm]
R1 [Ω/km]
0.335
0.287
0.103
R1 [Ω/km]
0.529
0.394
0.0548
]
]

Ω
 [ / km ]

Protection related functions
X1 [Ω/km]
0.344
0.344
0.314
X1 [Ω/km]
0.444
0.434
0.346
(Equation 307)
(Equation 308)
(Equation 309)
1209