ABB COM600 series User's & Technical Manual page 30

30
COM600 series 5.1
Substation Analytics Technical Manual
a distance [m] between phases x and y
xy
r radius [m] for single conductor
Figure 4.3-25 Typical distribution line tower configurations
Zero-sequence impedance values
The zero-sequence impedances per unit are needed only with earth-fault localization.
With the localization of two-phase or three-phase short circuit fault, positive-sequence
impedances per unit are sufficient.
The positive-sequence impedance per unit values for the lines are known or can easily
be obtained from datasheets. The zero-sequence values are not so easy to obtain as they
depend on the actual installation conditions and configurations.
Sufficient accuracy can be obtained with rather simple calculations with certain equations
(applies per phase for symmetrically transposed three-phase aluminum overhead lines
without ground wires).
Figure 4.3-26 (Equation 16)
Figure 4.3-27 (Equation 17)
1MRS758734
typical_distribution_line_tower_configurations.png
equation_16.png
equation_17.png