Q121 : Why are Computed Step Voltages Asymmetrical in a System with Four-Sided Symmetry (i.e., a Transmission Line Tower)

Question
Why are Computed Step Voltages Asymmetrical in a System with
Four-Sided Symmetry.

Here are some possible reasons why computed step voltages are
asymmetrical in a system (a transmission line tower) with four-sided
symmetry:

1. If the "Gradient" type of step voltage is selected, then step voltages
are computed only in the direction of the potential profile and not in
any other. As a result, step voltages along two parallel sides of the
tower can be the same, but quite different from those on the other two
insides. The regular step voltage option should be selected to obtain
true step voltages.

2. If the spacings between points along each profile (as specified in the
PROFILE definition) are different from the spacings between the
profiles (as specified in the SURFACE definition), then step voltages
in the two different directions may be based on different point spacings
and therefore different. Remember that at each profile point, the
program searches within a default radius of 1 m (or a user-specified
radius, if any) for all other points: the voltage between the central point
and each other point is computed and the maximum is retained. If the
point furthest from the central point in one direction is much further than
the furthest point in the perpendicular direction (or maybe there are no
points within the search radius in the perpendicular direction!), then this
will introduce an asymmetry between the step voltages along different
sides of the tower.

3. Your profile points may not occur at the same distances from the tower
foundations/grounding on all four sides: i.e., there may be an
asymmetry in the positions of the profile points with respect to the four
sides of the towers.

Note that earth potentials, and therefore touch and step voltages, are
computed only at the profile points you define. Depending on the points
you choose, the results may vary somewhat.

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