There are usually many factors that impact on the selection
of the structure type for use in an OHTL. Some of the more significant are
briefly identified below.
Erection Technique: It is obvious that different
structure types require different erection techniques. As an example, steel
lattice towers consist of hundreds of individual members that must be bolted
together, assembled, and erected onto the four previously installed
foundations.
A tapered steel pole, on the other hand, is likely to be
produced in a single piece and erected directly on its previously installed
foundation in one hoist.
The lattice tower requires a large amount of labor to
accomplish the considerable number of bolted joints, whereas the pole requires
the installation of a few nuts applied to the foundation anchor bolts plus a
few to install the crossarms.
The steel pole requires a large-capacity crane with a high
reach which would probably not be needed for the tower.
Therefore, labor needs to be balanced against the need for
large, special equipment and the site’s accessibility for such equipment.
Public Concerns: Probably the most difficult factors
to deal with arise as a result of the concerns of the general public living,
working, or coming in proximity to the line. It is common practice to hold
public hearings as part of the approval process for a new line.
Such public hearings offer a platform for neighbors to
express individual concerns that generally must be satisfactorily addressed
before the required permit will be issued. A few comments demonstrate this
problem.
The general public usually perceives transmission structures
as “eyesores” and distractions in the local landscape. To combat this, an
industry study was made in the late 1960s (Dreyfuss, 1968) sponsored by the
Edison Electric Institute and accomplished by Henry Dreyfuss, the
internationally recognized industrial designer.
While the guidelines did not overcome all the objections,
they did provide a means of satisfying certain very highly controversial
installations (Pohlman and Harris, 1971). Parents of small children and safety
engineers often raise the issue of lattice masts, towers, and guys,
constituting an “attractive challenge” to determined climbers, particularly
youngsters.
Inspection, Assessment, and Maintenance: Depending on
the owning utility, it is likely their in house practices will influence the
selection of the structure type for use in a specific line location.
Inspections and assessment are usually made by human inspectors who use
diagnostic technologies to augment their personal senses of sight and touch.
The nature and location of the symptoms of critical interest
are such that they can be most effectively examined from specific perspectives.
Inspectors must work from the most advantageous location when making
inspections.
Methods can include observations from ground or fly-by
patrol, climbing, bucket trucks, or helicopters. Likewise, there are certain
maintenance activities that are known or believed to be required for particular
structure types.
The equipment necessary to maintain the structure should be
taken into consideration during the structure type selection process to assure
there will be no unexpected conflict between maintenance needs and r-o-w
restrictions.
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