Техническое чтение для энергетиков. Бухарова Г.П. - 58 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

60
in the course of the next 2 or 3 years.
Apart from the extra-high voltage aspect, however, there are a number of
features of design and construction which are worthy of mention. The first concern
the use of aerial photography for acquisition of the right-of-way** as well as spacing
and location of the line structures.
Initial reconnaissance of the route was made by helicopter, and aerial
photography was used to make final selection; then photographs of this route were
obtained to a scale of 200 feet to the inch. On these photographs were superimposed
all property lines, road boundaries, the boundaries of the proposed right-of-way and
legal descriptions of the property traversed. Final land survey for registration
purposes followed at a later date. The right-of-way acquired is 450 feet in width, to
provide for two additional similar circuits at some future date.
Concurrent with the selection of a suitable route was the design and fabrication
of the towers. The conductor selected was 795,000 circular-mil 26/7 steel-reinforced
aluminum cable, using a twin bundle per phase at 18-inch centers; phase spacing was
35 feet. The conductor was suspended from 21 unit insulator strings***, with
specially designed grading rings attached at the lower ends. The maximum design
tension in the conductor was one-half its ultimate strength. The maximum design
loading was 1/2 inch of radial ice, plus 4 pounds per square foot wind pressure at zero
degrees Fahrenheit. As the lightning incidence in this area is very low, ground wires
were installed for only 1/2 mile at the line terminals.
After considerable study as to the type of tower to be employed on this line, the
portal type was finally selected. Fig. 26 shows a tangent tower. This type of tower
offers a number of distinct advantages for this application. By the use of two masts,
instead of the quadruped construction normally used, the weight of redundant steel is
considerably reduced, particularly in the tower head. At extra-high voltages, this
reduction becomes increasingly important. Another advantage is that the two masts
offer very little obstruction to the use of agricultural equipment around the tower.
This was a factor, as 59 of the 64 miles of line pass
through highly cultivated farmland. The third advantage
lay in the ease of erection for this type of tower.
The specification called for a standard mast to be
designed to meet the requirements for tangent, angle,
and dead-end towers. On angle towers, the transverse
load was to be taken by internal guys, and similarly, on
deadend towers the conductor tension was to be taken
by guys. Thus, the mast designed for the tangent tower
could be used for all towers, and only separate
crossarms need be detailed. This effected a considerable
saving in detailing cost and simplified erection.
The maximum line span was 1,222 feet and the
minimum 514 feet. The average span was 995 feet.
Every suspension tower was to be capable of
withstanding a longitudinal load due to both conductors
Fig. 26.

Страницы