In order to properly support, mount,
and install the electrical equipment, structures made of steel,
aluminum, wood, or concrete and associate foundations are required.
The typical open-type substation requires strain structures to
support the transmission-line conductors; support structures for
disconnecting switches, current transformers, potential transformers,
lightning arresters, and line traps, capacitor voltage transformers;
and structures and supports for the strain and rigid buses in the
station.
When the structures are made of steel
or aluminum, they require concrete foundations; however, when they
are made of wood or concrete, concrete foundations are not required.
Additional work is required to design concrete foundations for
supporting circuit breakers, reactors, transformers, capacitors, and
any other heavy electrical equipment.
Substation-equipment support structures
fabricated of steel or aluminum may consist of single wide flange or
tubular-type columns, rigid-frame structures composed of wide flanges
or tubular sections, or lattice structures composed of angle members.
Substation strain structures can be wood or concrete pole structures,
aluminum or steel lattice-type structures, or steel A-frame
structures.
Aluminum, weathering steel, and
concrete pole structures can be used in their natural unfinished
state. Normal carbon-steel structures should have galvanized or
painted finishes. Wood structures should have a thermal- or
pressure-process-applied preservative finish.
Aluminum structures are lightweight,
have an excellent strength-to-weight ratio, and require little
maintenance but have a greater initial cost than steel structures.
Weathering-steel structures can be field-welded without the special
surface preparation and touch-up work required on galvanized or
painted steel structures, and the self-forming protective corrosion
oxide eliminates maintenance.
In addition, the weathering-steel color
blends well in natural surroundings. Galvanized- or painted-steel
structures have a slightly lower initial cost than weathering-steel
structures; however, they require special treatment before and after
field welding and require more maintenance.
Lattice-type structures are light in
weight, have a small wind-load area, and are low in cost. Single
column support structures and rigid-frame structures require little
maintenance, are more aesthetically pleasing, and can be inspected
more quickly than lattice structures, but they have a greater initial
cost. In order to reduce erection costs, rigid-frame structures
should be designed with bolted field connections.
The design of supporting structures is
affected by the phase spacings and ground clearances required, by the
types of insulators, by the length and weight of buses and other
equipment, and by wind and ice loading. For data on wind and ice
loadings, see National Electric Safety Code©, IEEE Standard C2-2002,
or latest edition. For required clearances and phase spacings, see
Part I, Secs. 11 and 12.
Other structural and concrete work
required in the substation includes site selection and preparation,
roads, control houses, manholes, conduits, ducts, drainage
facilities, catch basins, oil containment, and fences.
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