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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