Koi Koi Grace
by on March 16, 2019

2-) Assemblies and parts


The size and quantity needed of each material/component of a transmission structure is tabulated on the primary assembly and sub-assembly drawings. This list can be linked to PLS-POLETM, TOWERTM and PLS-CADDTM modules. PLS-CADDTM contains a powerful material management system that allows import of parts and assemblies from existing databases, generate material lists and costs for both construction as well as structural and line optimization. The Parts Editor helps store data related to structure parts (stock number, description, unit price, manufacturer and supplier). These parts can be used to build ‘assemblies’ and/or ‘sub-assemblies’.

Once the parts and assemblies library is developed in PLS-CADDTM, the associated assemblies and/or parts can be linked to its structure model. If optimization capabilities of PLS-CADDTM are utilized, the total cost of each structure is automatically calculated. Finally, once the structures are spotted, PLS-CADDTM can provide a listing of material and parts (and labor, if needed) in several formats.

Figures 3.29 and 3.30 show the concept behind developing assembly drawings for various sub-assemblies and parts. These are typical schemes and can be adjusted based on the requirements of the utility, project, type of structure and material.


3-) Framing Drawings

The term “Structure Framing’’ refers to the general location and arrangement of various components in a transmission structure to meet specific loading, geographical, right-of-way and construction preferences of the project under consideration. All transmission line structure designs are accompanied by drawings showing the framing of the assemblies – cross arms, X-braces, guying attachments, OHGW attachments, end fittings on the cross arms, fastener holes, washers, grounding assemblies etc. The framing requirements vary by structure and material configuration; but they must all satisfy the design criteria established for that particular project.

In the case of wood structures, the framing drawings indicate the heights of the wood poles, cross arms or davit arms and x-braces (for H-Frames) and OHGW/OPGW






attachment details etc. The depth of embedment (for tangent poles) is also sometimes shown. Framing guidelines for most RUS-standard structures can be found in relevant RUS Bulletins. Hole drilling can be performed on-site for most wood poles.

 In the case of steel structures, the framing drawings indicate the sizes of the tubular shafts, joints (splices or bolted flanges), insulator brackets, welded components, ladder clips, grounding nuts, davit arms, cross arms and x-braces (for H-Frames) and base plates/anchor bolt assemblies etc. The size of the concrete shaft foundation (or depth of embedment for tangent poles) is also often shown.

For concrete transmission structures, framing is more complex and timeconsuming. This is because the prestressed concrete poles contain stressed tendons inside and hole-drilling must be performed carefully. In most cases, the engineer will specify the insulator and ground wire attachment locations, line angles and structure orientation to the manufacturer; the drilling will be performed during fabrication. For lattice steel towers, structure framing is usually more complex and extensive. Assembly drawings show each angle member individually, their bolt patterns and location in the tower. Leg members are more carefully highlighted.

All data relevant to the structure, components and hardware will be listed on framing and assembly drawings. The high level of detail shown on these drawings depends upon various factors such as structure configuration, vendor/fabricator requirements, owner’s inventory stock numbers and manufacturer catalog numbers etc. Most of this information is reflected in the PLS parts and assembly databases so that a utility can track these items as part of their asset management process.

In the following sections, the component assembly drawings related to several structure families at various voltages will be discussed. The figures accompanying the discussion serve to illustrate the wide variation in the content of the drawings as a function of structural material and usage. These are only examples of typical framing drawings and a format used by RUS/USDA for structural systems.


 3-a) 69 kV family

Figures 3.31a to 3.31 g shows the assembly drawings for a family of wood structures for 69 kV applications. The first two refer to tangent poles but with different insulators (post and suspension mounted on braced cross arms) while the third sketch (Figure 3.31c) shows a popular configuration of an H-Frame system. The angle structure of the fourth drawing (Figure 3.31d) is similar to the tangent system of Figure 3.31b but uses swinging brackets to facilitate small line angles.

Figures 3.31e and 3.31f show single pole angle system and deadend. Note the use of a horizontal post insulator with jumpers for Type-1 deadend. The last sketch Figure 3.31g is a common form of a 3-pole angle deadend used at substations at the beginning (and end) of a line; one side is strung at full-tension while the other, going into the substation, is strung at reduced tensions. The number of anchors required for these deadends is a function of down guy tensions; for slack or low-tension spans, two down guys can share an anchor (see Figure 3.6a).


  3-b) 161 kV structures

Figures 3.32a to 3.32i shows the assembly drawings for a family of structures for 161 kV applications. The first four sketches show the drawings for insulators supported






3-c) 345 kV Structures

Figures 3.33a to 3.33g shows the assembly drawings for a full family of steel 345 kV structures with bundled conductors (two per phase). These drawings also illustrate the use of various special insulators handling multiple conductors. Note the use of three poles, large pole spacing, braced line posts (and yoke plates) for small angle locations and heavy-duty guying tees for medium angle structures. X-Braces for H-Frames are often custom-made since the large pole spacing requires longer brace lengths and therefore bulkier braces. Hughes Brothers (1953, 2000), for example, are one of the suppliers of specialty X-braces for large H-Frame systems; these heavy-duty braces are often made of steel tubular sections or laminated wood for higher buckling strength (see Figure 3.36c).

Figures 3.33d to 3.33g show several insulator assemblies that can be used for a typical bundled conductor application. The one visible difference between these assemblies and others is the presence of a corona ring which is generally used for all voltages above 115 kV. The last drawing (Figure 3.33g) also shows the use of a wire spacer yoke plate to maintain an 18 in. (45.7 cm) separation between wires for a bundled conductor application. This particular example shows a long (15 ft. or 4.57 m) strain string containing an extension link.


 3-d) Distrubition Structures

Figures 3.34a to 3.34c show three distribution poles with post, pin and suspension strings with swing brackets. At lower voltages, say less than 14 kV, a neutral conductor is also employed with pin insulators. The spans of these lines are generally less than 300 ft. (91.4 m) with smaller conductors. Most framing drawings for distributionlevel structures are available in RUS Bulletin 803 (1998) and Bulletin 804 (2005) supplemented Bulletins 150, 152 and 153 (all 2003).


3-e) Special Structures

Figures 3.35 shows the framing details of a 3-way air break switch built with a laminated wood pole. Note the large phase spacing of 22 ft. (6.7 m).


 3-f) Hardware

The eleven (11) drawings of Figures 3.36a to 3.36 k show various hardware items used in transmission line structures. These range from insulator strings, optical ground wire assemblies, X-braces for H-Frames, medium and heavy duty guying tees, swing brackets, davit arms, fiber optic deadend assemblies and grounding units. These drawings are only a representative sample of the type of hardware items used on transmission


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