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 help...
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by on March 15, 2019
The actual design of a transmission structure not only involves checking the strength and suitability of various components, but also ensuring that all materials and components meet the requirements of the governing standards or codes. Important items such as grounding are also a part of final structure design configuration and are briefly reviewed.   1-) Strength Checks The following sections cover code-mandated design checks for wood poles, steel poles, lattice towers, concrete and co...
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by on March 12, 2019
This section deals with the theoretical basis for analysis procedures for various transmission structure forms and types. Computer programs such as PLS-POLETM and TOWERTM are generally employed by most utilities; some utilities also have their own in-house programs for structural analysis, in addition to general purpose finite element programs. However, it is important to understand the underlying basis and limitations of these programs. The basics of analysis of various systems will be illustra...
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by on March 11, 2019
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by on March 11, 2019
Determination of analysis loads on transmission structures involves the following: 1. Wire Loads – vertical, transverse and longitudinal loads on wires due to ice, wind, temperature 2. Structure Loads – vertical, transverse and longitudinal loads on structure due to wires, attachments and hardware Secondary loads include those due to P-Delta (2nd Order) effects which will be discussed below.   1-) Load Cases and Parameters   The weather conditions considered for structural d...
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by on March 9, 2019
All transmission lines consist of structures mostly of the same material but of different sizes, insulator, line angle and loading configurations. These can be grouped into a “family’’ of structures specific for the project. Once the basic structure type (usually tangent) has been established, the “family’’ can be set up by adding systems of other configurations, specifically angle and deadend structures. In other words, the structure family basically contains tangent, angle (small, medium, larg...
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by on March 8, 2019
This section covers the structural and material properties of various elements that comprise a typical transmission structure. The three basic construction materials for transmission structures are wood, steel and concrete, although fiber glass (composite) poles and cross arms are being increasingly used for both transmission and distribution lines. Composite cross arms are also becoming popular for distribution under-build circuits on transmission poles given the ease of installation and struct...
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by on March 6, 2019
Transmission structures, whether wood, steel, lattice, concrete or composite, are one of the most visible elements of an electrical power transmission system. Regardless of material, they serve a single purpose: supporting the insulators, wires and equipment. The choice of a particular type of structure – material and configuration – for a transmission line, however, depends on several factors such as electrical, spatial, structural and economy. Electrical factors include voltage, number of c...
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by on March 5, 2019
The design of transmission line structures involves both analysis of the structural system – wires, supports and foundations – as well as design checks ensuring compliance with established norms and guidelines. Worldwide, most countries have institutions and standards devoted to design, construction and safe operation of utility structures. These standards or codes cover a variety of parameters such as loading, conductors, materials (steel, wood and concrete), hardware, clearances, performance a...
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by on March 4, 2019
Constructability refers to the “readiness to be built’’ and to the process of reviewing and ensuring that a particular transmission line project can be actually built as designed, given the numerous technical and non-technical parameters that control the construction phase. This “review’’ looks at the construction constraints, environmental barriers, political issues, risks and acceptance to local community.   a-) Construction considerations The primary construction-related issue is ava...
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by on March 2, 2019
Each structure must be securely embedded or anchored into the ground and facilitate safe transfer of structure loads to the ground strata below. To determine foundation requirements, the engineer must first evaluate the nature and condition of the soil in the vicinity of the structure. The choice of eventual foundation type will further depend on geotechnical characteristics of strata underneath, structure material, configuration, loads, constructability and economy. A majority of tangent poles ...
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by on March 1, 2019
The utility industry now uses tubular steel poles as well as steel lattice towers, spun prestressed concrete poles, wood poles and composite poles. Simple suspension (tangent) and small-angle single pole structures can be quickly analyzed using spreadsheets. The advent of powerful digital computers and software such as PLS-POLETM, TOWERTM and PLS-CADDTM, now enables accurate modeling and analysis of not only individual structures of a transmission line but also the entire transmission line in a ...
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by on February 27, 2019
1-) Structure spotting Prior to any design, the engineer must establish the alignment of the transmission line taking into consideration the various criteria. These criteria include property boundary issues, soil conditions, road and other clearances, regulatory issues, environmental concerns, costs, impact on public property, aesthetics and construction access. Potential structure locations are identified along the chosen alignment using structure spotting process. Structure spotting is the ...
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by on February 26, 2019
3-) Shielding When lightning strikes a transmission line, it may hit either the overhead ground wire or a phase conductor. If a conductor is hit, there will certainly be a flashover of the insulation. To prevent and minimize such an occurrence, the overhead ground wire is used to intercept the lightning strike, “shielding’’ the conductors. To optimize this shielding, the shielding angle (see Figure 2.4) must be 30◦ or less. If a location is known to have an unusually high exposure to lightnin...
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by on February 25, 2019
2-) Electrical Design Overhead transmission lines are designed to satisfy a wide range of local and regulatory requirements. While the demands of these requirements vary from location to location and are often line-specific, the underlying principle is one of legality, safety and reliability.   2.a) Regulatory Codes These relate to the local and national standards pertaining to both electrical operations as well as other land use considerations. For example, in areas close to runways...
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by on February 22, 2019
The process of designing an overhead transmission line involves various phases or sub-processes. From a Project Management (PM) perspective, there are five (5) main sequential phases as shown in Figure 1.9. This blog is concerned with Detailed Engineering Design, which includes structures and foundations. The basic contents of each of the sub-processes are shown in Figures 1.10, 1.11 and 1.12. The other sub-processes will be discussed in the companion volume. For small projects, a PM-base...
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by on February 22, 2019
Historically, the term “transmission structures’’ usually implied iron or steel latticed towers. The early “pylons’’ dating back to 1829 were iron structures; the basic shape of later pylons was mostly inspired by the famous Eiffel Tower. Figure 1.1 shows some of the early shapes and forms of transmission structures. Single wood poles directly-embedded into the ground formed the bulk of the transmission structures family for a greater part of the 20th century. France in the late 1900s and...
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by on February 21, 2019
   Count Alessandro Volta (1745−1827), the Italian physicist and inventor of the battery, was the first person to suggest the idea of a transmission line by writing in 1777 “… the igniting spark could be transported from Como to Milan with barbed wire supported by wooden poles planted here and there …’’ The structures in use those days for telegraph poles were wooden poles with zinc iron barbed wire supported by porcelain insulators fixed to the pole with screws and bolt hooks (TERNA, 2013). The...
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