Koi Koi Grace
by on February 22, 2019
430 views

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.

Wood Pole With Steel Arms

For small projects, a PM-based process is not necessary; however, for large, time- and cost-constrained projects, where several entities and stakeholders interact, a formal PM-based approach is warranted. In such situations, project managers coordinate the design with engineers and serve to optimize costs, schedules and finally quality assurance and control. A brief description of each component of Detailed Engineering Design block is given below. Structure Locations: Before any design takes place, the engineer must finalize the alignment or route of the transmission line taking into consideration the various constraining criteria. These criteria include Right of Way (property boundary) and landowner issues, soil conditions, road and other clearances, cost and regulatory issues and construction access. Potential structure locations are identified and structures are “spotted’’ or placed at these points. Survey coordinates of the points when input to small projects, a PM-based process is not necessary; however, for large, time- and cost-constrained projects, where several entities and stakeholders interact, a formal PM-based approach is warranted. In such situations, project managers coordinate the design with engineers and serve to optimize costs, schedules and finally quality assurance and control.

A brief description of each component of Detailed Engineering Design block is given below.

Structure Locations: Before any design takes place, the engineer must finalize the alignment or route of the transmission line taking into consideration the various constraining criteria. These criteria include Right of Way (property boundary) and landowner issues, soil conditions, road and other clearances, cost and regulatory issues and construction access. Potential structure locations are identified and structures are “spotted’’ or placed at these points. Survey coordinates of the points when input to

Steel Pole with V-String Insulator

PLS-CADDTM will generate a 3-Dimensional Terrain to facilitate graphical assessment of the line.

Wire Sags and Tensions: This step involves determining the design tensions of the conductors and ground wires selected. Selection of optimum wire tensions is the most important activity of a transmission line design; the chosen tensions impact structure loads at line angles, sags under various weather situations, which in turn affect clearances, vibrations and forces in guy wires and anchors. Appropriate conductor tensions are also important at locations of line crossings where one line crosses another directly above or below. The sag of the wires and the mandated clearances will govern the eventual heights of the structures.

Structure Design: Transmission structural design basically involves ensuring safety and integrity of the system when subjected to various wire and climactic loads.

Steel Pole Tangent and 90 Degrees

Steel Pole - Deadend Tangent

This process must adhere to and satisfy various code and industry regulations defining the performance of the structure. Structural materials may differ but the underlying design concepts are the same.

Foundation Design: 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 as well as the variation of soil with depth and along the alignment. The choice of eventual foundation type will further depend on structure material and configuration and loads.

Design Drawings: The framing drawings show the full geometry of the structure, insulator and wire attachment points and heights. Individual hardware units and their sub-components are shown in the assembly drawings. Finally, the Plan and Profile (P & P) drawings constitute the view of the entire line – plan and elevation – and showing all significant features defining the terrain.

Prestressed Pole

 

Post in: Business