The Right of Way
Before we are going to discuss the classification of power lines, it is good to be acquainted with the concept of the Right-of-Way. Transmission lines are normally constructed on a tract of land known as right-of-way. In most cases, only one type of structure is used on a right-of-way. But there are also instances wherein different types of structures and different types of lines are being put.

A right-of-way may follow a straight path, or may change direction in order to avoid obstacles, which happen in many cases. This change in direction causes strain on structures, and the need to compensate from these strains causes the emergence of much type of Transmission Line Structures.

The general types of structures used on transmission lines are wooden poles, concrete poles, metal or steel poles, and lattice towers. These structures can be classified as tangent, angled, or dead-end structure, depending on how it is used in a line.

Dead-End Structures
Dead-end structures, or strain-termination structures, are used wherever a transmission line ends. It is specifically designed to withstand relative greater deal of stress and strain. Dead-end structures at the end of a transmission line are generally identified by insulator strings in the strain insulators.
Dead-end construction may also be found within transmission lines at any point where excess strain is placed on the structures or its components. Example of these is double dead-end, wherein it supports strain of each phase of a line in two directions.

Angle Structures
This structure type is used at points where a transmission line undergoes a significant change in direction. Angle structures are specially reinforced to withstand the strain placed on them by changes in direction.

Tangent Structures
This type is the most commonly used structure type on a transmission line. It is also called as straight-through/ along the line construction. It is generally located on relatively straight portions of a right-of-way.
Tangent structures must be capable of supporting each phase of a transmission line as it passes from one structure to the next. In most cases, the insulator strings on the tangent structures are mounted in the suspension position.

Factors Affecting Transmission Line Design
All of those transmission line structure types can be found on virtually any transmission line. Where and how particular structures are used depends on many factors. Some the more important factors are the following:

1. Ground Clearance
2. Load Requirements
3. Type of Terrain
4. Span Length Conductors
5. Weather Conditions

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