Overhead transmission line conductors are formed of layers of helically-layed strands with the direction of lay alternating layer to layer. Multistrand construction provides for the flexibility required for reeling, and permits cables to be manufactured in long lengths. The helical reversed lay form affords structural stability and is necessary to realize the flexibility offered by multistrand construction.

Conductors are available in a variety of designs relative to strand size, strands per layer, number of layers and choice of materials. The majority of designs employ strands of circular cross section, but others use trapezoidal strands. A few designs leave substantial gaps in inner layers to economize on metal where a certain overall diameter must be attained but high conductance is not justified. Other special designs exist.

This monograph deals with conventional round strand conductors with well packed layers. The geometry governing their design is addressed based on the concentric lay rule. The effect of lay ratio on the size of gaps between strands in a layer is determined and used to assess ASTM and IEC standards governing lay ratios. The effect of distortion of the strand cross section as it is bent to the helical shape is examined in an appendix.

Conductors are manufactured in stranding machines whose design affects the strains and stresses involved in forming the strands into helices. The residual stresses following stranding influence the handling characteristics of the finished cable. Stranding machines fall into two general classes relative to these stresses: rigid-head on one hand, and planetary and tubular stranders on the other.

The monograph analyzes the strains and stresses due to manufacture in each of these classes using the perfectly elastic - perfectly plastic model, leading to relationships covering the residual moments and torques in the strands. The departure of real conductor materials from the perfectly elastic - plastic model is determined and used to correct the residual moment and torque relationships.

The most significant practical impact of the residual stresses is upon the behavior of the cable when it is cut. This behavior is analyzed for cable manufactured in the two classes of strander. The use and limitations of preformers and postformers are discussed.

The monograph considers only materials now commonly used in overhead conductors: the 1350 and 6201 alloys of aluminum, extra high-strength galvanized steel and aluminum-clad steel. The analytical relationships developed in the text should be applicable to other metallic materials, however.

The monograph has the following chapters:

1. General purpose software
2. Introduction
3. Types of Stranders
4. Conductor Geometry
5. Strains During Stranding
6. Fabrication Stresses
7. Residual Stresses and Moments in the Strand
8. Springback of Strands Following Cutting
9. Preforming and Postforming

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