Statistical Evaluation of PLS-CADD Batch Thermal Calculator Results

This is a presentation I gave on using statistics to identify outliers and potential input errors in PLS-CADD batch thermal calculations.

Transmission Line I-String Insulator Swing Calculations

I-string insulators are insulators that attach to a structure at one end, via a pinned connection, and support a conductor at the other end, via a suspension clamp or other hardware. They typically consist of a series of porcelain or glass insulator bells (Figure 2) or a polymer rod (Figure 1). Their attachment to the structure via a pinned connection allows the insulator to freely swing with imbalances in wire tension loads. This flexibility helps reduce the lateral loads on transmission line structures due to temporary tension imbalances. In the event of a broken wire on a tangent or angle structure, the insulator is also capable of swinging until a new equilibrium is obtained, dissipating energy and reducing the tension that the structure must support under a broken wire scenario.

While the ability of an I-string insulator to swing is beneficial due to its flexibility, excessive flexibility can result in the insulator swinging too far toward the structure or other nearby objects, developing electrical clearance issues. To verify that the swing provides adequate clearance to the structure, designers typically calculate the allowable minimum and maximum swing angles that an insulator of a specified length must reside between in order to maintain clearances. The expected insulator swings due to loads (wire tensions, wind loads, etc.) are then calculated and compared versus these limiting angles to ensure that the design is in conformance.

This post will present derivations of the equations necessary to perform I-string insulator swing checks, as well as to determine the deflected wire attachment location in space for use in sag-tension or other calculations.

Transmission Line Jumper Clearance and Minimum Line Angle Calculations

In order to maintain electrical clearances within transmission line dead-end structures, jumper supports, such as horizontal posts or I-string insulators supported on davit arms, are occasionally required in order to restrain the jumper away from the structure. Most often, they are required for in-line dead-ends (structures with no line angle) or dead-ends with small line angles; whereas, structures with large line angles, such as that shown in Figure 1, do not require jumper supports since the length of the insulators alone provide an adequate offset distance from the structure.

This post will present equations to assist in evaluating the clearance between a jumper and pole with and without jumper supports. In addition, an equation to calculate the minimum line angle required in order to maintain electrical clearances to the pole for a structure without a jumper support will be presented, as this value can be beneficial in making general design decisions or specifying limits for structures within design standards.