Category Archives: White Papers

Accuracy and Precision

The book Structural Engineering of Transmission Lines has a chapter The nature of wires in spans. This chart is from that chapter. The thin very loopy line is a plot of sag vs temperature as the line temperature is cycled through a rising and falling pattern. It shows, at least for this experiment, that the

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Tipload under Stringing conditions

The question was asked about how a tipload calculation could be done under stringing (initial) conditions. AS/NZS 7000:2016 describes final conditions throughout, although initial conditions are referred to in some of the appendices. Initial conditions is the state of the conductor when it is first installed. After installation, permanent (plastic) elongation occurs over the life

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Raising a crossarm

If you modify an existing span by raising or lowering the crossarm on one end of the span, what changes occur to the tensions? Power lines are modelled as catenary curves. “Although commercially available wires and cables are not truly flexible, they will, in very short spans, conform closer to a catenary than to any

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Level vs inclined spans

What difference does uneven attachment heights in a span make to tension? We can approach this issue by comparing tensions in two spans identical except for the vertical height difference. Equations are from AS/NZS7000:2016 For this worked example the spans have these common properties: Krypton conductor, weight 0.433 kg/m Conductor breaking load 37.4 kN 60m

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Modelling a stay

A distribution pole is in static equilibrium. The loads on the pole and any resistance to those loads are balancing each other out. Loads are due to conductor tension and wind load on the pole and conductors, and resistance is provided by the pole itself and stays. The resistance given by the stay is passive.

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Should you model streetlights?

When calculating the loading on a power pole (tipload) should you consider the effect of a streetlight? I selected a Sylvania Suburban as a typical light used on a distribution pole, mounted at 6.5m. Using the dimensions and weight from the manufacturer’s data sheet and adding a small allowance for the outreach, I create a

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Tension from Field Data

When assessing an existing span you are able to measure dimensions such as attachment heights, and often you want to derive the stringing tension of the span, or the sag under alternative temperature conditions. Data required for these calculations are: distances – span length, attachment heights (see figure 1) conductor type/properties air and conductor temperatures

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Wind Pressure reduced by cos²

In standards you will often see that wind pressure on a pole, conductor etc is reduced by cos² (or sin² depending on the orientation of angles) of the angle between wind direction and object direction but there is no explanation of why cos is squared. Here is the explanation. When moving air (wind) is stopped

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Loads on poles

Newton’s laws of motion In the 17th century Sir Isaac Newton developed three laws that explain why things move (or don’t move) in the way they do. They are commonly known as Newton’s laws of motion. These laws apply to all types of objects including planets and power poles (as long as their speed is

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