Braced Post technology has become the design of choice for transmission lines 138kV to 230kV over the last decade for its economic advantages, construction efficiency, visual aesthetics, and Narrower Right of Way requirements. Combining a line post insulator with a suspension insulator as a direct brace without the use of a davit arm can greatly decrease project cost while still improving mechanical performance of the line post alone by 1000%.
A braced post is intended for monopole construction which is not only more visually pleasing than the popular high voltage lattice structure but significantly more economical on both material cost and labor. Monopole construction can be fully assembled on the ground and raised in place by a single crane. Mounting insulators on the ground reduces the time spent in a bucket and amount of labor needed resulting in drastically safer methods for erecting structures that are inexpensive. BP technology is continuing to evolve, and today we are proud to promote the fact that braced posts are being considered and used for EHV transmission lines, specifically at 345kV voltage. MacLean Power Systems is determined to exceed traditional limits of braced posts. In the past a typical braced post simply combined a basic line post insulator with a standard suspension insulator. As the mechanical capabilities of common assemblies were being pushed it became clear that conventional hardware was limiting the potential strength. For example a common drop tongue end fitting used for both braced post and line post application would fracture far before the post began to buckle or brace showed signs of fatigue. A newly designed end fitting such as the ‘RAM’ Vertical Bundle Plate allows the assembly to meet its potential; join a high strength end fitting with a 3 inch line post and a 36k suspension unit and you have a braced post assembly that far exceeds any like it before.
When designing a braced post assembly you must consider the mechanical performance as well as electrical. As with any structural member the longer you make a beam, or in this case the line post insulator, the more cantilever strength you are sacrificing. Even in a braced post increasing the post section length can cause a considerable decrease in the working vertical performance of the assembly. Low frequency and critical impulse flash over aptitude are vital for proper conductor insulation and lengthening the post is the most effective way to achieve the required electrical values through increased strike distances. Finding the balance between electrical and mechanical capacity requires an in depth look into all components as well as the geometry of the assembly.
Braced posts are commonly use to support bundled conductors and the new ‘RAM’ Vertical Bundle Plate from MPS is an efficient alternative to common vertical conductor bundle hardware that is designed for high voltage application. Traditional vertical bundles hang in unison from the insulators at lengths varying from 20 to 30 inches. As the conductors swing from wind and other elements the shortest strike distance can become from the conductor directly to the tower or base. The ‘RAM’ Vertical Bundle Plate was designed to allow both conductors in a vertical bundle configuration to swing a full 90° independently with no contact to corona rings, weathersheds, and absolutely no reduction in dry arc distance.
Not having to consider swing conditions for determining electrical values can allow for shorter stronger braced posts. In addition to improved conductor freedom the entire bundle has been elevated from the common 20 to 30 inches below the insulators to directly in line with the assembly causing a more efficient phase to phase and phase to ground spacing. In certain cases the MPS ‘RAM’ Vertical Bundle Plate has allowed the end user to take up to 5 feet off the structures. Reducing structure height takes a large portion of material cost away because a shorter structure is also a thinner structure with smaller base diameters. The ‘RAM’ Vertical Bundle Plate is rated to 50k ultimate strength so it is ideal for high strength applications to increase span length. Combine shorter structures with longer spans means fewer structures with less material which means big savings for any project.