Shemar Braced Line Post Insulators
/115kV to 230kV
Line Compaction
The need to increase power transmission capacity in a sustainable and recourse conscious manner has amplified interest in line compaction. Line compaction is the process of reducing height and width of transmission line structures so that they are lighter and can be fitted into narrow right-of-ways. Today, in addition to being deployed in narrow corridors, compact transmission lines are being used to deliver a variety of other benefits, such as, higher surge impedance loading of the circuit, lower visual impact and easier integration with landscape, reduced electromagnetic field (EMF) levels, improved reliability, efficient construction and overall lower cost of ownership.
Composite Braced Line Post Assemblies
The simplest insulator system for compact transmission line construction is a composite horizontal line post. However, line post insulators are limited in their vertical loading capabilities and thus cannot support longer spans or heavier conductor systems. Composite braced line posts are designed for applications similar to a line post but with an added suspension 'brace' insulator to significantly increase the vertical load capacity of the assembly.
Application Combined Working Load Curves of 2.5'' Line Post vs 2.5'' Braced Line Post
Braced line post assemblies feature excellent combination of cantilever characteristics of a horizontal line post insulator with the tensile strength of a suspension insulator resulting in a robust insulator system. The suspension insulator, also known as a brace, is linked to both the line post and the transmission support through connection hardware. Under load, the brace is subjected to tension and acts as the primary support for the assembly. Meanwhile, the line post offers stability against transverse and longitudinal forces acting on the assembly. The utilization of braced line posts as a form of insulated cross-arm assembly reduces the overall size of the transmission structures making construction more efficient and the design is able to restrain the conductor position thus reducing the required right-of-way to construct lines. These assemblies are an excellent choice for producing aesthetic transmission structures with minimized carbon footprint and community impact. Moreover, SHEMAR's brace line post assemblies also bring the inherent benefits with come with use of our best-in-class composite silicone rubber insulators including superior contamination and vandalism resistance and light weight. Please refer to our catalogues of composite suspension and post insulators for more information about our product design and features.
SHEMAR Braced Line Post Catalogue and Design Options
SHEMAR standard braced line post insulator assemblies are listed in this catalogue. In addition to these typical designs, custom braced line post or high strength CICA (composite insulated cross-arm) assemblies can be designed to meet customer's specific requirements.
Catalogue Number Definition - SHEMAR catalogue number for composite braced line post assemblies consist of ten parts as defined in the table below.
Design Options
The standard design of SHEMAR braced line post assembly features a drop tongue line end fitting, and a bendable base pole mount. The bendable base can be provided in both gain and flat designs, and can even be replaced with a pivoting universal joint to accommodate high longitudinal load applications.
SHEMAR provides customers with the flexibility to choose from various end fitting combinations for the suspension insulator that forms the brace. Eye-Eye end fitting combination is offered by SHEMAR as a standard design option, since this end fitting type when combined with anchor shackles results in a greater degree of articulation. In addition, YClevis-Ball combination can also be provided which can deliver the best compromise between articulation and live-line maintenance requirements. SHEMAR also provides adjustable turnbuckles in the brace connection hardware allowing flexibility in the assembly connection height.
Different Suspension Brace Hardware and Designs
Eye-Eye Suspension End Fittings with Anchor Shackles
Eye-Eye Suspension End Fittings with Anchor Shackles and Turnbuckle
YClevis-Ball Suspension End Fittings with Anchor Shackle, Socket-Clevis and Turnbuckle
Corona Ring Recommendations
At SHEMAR, our composite insulators are carefully engineered to eliminate RIV and corona (under both dry and wet conditions). Rather than taking a one-size-fits-all approach, we design our corona rings in accordance with the actual requirements and use of the individual user. To achieve this, our application engineers utilize state-of-the-art 3D modeling and FEA simulations to determine the optimal size and placement of corona rings based on the specific structure design and overall assembly configuration. It is ensured that the maximum electric field criteria of ≤ 4.2 kVrms/cm on silicone rubber housing recommended by EPRI is maintained on all of our designs and thus the phenomenon of water droplet induced corona (WDIC) and corresponding risk of material erosion is avoided. All of our corona rings are designed with an open (c-section) style or as two-piece system, making them easy to install and replace.
E-field FEA Simulation of Brace Post Assembly and Optimization of Corona Rings
The following general corona ring recommendations are developed to adhere to EPRI's E-field magnitude limits. However, it is important to acknowledge that the magnitudes of E-fields may differ based on the design and layout of the structure and must be confirmed by examining the E-field model of the entire assembly.
Recommended Corona Rings for Braced Post Assemblies
Braced Line Post Assembly - Class 250
2.5 inch Post and 25 kip Brace Insulator - Dimensions and Ratings
Components
2.5” line post insulator with bendable gain base
25 kip suspension insulator with Eye-Eye end fittings
25 kip turnbuckle (6” or 12” adjustable length)
25 kip anchor shackles (2 Nos.)
Corona rings (as appropriate)
Definition of Assembly Dimensions
PL - Assembly Section Length
SL - Suspension Insulator Section Length
BL - Assembly Brace Section Length
H - Assembly Height
A – Assembly Internal Angle
Braced Line Post Assembly - Class 300
3 inch Post and 50 kip Brace Insulator - Dimensions and Ratings
Components
3.0” line post insulator with bendable gain base
50 kip suspension insulator with Eye-Eyeend fittings
50 kip turnbuckle (6” or 12” adjustable length)
50 kip anchor shackles (2 Nos.)
Corona rings (as appropriate)
Definition of Assembly Dimensions
PL - Assembly Section Length
SL - Suspension Insulator Section Length
BL - Assembly Brace Section Length
H - Assembly Height
A – Assembly Internal Angle
Application Combined Load Curves
Braced line post assemblies are designed and rated mechanically as a 'system' where the strength and stability of the insulator FRP cores, metallic hardware, fittings and bolted connections are considered and sized to provide required load withstand performance. During operation, these assemblies are subjected to combined loads which include vertical load (due to conductor), transverse load caused by wind and line angle as well as longitudinal load resulting from unbalances in span lengths, elevations, ice accretions or broken conductors. SHEMAR can provide combined load curves upon user's request. These are application or working load curves that can be applied to the braced line post assembly without exceeding the damage limit of the insulators. The combined load curves are generated analytically and validated with FEA simulations and full-scale testing.
FEA Simulation of Brace Post Assembly Stress and Deformation
Application load curves should be consulted to assure all load combinations are within the capabilities of the specific application. During transmission line design, the maximum anticipated loads should fit within the envelope of the working load curves.
An Example of Combined Load Application Curves of 230kV Braced Post Assembly
SHEMAR: Industry Leader in Line Compaction Solutions
In some cases, the strength capabilities of off-the-shelf braced line posts are unable to satisfy customer's specific requirements. In such situations SHEMAR specialist engineers can work closely with the customer's team to develop an engineered high strength composite insulated cross-arm (CICA) solution. The high strength CICA differs from two-dimensional structures like braced line posts or horizontal Vees. It is composed of at least three insulators positioned in a triangulated configuration, enabling the assembly to withstand significantly higher vertical, transverse, and longitudinal loads. Common configurations of CICA are below and these include: (1) Tetrahedron Cross-arm featuring a single line post and three suspension brace insulators, (2) Tripod Cross-arm with two line post insulators braced by a single suspension insulator and (3) Double Vee Cross-arm composed of two line post insulators braced by two suspension insulators. The optimal configuration amongst these options is chosen by balancing the loading withstand requirements along with the cross-arm weight and cost. These CICA assemblies can be used on both lattice towers and tubular supports.
Tetrahedron
Tripod
Double Vee
SHEMAR is a world leader in compact-line composite insulation system design and manufacturing. SHEMAR's CICA solution overcomes the limitations and technological gaps of traditional braced line posts or pivoting horizontal Vee. The application of CICA delivers the following additional benefits to electric utilities:
Enhance load capacity of transmission lines including longitudinal load security
Cut construction costs by allowing longer span lengths and lesser structures
Enable compaction up to 765 kV
Increase power transmission capacities by allowing heavier conductor bundles
Enable voltage uprating and improve ground clearance in retrofit applications
