Electrical Transmission & Substation Structures Conference 2025

Explore TRC’s Expertise at the Electrical Transmission & Substation Structures Conference

TRC Companies is proud to join the upcoming Electrical Transmission & Substation Structures Conference, the essential triennial event focused on electrical transmission line and substation structures and foundations.

Our experts will engage in sessions covering the latest advancements in analysis, design, construction, and maintenance, providing valuable insights for both seasoned engineers and emerging professionals. Attendees will discover innovative practices and practical solutions that enhance the safety, reliability, and efficiency of transmission and substation infrastructure.

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Abstract Description:

In the modern age of transmission line design, we face the challenge of expanding capacity and load growth while dealing with limited new real estate. This drives the need to optimize the existing right-of-way. Spacer cable systems, introduced in the 1950s for distribution voltages, have evolved into reliable solutions for various applications. Nearly 30 years ago, Marmon Utilities extended spacer cable use from 46kV to 69kV, providing compact and storm-hardened systems for higher voltages. In 2007, Marmon Utilities started developing a higher voltage spacer cable system, culminating in the first 115kV spacer cable system for transmission lines.

From 2019 to 2023, Marmon Utilities, TRC, and Liberty Utilities designed and installed the first commercial 115kV Hendrix spacer cable system. This line, energized in 2023, runs through a narrow 40ft-wide, 2-mile railroad corridor in Southern New Hampshire, now a public rail trail. It parallels a similar 115kV open-wire line built in 2021. These two 115kV radial lines address projected load growth and development.

The new lines replaced two 23kV circuits with vertically configured 115kV monopoles supporting 23kV spacer cable underbuilds. The east circuit uses OPGW, open-wire 115kV phase conductors, and 23kV Hendrix spacer cable underbuild; the west circuit uses OPGW, 23kV Hendrix underbuild, plus the new 115kV spacer cable technology. The two parallel lines provide a unique comparison of 115kV Hendrix spacer cable versus traditional open-wire design regarding geometry, framing, structure height, and project cost.

This paper explores the 115kV spacer cable system from the perspectives of the manufacturer, utility, and design engineer, including design considerations, constraints, and how it compares with traditional 115kV open-wire designs in design, space savings, materials, construction, and cost.

This unique geometry, design considerations and design constraints of the news 115kV Spacer cable system. The space saving abilities of the 115kV system to decrease the existing footprint within the right-of-way. How the 115kV spacer cable system compares to a similarly configured traditional open-wire design in overall design, space, material, construction and cost.