Strong, lightweight Dyneema® helps engineer a breakthrough in overhead line crossing
Save time and money by eliminating scaffolding
Global engineering giant Amec Forster Wheeler was looking for a competitive edge in the world of overhead power line construction and maintenance. What could be done faster? What could be made safer? What could be simplified? The company’s Innovation Team identified scaffold towers as an area for improvement. And from that came a small but brilliant engineering breakthrough: the Skysok, a new overhead line crossing system made possible only with Dyneema®.
The challenge with overhead line crossings
The overhead power line dates back over 100 years. Yet while voltages, transmission tower design and materials have all advanced, when it comes to safely crossing highways, railroads, rivers, golf courses, parks and other high risk obstacles, the technology has remained much as it always was: erect scaffolding and hang nets.
It’s effective, but building huge scaffold towers and covering them with safety netting is expensive and time consuming. Recognizing the competitive advantage should they find a way to transform the age-old approach to power line maintenance, Amec Foster Wheeler’s Innovation Team wondered what would result if they started with today’s technologies and a clean sheet of paper. The team assessed best practices in the UK and around the world, and envisaged a radical approach. The goal: to completely eliminate the use of scaffolding and safety nets when works cross roads and highways, railroads, and public spaces.
From scaffolding to socks
The team had in mind a solution that could be extended out and around the high voltage cables themselves. A strong yet lightweight ‘sock’ that could be pulled along the powerline and so end the need for scaffolding and nets underneath. It would need to be capable of supporting the design load over spans of up to 450m, and be quicker and easier to deploy than scaffolding and nets. The number one priority, though, was safety.
Historically, the power line industry has employed steel wire based solutions and is very suspicious of synthetic rope based alternatives. But with high strength at low weight being central to the team’s idea, the use of synthetic fiber was critical. Amec Foster Wheeler therefore approached Harken Industrial, which it knew from its industrial rigger winches. Harken Industrial’s expertise in load handling, rope access, working at height, and safety – plus its partnership with rope manufacturer Teufelberger – would prove vital to the project. Harken further has experience in designing with ropes made with high strength, light weight Dyneema® fiber.
Stronger Than Steel ropes made with Dyneema®
Teufelberger STS (Stronger Than Steel) ropes are made with Dyneema® SK78 fiber and are around seven times lighter than steel wire ropes of the same diameter. This makes them extremely easy to handle. At the same time, they exceed the breaking strength of steel wire ropes of the same diameter. In short, the Harken/Teufelberger/Dyneema® combination offered the strength-to-weight ratio, flexibility, and ease of deployment benefits Amec Foster Wheeler was seeking.
In total, the project took 24 months. The main challenge Harken Industrial faced was to achieve the optimum balance between rope size, weight and performance in a package that could be deployed using as much existing equipment as possible. The company also needed to prove the safety and performance of a fiber rope to an industry in which steel wire rope is the standard. Harken Industrial and Teufelberger worked closely to fine-tune the Teufelberger STS design and ensure the specifications met all requirements. Harken supported AMEC Forster Wheeler with further trials to verify design calculations and modelling, to compile a detailed technical document for industry sign-off.
The Skysok overhead line crossing concept
The Skysok system that resulted makes it possible to replace multiple conductor configurations more efficiently, while minimizing the risk to infrastructure below. It works like this: the system is hauled into position and suspended from ropes that span from one tower to the next. The hauling lines are a 14mm industrial polyester rope. These hauling lines the pull tension lines made of high strength-to-weight Teufelberger STS from one tower to the next. The tension lines are held in place with winches, and tensioning them pulls the sock construction, made of polyester webbing over and around the powerline. The combination of safety sock plus tension lines made with Dyneema® then catches the powerline should it break or fall.
Skysok’s far better strength to weight ratio improves safety, logistics and mobility compared with using scaffolding and nets. The lower weight also reduces overall system weight and loadings back to the structure. Being lighter, the Skysok system is easier to handle physically, and being fiber-based it reduces wear on associated equipment compared with steel wire rope. And most importantly, rather than two to three days, with Skysok it only takes three to four hours to be in position and ready to go.
All as the Amec Foster Wheeler Innovation Team envisaged.