Bridging electric rivers
During this year’s fifth Annual Construction Risk Assessment seminar, various industry leaders spoke about their operations, challenges and practices. One innovative idea from Eskom may prove to be a life-saver.
Held on August 21 and 22 at the Radison Blue hotel in Sandton, the fifth Annual Construction Risk Assessment conference provided a platform for leading construction risk and insurance professionals to gather, network and learn from each other. Various speakers offered a great deal of insight in regard to their industries.
Among these was Bertie Jacobs, chief technologist at Eskom, who spoke about how the organisation has been working hard to lessen the risks involved in the construction of overhead power lines. Jacobs has more than 15 years’ experience and specialises in overhead line design.
When new lines are added to our power grid, it is sometimes necessary for them to cross over existing power lines, roads, or railways.
Considering that it is impossible to simply “switch off” a power line, if the need arises to construct power lines over existing ones, overhead line construction must be undertaken with thousands of volts of electricity always present. The voltage of power lines currently ranges from 132 kV to 765 kV.
Jacobs also made it clear that each overhead construction brings a different set of challenges. The steps involved in constructing overhead power lines are laborious and must often be adapted to constantly varying situations.
First, digging and casting of foundations for the lattice structures adjacent to the existing power lines is undertaken. Each lattice structure comes with its own pros and cons. Newer cable-suspended and cross-rope type lattices are cheaper to manufacture and quicker to install than their four-legged older brothers. However, they take up a much larger area as they have many suspension cables which cover a large diameter. Furthermore, they are impractical for certain terrains.
Once the dressing, stringing and regulating of the conductors and earth wires is compete, the attachment and further installation of line accessories such as vibration dampers, bird flight diverters and aircraft warning spheres commences. In theory, this is a simple process. But, uneven terrain, the different types of lattices, roads and railroads all affect the construction process in some way, often to the frustration of engineers.
Another problem is the sheer logistics of power line construction. Given the immense distances that are covered while setting up power lines, supervision is difficult, making the risk involved even greater.
Traditionally, overhead line construction was done by setting up scaffolding on either side of the existing line, and then suspending the power lines across these two installations. However, due to difficult terrain and the fact that scaffolding puts workers dangerously close to live power lines, this has been abandoned.
Another option employed by Eskom in recent years was using truck-mounted cranes with running blocks attached to them in which the power line installers could be lifted above the live lines. This had its own unique set of dangers, however and, due to the limited number of cranes available for this type of operation, it was discarded.
As such, Jacobs and his team had to devise a new process to eliminate the risks involved with scaffolding and crane installation procedures.
For use in confined spaces and long-distance spans, Eskom’s engineers devised a “bull horn” system which works in conjunction with safety nets spanned over the live power lines. Mounted on a crane, these bull horns do the job of hoisting the overhead power lines and safety nets over the existing live lines, instead of utilising a running block with workers inside, thus considerably reducing the risk of electrocution.
The new overhead wires are then spanned and attached to their lattices in a much safer way. Despite this, there still exists the logistical problem of the scarcity of cranes capable of supporting the bull horn structure, and the vast distances covered when constructing power lines.
A new hybridised system is being developed by Jacobs and his team. A new running block structure has been designed to utilise the safety nets that are spanned over live power lines. This system allows for an operator to be present in a scaffold structure attached to the running block, making them considerably safer than their predecessors, and making it possible for workers to be in relatively close proximity to live power lines with a minimal amount of risk.
It is good to know Eskom has such a dedicated team of engineers whose years of experience is being pooled into the most important profit of any enterprise – the preservation of human life and betterment of safety.