It’s a very exciting time at National Grid – we have made two final decisions on the shape of the T-pylon family.
We were greatly impressed with the number of people who kindly took the time to tell us what they thought of the various design options we were weighing up. So we wanted readers of this blog to find out first that the T-pylon’s crossarm and monopole will have a circular cross section (or shape) and the tension pylon (used to turn corners in transmission lines) will be the Flying T. Also, the survey confirmed for us that most people prefer the T-pylon design over the traditional lattice structure.
First of all, on the shape side, we have opted for a circular design for the practical reason that making an elliptical shape that is tapered is a highly skilled activity and requires bespoke, expensive equipment. This would have greatly reduced the number of manufacturers we would have been able to work with. We obviously want to have a competitive bidding process when we come to pick a manufacturing partner in the future when we seek to develop these structures as part of a line delivering new low carbon generation connections. The simpler the design, the less complex the process will be and so the number of bidding companies will be higher and, hence, the possibility of lower fabrication costs will increase.
We had considered the elliptical design at great length and we know many people liked it as it introduced more innovation to the pylon. We realised that from a distance you would struggle to distinguish between the two shapes but when close-up and viewing the elliptical shape along its length, you would recognise the reduced dimension. The responses received indicated that a number of parties did not know or have a preference on either shape. So, the practical considerations of simplifying the design to reduce the manufacturing cost and potential construction issues won the day.
The public survey results from readers of this blog were very close with the Triple T (with three crossarms), just ahead of the Flying T (single cross arm) and with the Double T trailing (two crossarms) in third place.
We completely understand why the Triple T was marginally favoured and we’re glad that it was so close to the Flying T because, as mentioned, it’s the Flying T we’re going with. The public gave their view on the options before them based on aesthetics and, of course, that is important. However, there are other issues, mainly around sustainability, constructability and cost which have led us to select the Flying T. The most striking point, of course, is when you see the Flying T next to its suspension pylon sister, you see a natural fit; they resemble one another and so form a natural ‘family’.
The Triple T was one of the early design options that Bystrup showed during the international pylon competition held in 2011. The judges’ view at the time was that the Triple T significantly deviated from the T-pylon family with its multitude of crossarms and notable different shape. Seen in the context of a line on the landscape, the Triple and Double Ts would attract unnecessary attention and counteract our main intention of reducing visual impact.
The Flying T therefore emphasises the T-shape and enables the wires on a line of pylons to flow at the same height, as opposed to the lattice pylons where the suspension and tension pylon wires rise and fall with the different pylon designs. It also has the ability to be further optimised to lighten the appearance of the design and also the structural weight. The Flying T will help us to minimise the visual impact of the transmission line on the landscape.
T-pylon to lattice
The survey also gave us a chance to ask the public to compare the new T-pylon with the traditional lattice design. The majority of respondents felt the T-pylon offered a modern twist to existing pylon designs as its simple design and short height offer a sleek shape, meaning it could potentially blend better into varied landscapes. People also identified the smaller footprint of the T-pylon as a benefit when associated with the impact on farming and future land re-sale values.
There was also recognition though that the iconic lattice structure, with its semi-transparent design, had its place in some very open landscape and, by virtue of its longevity in operation, was familiar to people.
Sustainability and cost
Like any responsible organisation, sustainability is a major issue for National Grid and so a huge downside of progressing a design with two or three crossarms, instead of one, would have been the very obvious point of more material and energy being required to produce the structure.
We expect that the single crossarm design of the Flying T can be further optimised to save weight, compared to the Triple T. This means there is not only a saving in manufacturing cost but there is also the benefit of having fewer, lighter parts to drive to the construction site and fit together.
When you consider that as many as every one in ten pylons in a transmission line on some routes could be tension pylons, you start to get an idea of how much of a saving in materials, transportation cost, fuel and construction time this could amount to.
The savings will greatly boost the sustainability of new transmission lines. Less steel and fewer truck trips to deliver components will significantly lower carbon emissions and use of finite resources.
So, the T-pylon design will be circular and the Flying T design will be the tension pylon we’ll take forward. Both decisions will move us forwards with practicality and cost as our central considerations which, of course, go hand in hand with our commitment to sustainability.
View of the pylons
Triple T in the T-pylon Family
Double T in the T-pylon Family
Flying T in the T-pylon Family