The “Electrify” Loop Pylon is the result of an aesthetic and technical design optimization strategy. The optimization parameters are:

Visual impact – by allowing the structure to rotate around it’s ground pivot point, view corridors can be preserved as well as visual impacts on landmarks and natural heritage can be minimized.

Formal language – the elliptical loop shape form reflects harmonic natural objects such as leaves, bubbles and hills. The soft white silhouette blends seamlessly and without sharp corners from the bottom to the top into natural backgrounds and the sky. Ground impact is minimized by attaching the loop on a single point foundation making it visually less heavy and permanent than conventional pylons.

Global flexibility – all loop pylons can be constructed and mounted in various degrees of rotations against the linear power line direction. Within the current proposal orientations of 0.0°, 17.5° and 35.0°(maximum to compensate the 110° site condition) are foreseen. Additional orientations are possible within the system allowing for a wide range of global effects in the visual appearance of the power line.

Family variations – Within the proposed loop design a range of family members is already anticipated. Various combinations of 330KV & 110KV phases, as well as medium and low voltage pylons can be constructed for an overall unified look.

Height & Weight – the loop design allows a reduction of the tower height down to 32.5 m including the lightning protection wires. With a deadweight of 14.4 tons the 35.0° rotated corner pylon is very light while achieving all structural requirements.

Structural Description

General – The design for the new Harku-Lihula-Sindi high voltage line is based on a family of elliptical pylons with a default height of 32.5 meters. Pylons can be oriented either 0.0°, 17.5° or 35.0° according to the perpendicular power line axis and have a deadweight of 12.8, 13.7 and 14.4 tons. Additional orientations can be realized on request within the design system. Power line phases are clustered within a triangular grid that provides efficiency regarding the overall outline and height.

Pylon Structure – The elliptical pylon’s steel cross-sections vary from a corner rounded rectangular tube of 200x500mm at the top up to 700x1200mm at the bottom point with wall thickness between 3mm and 12mm adjusted according to the governing bending moments. Cross-sections are designed for a slender silhouette fostering the elegant, unobtrusive design and reduced wall thickness, allowing for an efficient manufacturing from rolled sheet metal. Large cross sections are stiffened by interior ribs preventing local buckling. At the lowest point of the elliptical ring the structure is supported by steel plates which are bolted onto the foundation socket. Locating the power line phases in the middle of the structure significantly reduces bending and torsion moments of the governing design load-case (wind + three asymmetric broken cables) and thus reduces steel weight and costs.

Cable Support Structure – The cable support structure consists of a triangular grid of insulated truss members inside the upper area of the elliptical structure. The grid offers sufficient space to mount three 110kV phases as well as three 330kV phases and can optionally be extended to support nine phases. Horizontal members are designed to allow access to interior cables by climbing.

Assembly & Transportation – The Pylon structure is assembled from 5 elliptical ring segments with maximum dimensions of 4x8meters up to 2x16meters allowing for easy transportation – the maximum weight of one segment is less than 3.5to. The connection of the individual segments is designed as a bolted flange connection positioned at the interior of the steel tube. Assembly openings allow access to these connection details.

Corrosion Protection – Steel elements are conceived to be corrosion protected either by a painted coating or galvanization.

Foundation – The pylon structure is supported by a socket on top of an underground slab foundation which is reducing the footprint and land usage. Depending on the ground conditions, the underground slab can be reduced and combined optionally with four bored piles or eight micropiles which can be set by lightweight machinery.

Maintenance – The pylon structure can be maintained without a lift cart by climbing on handholds from four meters height on. The interior of the supporting grid is also accessible for maintenance via climbing on its horizontal members.

Project Team:
Moritz Heimrath
Quirin Krumbholz

Structural Consultant: