In many countries, construction of new HV and EHV overhead lines has triggered divisive public debate, with particular resistance against the use of traditional lattice towers. In the face of this, one way to promote greater acceptance and also minimize the impact of new lines is by using alternatives such as compact and ‘designer’ structures. This edited contribution by Alexander Braun of Europoles in Germany, offered an overview on the status of alternative pole designs with a focus on achieving the right balance between the competing demands of design, operational safety, public acceptance and cost-effectiveness.
Grid Expansion & Politics
The shift in energy generation from traditional large-scale power plants toward smaller renewable energy producers combined with geographic changes in production hubs and new cross-border interconnections have required comprehensive restructuring of power grids, especially in the HV and EHV segments. Grid operators these days not only have to meet statutory requirements (including security of supply, non-discriminatory access as well as economic set-up and operation); they also have to ensure that the people most affected recognize the necessity for and accept new line routes. That is why planning and construction of overhead lines today has become a process largely defined by politics and often involves decision-making at the highest levels of government.
Public opposition plays a key role, given reservations about the construction of new power lines and the possible effects on the environment and on people (i.e. electromagnetic field, impact on tourism and changes to the landscape). Apart from an effective communication strategy, early involvement of those affected and an open approach to objections and concerns, there are also various technical options that can help promote acceptance of new power infrastructure. One option is to use technologies such as full underground cabling, DC transmission (in combination with buried cable) or low-sag cable. However, these alternatives are constrained by technical risks since they have not yet been proven over long-term service experience. In addition, the high costs involved in extensive groundwork present a serious drawback when it comes to buried cable.
An important element of grid expansion is maximizing use of existing corridors and, where possible, upgrading existing power lines. Grid expansions enjoy the highest acceptance levels in these areas and approvals are generally issued sooner. In order to encourage greater acceptance, better utilize existing corridors and minimize impact of new lines, alternative designs such as compact lines have been used for decades. More recently, international architectural competitions (e.g. as held by Terna in Italy, National Grid in the UK, RTE in France, etc.) have also highlighted new, more acceptable pole designs.
Achieving Balance Between Design, Public Acceptance, Technical Safety & Cost
In practical terms, any new pole structures have to meet all the various requirements imposed, particularly by grid operators themselves. In this context, design can sometimes play a subordinate role. What is equally and often more important are technical safety, cost-effectiveness and operating costs (including maintenance costs). The challenge then is to meet all these requirements while at the same time utilizing an aesthetically pleasing design, i.e. one that guarantees safe operation of lines that are also economical to build and run.
This process has to take account of a lot of different variables and stakeholder interests, a selection of which are listed below:
• Lower height;
• Modern infrastructure;
• Possibility to ‘have a choice’;
• Narrower right-of-way;
• Reduced EM fields;
• Reduced impact on landscape;
• Participation in decision-making;
• Pleasing design.
• National standards;
• Structural stability requirements;
• Ageing & fatigue;
• Corrosion protection;
• Lifetime >80 years;
• Earthing & lightning protection;
• Induced currents;
• Electrical clearance;
• Electrical requirements;
• Electromagnetic fields.
• Test programs;
• Development costs;
• External consultants;
• Training costs;
• Costs for extra design;
• Pole costs;
• Foundation costs;
• Marketing costs.
In general, the public is against construction of new power lines, especially overhead lines. Therefore, to mitigate the impact, poles have now been developed (e.g. in the Netherlands, Italy, France and Switzerland) that allow lower height, smaller footprint and narrower corridor. In addition, architectural competitions have been held to encourage new shapes of pole and to further limit magnetic field by arranging overhead conductors in a circle that is as narrow as possible.
Basically, while these innovations may offer significant advantages over conventional lattice structures, they still have to meet the same standards for safety and cost effectiveness.
A research program was conducted by Europoles, Fichtner and Lapp Insulators in collaboration with the Technical Universities of Brunswick and Dresden and the Karlsruhe Institute for Technology (KIT). As part of this project, also funded by the German Federal Ministry of Economic Affairs and Energy, new construction methods, materials and designs were tested in respect to their mechanical strength and applicability to the high voltage field. The goal was to find a structure that would meet all requirements for maintenance and operation and also avoid additional technical risks for the grid operator. For example, load tests were performed on concrete poles as well as composite insulators and electrical tests were undertaken to determine the effect on pole materials and insulators of electric field, leakage current and disruptive discharges.
Results of the testing demonstrated that, thanks to modern calculation methods as well as experience and know-how in fabricating insulators and poles, modern materials and designs do indeed meet all the technical requirements for the safe operation of HV and EHV transmission lines.
Based on the results of the research, pole designs could be optimized by identifying cost drivers, structural improvements, use of insulated cross-arms, modern materials and development of innovative foundation methods that are competitive with conventional latticework structures.
Modern pole designs can indeed help grid operators obtain greater acceptance for new overhead lines and/or also reduce their known negative effects. Use of modern materials, calculation methods and tests also has made it possible to ensure that all requirements for technical safety and cost efficiency are met as well.