During the 3 years of regional consultations, the NNA document was gradually updated and improved in its quality. The PTB project supported the regional working group since late 2018, mainly by consultancy through international experts with hands-on experience from EU countries that have accomplished their NNA. The present version of the draft NNA consists of 173 pages. Comparative calculations based on the old and new standard (with NNAs) need to be carried out as one of the next steps, to ensure a practicable use of the new design method.
After finalisation of the draft, the document will enter the stage of a public consultation process in the concerned countries. After this the NNA will be forwarded to CENELEC for approval as official CENELEC NNA to EN 50341-1 of the respective countries.
The main challenges / innovations required by the use of EN50341 and the NNA compared to the previous and still valid technical regulation from the Yugoslav era are the following:
- The change from the deterministic design practice (based on a long tradition of empirical design methods) to the new probabilistic design (based on probabilities, return periods and reliability levels)
- The change to Eurocodes, which are nowadays state of the art for the dimensioning of structures
- The introduction of a structural design method in EN 50341 which is based on the limit state concept used in conjunction with the partial factor method
- The non-availability of sufficient climatic data in broad areas of the concerned countries
- The coordination of the new approach between all parts of an overhead line, from earthing grid, foundation, structure, conductors, insulators, fittings and ground wires as well as electrical clearances to ground and any kind of objects in the vicinity of a line.
All CENELEC countries have to establish their NNAs to complement the “main body” of EN50341. The group benefited from the experience from the establishment of NNAs in Austria, Germany and Slovenia. This helped much to reduce time, efforts and expenses for the establishment of the said NNAs.
More information on this project can be found in the SEE QI 3 final report under https://see.ptb.de/see-qi-projects/standardization-overhead-electrical-lines/