25 th International Conference on Electricity Distribution Madrid, 3-6 June 2019 Paper n° 1096 CIRED 2019 1/5 ACTIVE AND PASSIVE SHIELD FOR AERIAL POWER LINES Aldo CANOVA Luca GIACCONE Vincenzo CIRIMELE Politecnico di Torino – Italy Politecnico di Torino – Italy Politecnico di Torino – Italy aldo.canova@polito.it luca.giaccone@polito.it vincenzo.cirimele@polito.it ABSTRACT The work presents a procedure to optimise a mixed passive and active shielding. The shielding concerns a building in proximity of a high voltage overhead line. This condition often arises in the reality. For Italian legislation, if the building is located at a distance that does not guarantee the respect of the limits on the magnetic flux density, the use of such building is not authorised for stays longer than 4 hours per day. In the case of overhead lines, the line operator can install a shielding acting directly on the source at the cost of difficult and expensive modifications to the pylons. The most feasible solution is to perform a shielding of the building which is generally passive and very rarely active. The selection of one or the other type of shielding is generally linked to factors external to the purely technical ones. This paper presents an optimised design of a shielding based on the use of both technologies. The search of the optimal condition has been based on performance parameters not considering cost constraints. The work presents two study cases characterized by different distances of the building that has to be protected from the power line. INTRODUCTION The current legislation on protection from exposure to electromagnetic field (EMF) inside and outside the European Community is not homogeneous. In the EU the Council of the European Union published in 1999 a Recommendation (1999/519/EC, commonly known in the field jargon as “the Recommendation”) on the limitation of exposure of general public to EMF (from 0 Hz to 300 GHz). The Recommendation contains the reference levels for the strength of EMF at the various frequencies [1]. The limits in both the Recommendation and the related Directive are derived from the 1998 Guidelines for limiting exposure to time-varying EMF by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [2]. ICNIRP has published new guidelines for EMF at frequencies between 1 Hz and 100 kHz in 2010, but these have not yet led to changes in EU legislation [3]. Since the Recommendation is not legally binding, the EMF policy can vary among member states. However, it is possible to individuate three different groups of countries adopting similar approaches [4]. In the first group of member states, the Recommendation has been transposed in binding national legislations. This means that the basic restrictions and the reference levels provided by the ICNIRP Guidelines must be directly adopted as national reference limits. The member states of this group are Czech Republic, Estonia, Greece, Hungary, Luxembourg, Portugal and Romania. In the particular case of Germany and Slovakia, the reference levels of the Recommendation are applied without any reference to the basic restrictions. In the second group of member states, the national limits based on the European Recommendation or ICNIRP Guidelines are not binding and the limits are less stringent or there is a lack of precise regulations. Member states in this group are Austria, Cyprus, Denmark, Finland, Ireland, Latvia, Malta, Netherlands and United Kingdom. Only in some of these countries a precautionary policy has been adopted and it has been suggested to electricity companies which can voluntarily conform. In the third group of member states, there are restrictions stricter than the ones directly provided by the Recommendation on the base of the precautionary principle that aims to protect people from possible long- term effects. Among these countries one can find: Belgium, France, Italy, Netherlands, Poland, Slovenia, Serbia, Sweden and Switzerland. In the present paper, the attention is mainly devoted to Italy where the basic limits for magnetic flux density are identical to the reference levels in the Recommendation but an attention value of 10 μT is applied to the exposure for periods longer than 4 hours in homes, hospitals, playgrounds and schools built before 2003 and a quality goal of 3 μT is applied to the same category of constructions built after 2003. The same restrictions are imposed also for the construction of new power lines, primary or secondary substations close to residential areas. In countries, like Italy, where magnetic induction limits are particularly low, it often happens that buildings located near to electrical sources require the installation of mitigation systems such as passive or active shields in order to be compliant with the legislative limits. The solution to this problem can present many difficulties. The presence of openings such as doors and windows has to be taken into account and it may compromise the effectiveness of the shielding. Furthermore, the installation of the shielding solution is more complicated if it has not been carried out during the construction of the building and a retrofit operation is required. Another kind of problems, the one mainly addressed in the present work, occurs when the distance of the building from the power line is at the same order of magnitude of the distance between the different phase conductors. In these cases, the shielding effectiveness, in particular when considering conductive passive shiels, may be compromised. The present work focuses on this issue presenting a