Thanks to its physical and chemical properties, which make it an excellent insulator, SF6 (sulfur hexachloride) is used as an insulator in some kinds of electrical equipment, thus allowing more compact versions of the latter to be produced. Equipment insulated with SF6 is more reliable, as well as less bulky. Because of these properties, it is foreseen that equipment with SF6 will be increasingly used, as it is transmission companies abroad.
Part of the gas present in infrastructure is dispersed in the air because of the defective tightness of gaskets and sometimes also during pressure restoration. SF6 is classified as a greenhouse gas. Ternai therefore intends to keep SF6 leakage under control to contain and, if possible, reduce its incidence with respect to the total
quantity of the gas used. (In absolute terms, however, the quantity of dispersed gas could be larger, because of the increased use of equipment insulated with SF6.)

According to the plans for installing new equipment, the foreseeable reduction of the incidence of leakage is 0.1% in five years from when the start of the installation campaign. The latter began in 2009, but is conditioned by the actual availability of equipment with less leakage developed by suppliers. In 2010 Terna began an internal study to identify equipment with anomalous leakage and assess the feasibility of a program of targeted maintenance. The study results will enable the Company to establish a more precise target value for the incidence of SF6 leakage.
Program/initiative 2009 2010
New procedure for monitoring leakage(1) and reduction of dispersion during pressure restoration. Application of procedure to all plants for the entire year.  
Integrated compact modules (set of different kinds of equipment) with a reduction of at least 30% of the SF6 necessary for insulation with respect to steel-clad uprights. After the positive trial results, the equipment is considered an applicative standard and will be installed as necessary. Installation of the first modules to test their actual performance.
Detection systems with remote transmission of leakage of the gas in equipment (2) Installation on the 380-kVi section of the Lacchiarella electric station completed. Assessment of results and widespread application.
New highly reliable TA measurement transformers sealed or with maximum leakage of 0.1% a year (3) Type trials concluded and production started Plan for replacing old equipment with new, highly reliable equipment with very low leakage.

(1) The new detection system includes recording of the gas used and dispersed for each station; until 2007, measurement of leakage was based on the total quantity of SF6 purchased, net of new installations.

(2) The early detection by the remote-maintenance center of the equipment where the pressure of the gas is falling anomalously allows the Company to do targeted work on the equipment, thus also avoiding plant downtime because of insulator leakage.
(3) The particularity of this initiative, which was motivated by the detection of leakage exceeding the declared thresholds, resides in the current lack on the market of equipment ensuring a very low leakage level over time.