Check Giorgio De Donà**, Paolo Mazza*, Nikola Kuljaca*, Gabriella Crotti***, Angelo Sardi***, Stephan Weiss****, Uwe Brand*****, Michel Giraud***** ICOLIM 2006, Praga 7-9 Giugno 2006 *CESI RICERCA **TERNA S.p.A. ***I.N.RI.M ****Interoptix U.S.A. *****Schniewindt Germany Live working is not useful for line or substation maintenance activities only, although this is the more common application: other practices are made possible too, such as measurement devices installation. Besides well known donuts for line temperature measurement, other new, important applications are currently being developed, such as the present one: the live working installation of a reference measurement system for on-site accuracy check of in-service instrument transformers. The reference system is composed by live-installable transducers for voltage and current (a capacitive-resistive voltage divider and a split-core, openable Rogowski coil), optical data trans-mission and a data acquisition and analysis system. The reference voltage divider can be installed using a hand operated “distance” technique, by means of a copper plait inserted in a reel connected to a short-circuit device, the Rogowski coil with a bare-hand technique. The innovative methodology was set up and successfully applied in Italian Rondissone HV substation in the frame of a research project led by CESI S.p.A. Innovation is not related to intervention typology, common to a lot of live working activities, but to coupling between such techniques and a measurement apparatus having such a low measurement uncertainty, allowing to avoid service interruption. This work has been supported by MAP (Italian Ministry for Productive Activities) in the frame of Public Interest Energy Research Project named "Ricerca di Sistema" (MAP Decree of February 28th, 2003).