SITE live verification of HV intrument transformers Nikola Kuljaca*, Paolo Mazza*, Gabriella Crotti**, Angelo Sardi**, Giorgio De Donà*** Congrès International de Métrologie 2007 Lille (France), 18-21 Giugno 2007 * CESI RICERCA ** IN.RI.M *** TERNA SpA Prototype reference measuring systems (RMS) for the on-site verification of high voltage instrument transformers for energy metering have been set up. Their use can make possible the identification, without service removal, of the current and voltage transformers which no longer comply with the accuracy requirements. Specific measurement procedures have been experimented in the characterisation of the RMSs, which include as reference transducers a Rogowski coil and a resistive-capacitive divider for the current and voltage measurement respectively. The uncertainty associated with the on-site use of the RMSs is evaluated considering the operating conditions which are likely to occur. The results obtained in the first tests carried out show the feasibility of a live, on-site accuracy check of the instrument transformers.