On-site live installation of Hv equipment for insrument accuracy check.

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 one here presented: the live working installation of a reference measuring system for on-site accuracy check of 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 transmission 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, while the Rogowski coil can be positioned with a bare-hand technique. The innovative methodology was set up and successfully experimented 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 to installed measurement apparatus features, allowing to avoid service interruption during insertion operations. 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). 1 Foreword HV instrument transformers accuracy may deteriorate with ageing, as demonstrated by recent studies and laboratory tests [1]. The reduction of the instrument transformers accuracy causes slight unbalances in power measurement, which may translate into heavy unbalances in energy measurement and, consequently, in money flows associated with metering and energy trading. Moreover, for transparency and correctness reasons, to all electricity market actors should be granted the right of being able to check, at scheduled time intervals or whenever desired, that HV components of energy measurement chains be accurate, exactly as happens for the LV ones (meters). In the past this was possible only theoretically, since service removal was necessary for current transformers and often for voltage transformers too, adding to the costs