Instrument transformers are needed in order to perform voltage, current and energy measurement in High Voltage and their accuracy is more and more crucial not only for the electricity market but also for new applications, such as, for example, synchrophasors. New methodologies and equipment have been set up in Italy in order to verify their accuracy and possibly, in the future, to calibrate them on site. Live line working distance methods allow a fast, non-intrusive installation procedure of the Reference Measuring Systems (RMS), without need for de-energization of the relevant busbars. The Current RMS can be installed in few minutes; a new kind of disconnector switch, has been purposely conceived and developed in order to connect the voltage RMS, a RC divider, to the HV network: the Simplified Transportable Disconnector (STD) is easily transportable and can be deployed and connected within twenty minutes to HV networks having rated voltage up to 400 kV. The whole methodology and equipment have been successfully tested on-site: their availability is very important for the future developments in the field of HV current and voltage measurements, taking into account both the evolution of instrument transformers towards the digital communication world and their new possible uses in the framework of the smart grid.