The accuracy of voltage and current measurements in Transmission and Distribution networks is particularly important for an ever-increasing number of applications no longer linked only to traditional functions, aimed at ensuring the correct configuration of the network in steady-state conditions (measurement applications) or transient conditions (protection), but to new needs and aspects, such as commercial and fiscal aspects linked to the liberalization of the electricity market, the quality of supply and phasor measurements.

Voltage transformers (VTs) and current transformers (CTs), used to adapt the voltage and current signals present in high voltage networks to the inputs of the measuring instruments used (meters, power meters, PMUs, etc.) without compromising their integrity, play an increasingly crucial role in the measurement chain, taking into account their transduction characteristics, which are potentially affected—depending on the technology used—by non-linearity, hysteresis and saturation, and subject to the influence of, among other things, temperature, proximity, aging, which are compatible with historical needs but no longer adequate for current needs.

The activities covered in this report were aimed in particular at:
• the executive design and start of construction of a prototype of an advanced three-phase Stand-Alone Merging Unit (S-SAMU3), for the characterization and on-site compensation of the behavior of the measurement transformers;
• updating the research and regulatory framework.

The activities carried out obtained the following products:
• the executive project of the S-SAMU3 prototype, developed starting from the experiences conducted in the previous reference periods, with the complications deriving from the management and synchronization of large data flows;
• the prototype of the electronic board relating to a single acquisition channel of the S-SAMU3.

Starting from the results obtained, we intend to complete the construction of the three-phase prototype of S-SAMU3 and then move on to the implementation phase of the measurement transformer models and verify the compensation methods for the non-linearities and errors introduced by these models.