The accuracy of voltage and current measurements in Transmission and Distribution networks is increasingly important for a growing number of applications. These are no longer limited to traditional functions aimed at ensuring the correct network setup under steady-state conditions (measurement applications) or during transients (protection), but also include new requirements and aspects such as commercial and fiscal concerns related to the liberalization of the electricity market, supply quality, and phasor measurements. Voltage transformers (VT) and current transformers (CT), used to adapt the voltage and current signals in High Voltage networks to the inputs of the measuring instruments (meters, power meters, PMUs etc.) without compromising their integrity, play an increasingly crucial role in the measurement chain. Their transduction characteristics, which may be affected, depending on the technology used, by non-linearity, hysteresis, and saturation, and influenced by factors such as temperature, proximity, and aging, are certainly compatible with historical needs but are no longer adequate for current requirements.

The availability and expected widespread adoption of equipment designed to digitize the analog voltage and current signals from measurement transformers installed in the Transmission and Distribution networks, known as Stand-Alone Merging Units (SAMU), suggest the possibility of enriching their standardized functionalities with more advanced tools aimed at compensating for the errors and non-linear, hysteretic, and saturation behavior of the measurement transformers themselves. Last but not least, SAMUs could also ensure certain functionalities usually performed by measuring devices such as power meters and phasor measurement units.

The activities conducted and reported in this document concern the completion of the SSAMU³ prototype with advanced functionalities, both in terms of hardware and software, and the definition of the tests that will be conducted to characterize it. The S-SAMU³ will be used for accurate measurement of harmonic content and Power Quality events, as well as for compensating for the non-linearities introduced by VTs and CTs through the use of compensation models developed in collaboration with Italian universities working on these topics.